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Archive for May, 2011

New research from last week 21/2011

Posted by Ari Jokimäki on May 30, 2011

Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as they are published. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. Here’s the archive for the news of previous weeks. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news. Planet 3.0 also reports new research.

Published last week:

Deglacial CO2 rise might not be from the oceans

Deglacial radiocarbon history of tropical Atlantic thermocline waters: absence of CO2 reservoir purging signal – Cléroux et al. (2011) “A current scenario to explain much of the atmospheric CO2 increase during the Glacial to Holocene climate transition requires the outgassing of a deep, old oceanic CO2 reservoir thought to be located in the Southern Ocean. In this scenario, CO2-rich and 14C-depleted subsurface Antarctic-sourced water, ventilates the thermocline where it is purged to the atmosphere in the equatorial regions, a view that has been met with conflicting results. Using a novel approach (paired surface and deep-dwelling planktonic foraminifer radiocarbon analyses), we document that the equatorial Atlantic thermocline did not see old, 14C-depleted water, which would be characteristic of the proposed isolated deep ocean CO2 reservoir. Data from several studies concur that, during the deglaciation, Antarctic intermediate waters were contributing to Atlantic thermocline waters even more than today, therefore, our observations challenge the current purging hypothesis. Together with other studies, these results suggest that the mechanism responsible for the deglacial CO2 rise cannot invoke contemporary circulation modes and/or thermocline ventilation pathways.” Caroline Cléroux, Peter deMenocal and Thomas Guilderson, Quaternary Science Reviews, doi:10.1016/j.quascirev.2011.04.015.

New aerosol-cloud effect has significance to climate

The aerosol–Bénard cell effect on marine stratocumulus clouds and its contribution to glacial-interglacial cycles – Bar-Or et al. (2011) “Aerosol-cloud interactions, such as aerosol loading in convective clouds resulting in either precipitation suppression or cloud invigoration, in higher cloud tops, and in longer-lived clouds, are well known. Here we investigate a new aerosol-cloud interaction, the effect of aerosol loading on Bénard cells, on the stratocumulus cloud fraction, and ultimately on the climate over glacial-interglacial cycles, using a two-dimensional model running a million year continuous simulation. This radiative effect is observed only in marine boundary layer stratocumulus clouds that have a convective cellular structure. Recent research suggests that aerosols can switch the direction of convection in Bénard cells (from open cells to closed cells) by suppressing precipitation and therefore dramatically change the cloud fraction. The effect investigated in this work differs from previously known aerosol effects on convective clouds by its intensity and magnitude and has never been taken into account in past climate simulations. The results show that accounting for the aerosol–Bénard cell effect alone contributes a negative radiative forcing, affecting both the Northern Hemisphere mean annual surface temperature and ice volume. Adding the aerosol–Bénard cell effect to the direct radiative effect of dust and to the effect of dust on snow and ice albedo shows that the aerosol–Bénard cell effect plays a significant role in glacial-interglacial climate change, strengthening the earlier glacial cycles and creating a larger glacial-interglacial surface temperature amplitude while preserving the continental ice volume amplitude. Because of the model limitations, there are a number of uncertainties involved. However, the results serve to give a preliminary evaluation of the aerosol–Bénard cell effect at least qualitatively if not quantitatively.” Bar-Or, R. Z., H. Gildor, and C. Erlick (2011), J. Geophys. Res., 116, D10119, doi:10.1029/2010JD014470.

Are coasts uplifting worldwide?

Relative sea-level fall since the last interglacial stage: Are coasts uplifting worldwide? – Pedoja et al. (2011) “The growing interest in quantification of vertical ground motion stems from the need to understand in detail how the Earth’s crust behaves, for both scientific and social reasons. However, only recently has the refinement of dating techniques made possible the use of paleoshorelines as reliable tools for tectonic studies. Although there are many local studies of Quaternary vertical motions of coastlines, we know of no comprehensive worldwide synthesis. Here we provide a compilation of 890 records of paleoshoreline sequences, with particular emphasis on the last interglacial stage (Marine Isotopic Stage [MIS] 5e, ~ 122 ka). The quality of dating MIS 5e makes it a reliable marker to evaluate vertical ground motion rates during the late Quaternary on a global scale. The results show that most coastal segments have risen relative to sea-level with a mean uplift rate higher than 0.2 mm/yr, i.e. more than four times faster than the estimated eustatic drop in sea level. The results also reveal that the uplift rate is faster on average for active margins than for passive margins. Neither dynamic topography nor glacio-hydro-isostasy may explain sustained uplift of all continental margins, as revealed by the wide distribution of uplifted sequences of paleoshorelines. Instead, we suggest that only plate-tectonic processes reconcile all observations of Quaternary coastal uplift. We propose that long-term continental accretion has led to compression of continental plates and uplift of their margins. Therefore this study concludes that plate-tectonics processes impact all margins and emphasizes the fact that the notion of a stable platform is unrealistic. These results therefore seriously challenge the evaluation of past sea levels from the fossil shoreline record.” Kevin Pedoja, Laurent Husson, Vincent Regard, Peter Robert Cobbold, Emilie Ostanciaux, Markes E. Johnson, Stephen Kershaw, Marianne Saillard, Joseph Martinod, Lucille Furgerot, Pierre Weill and Bernard Delcaillau, Earth-Science Reviews, doi:10.1016/j.earscirev.2011.05.002.

Temperature annual cycle amplitude trends in China

Nonlinear trend in the amplitude of the temperature annual cycle in China and its implication for climate change research – Qian et al. (2011) “Climate change is not only reflected by the changes in annual means of climate variables, but also by the changes in their annual cycles (seasonality), especially in the regions outside the tropics. In this study, the ensemble empirical mode decomposition (EEMD) method is applied to investigate nonlinear trend in the amplitude of the annual cycle (which contributes 96% of total variance) of China’s daily mean surface air temperature for the period 1961–2007. The results show that variation and change in the amplitude are significant, with a peak-to-peak annual amplitude variation of 13% (1.8°C) of its mean amplitude and a significant linear decrease in amplitude by 4.6% (0.63°C) for this period. Also identified is a multidecadal change in amplitude from significant decreasing (−1.7%/decade or −0.23 °C/decade) to significant increasing (2.2%/decade or 0.29°C/decade) occurring around 1993 that overlaps the systematic linear trend. This multidecadal change can be attributed mainly to the change in surface solar radiation, from dimming to brightening, rather than to warming or an enhanced greenhouse effect. We further propose that the combined effect of the global dimming/brightening transition and a gradual increase in greenhouse warming has led to a perceived warming trend that is much larger in winter than in summer and to a perceived accelerated warming in the annual mean since the early 1990s in China. We also note that the deseasonalization method (considering either the conventional repetitive climatological annual cycle or the time-varying annual cycle) can also affect trend estimation.” Cheng Qian, Congbin Fu, Zhaohua Wu, Journal of Climate 2011, doi: 10.1175/JCLI-D-11-00006.1.

Lessons from early Holocene sea level rise

The early Holocene sea level rise – Smith et al. (2011) “The causes, anatomy and consequences of the early Holocene sea level rise (EHSLR) are reviewed. The rise, of ca 60m, took place over most of the Earth as the volume of the oceans increased during deglaciation and is dated at 11,650–7000 cal. BP. The EHSLR was largely driven by meltwater release from decaying ice masses and the break up of coastal ice streams. The patterns of ice sheet decay and the evidence for meltwater pulses are reviewed, and it is argued that the EHSLR was a factor in the ca 8470 BP flood from Lake Agassiz-Ojibway. Patterns of relative sea level changes are examined and it is argued that in addition to regional variations, temporal changes are indicated. The impact of the EHSLR on climate is reviewed and it is maintained that the event was a factor in the 8200 BP cooling event, as well as in changes in ocean current patterns and their resultant effects. The EHSLR may also have enhanced volcanic activity, but no clear evidence of a causal link with submarine sliding on continental slopes and shelves can yet be demonstrated. The rise probably influenced rates and patterns of human migrations and cultural changes. It is concluded that the EHSLR was a major event of global significance, knowledge of which is relevant to an understanding of the impacts of global climate change in the future.” D.E. Smith, S. Harrison, C.R. Firth and J.T. Jordan, Quaternary Science Reviews, doi:10.1016/j.quascirev.2011.04.019.

More evidence for tropical belt widening

Poleward Shift of Subtropical Jets Inferred from Satellite-observed Lower Stratospheric Temperatures – Fu & Lin (2011) “One pronounced feature in observed latitudinal dependence of lower-stratospheric temperature trends is the enhanced cooling near 30° latitudes in both hemispheres (Fu et al. 2006). The observed phenomenon has not, to date, been explained in the literature. This study shows that the enhanced cooling is a direct response of the lower-stratospheric temperature to the poleward shift of subtropical jets. Further, this enhanced lower-stratospheric cooling can be used to quantify the poleward shift of subtropical jets. Using the lower-stratospheric temperatures observed by satellite-borne microwave sounding units, it is shown that the subtropical jets have shifted poleward by 0.6 ± 0.1 and 1.0 ± 0.3 degrees latitude in the southern and northern hemispheres, respectively, in last 30 years since 1979, indicating a widening of tropical belt by 1.6 ± 0.4 degrees latitude.” Qiang Fu and Pu Lin, Journal of Climate 2011, doi: 10.1175/JCLI-D-11-00027.1.

Climate information from sediment sand grain size

Patterns of local and regional grain size distribution and their application to Holocene climate reconstruction in semi-arid Inner Mongolia, China – Yin et al. (2011) “The semi-arid temperate steppe in northern central China is one of the main areas influenced by frequent dust and sand storms, and is at the same time a primary source of dust from deteriorated grasslands; thus, the sediment grain size distribution of inland lakes in this region can be a particularly useful indicator of palaeoenvrionmental change. The local pattern of grain size suggests that aeolian activity is the most important agent for sedimentation in the lake center in this region, as strong northwesterly winds prevail for most of the year and the surface runoff is very weak. Meanwhile, the regional pattern of topsoil grain size and its close association with mean annual precipitation (MAP) allows the establishment of a statistical model for palaeo-moisture reconstruction from sediment grain size. In this study, we reconstructed a humidity time series based on the sediment grain size sequence from Anguli Nuur Lake on the southern Inner Mongolian Plateau in China and found that it coincides very closely with the C/N ratio (carbon to nitrogen ratio) and other humidity indices revealed in previous studies of this temperate steppe region and from the δ18O values of stalagmite calcite in southern, monsoon-dominated China. This close relationship suggests that climate change in the semi-arid areas of Asia is strongly influenced by the Pacific summer monsoon and that it is reasonable to use sediment grain size as an indicator of humidity variability in the semi-arid steppe region. The reconstructed humidity increased during the early Holocene, and generally humid conditions lasted from about 10,400 until 7,000 yr BP. The period from around 7,000 to 5,200 yr BP was a transition phase from humid to semi-arid conditions, and the monsoon intensity of that time may have been at the threshold for a semi-arid vegetation ecosystem. Finally, since approximately 5,200 yr BP to present, the climate has become more arid, with corresponding vegetation deterioration and strong aeolian activity.” Yi Yin, Hongyan Liu, Siyuan He, Fengjun Zhao, Jiangling Zhu, Hongya Wang, Guo Liu and Xiuchen Wu, Palaeogeography, Palaeoclimatology, Palaeoecology, doi:10.1016/j.palaeo.2011.05.011.

Ice discharge from Greenland and Antarctic glaciers continues to increase

Accelerating ice loss from the fastest Greenland and Antarctic glaciers – Thomas et al. (2011) “Ice discharge from the fastest glaciers draining the Greenland and Antarctic ice sheets – Jakobshavn Isbrae (JI) and Pine Island Glacier (PIG)– continues to increase, and is now more than double that needed to balance snowfall in their catchment basins. Velocity increase probably resulted from decreased buttressing from thinning (and, for JI, breakup) of their floating ice tongues, and from reduced basal drag as grounding lines on both glaciers retreat. JI flows directly into the ocean as it becomes afloat, and here creep rates are proportional to the cube of bed depth. Rapid thinning of the PIG ice shelf increases the likelihood of its breakup, and subsequent rapid increase in discharge velocity. Results from a simple model indicate that JI velocities should almost double to >20 km a−1 by 2015, with velocities on PIG increasing to >10 km a−1 after breakup of its ice shelf. These high velocities would probably be sustained over many decades as the glaciers retreat within their long, very deep troughs. Resulting sea-level rise would average about 1.5 mm a−1.” Thomas, R., E. Frederick, J. Li, W. Krabill, S. Manizade, J. Paden, J. Sonntag, R. Swift, and J. Yungel (2011), Geophys. Res. Lett., 38, L10502, doi:10.1029/2011GL047304.

Global warming affects Earth’s rotation too

GRACE era secular trends in Earth rotation parameters: A global scale impact of the global warming process? – Roy & Peltier (2011) “Recent trends in the two primary anomalies in the rotational state of the planet are analyzed in detail, namely those associated with the speed and direction of polar wander and with the non-tidal acceleration of the rate of axial rotation (via the measurement of the changing oblateness of the Earth’s shape). It is demonstrated that a significant change in the secular trends in both of these independent parameters became evident subsequent to approximately 1992. It is suggested that both parameters might have come to be substantially influenced by mass loss from both the great polar ice sheets, and from the very large number of small ice-sheets and glaciers that are also being influenced by the global warming phenomenon. The modern values for the secular drifts in those parameters that we estimate are appropriate to the period during which measurements have been made by the satellites of the Gravity Recovery and Climate Experiment (GRACE). These changes in secular rates might greatly assist in understanding why the GRACE-inferred values of the time derivatives of the degree two and order one Stokes coefficients differ so significantly from those associated with Late Quaternary ice-age influence.” Roy, K., and W. R. Peltier (2011), Geophys. Res. Lett., 38, L10306, doi:10.1029/2011GL047282.

Snowline altitude changes in Andes mountains of Peru

Landsat TM and ETM+ derived snowline altitudes in the Cordillera Huayhuash and Cordillera Raura, Peru, 1986–2005 – McFadden et al. (2011) “The Cordilleras Huayhuash and Raura are remote glacierized ranges in the Andes Mountains of Peru. A robust assessment of modern glacier change is important for understanding how regional change affects Andean communities, and for placing paleo-glaciers in a context relative to modern glaciation and climate. Snowline altitudes (SLAs) derived from satellite imagery are used as a proxy for modern (1986–2005) local climate change in a key transition zone in the Andes. Clear sky, dry season Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper (ETM+) satellite images from 1986–2005 were used to identify snowline positions, and their altitude ranges were extracted from an Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) digital elevation model (DEM). Based on satellite records from 31 glaciers, average snowline altitudes (SLAs), an approximation for the equilibrium line altitude (ELA), for the Cordillera Huayhuash (13 glaciers) and Cordillera Raura (18 glaciers) from 1986–2005 were 5051 m a.s.l. from 1986–2005 and 5006 m a.s.l. from 1986–2002, respectively. During the same time period, the Cordillera Huayhuash SLA experienced no significant change while the Cordillera Raura SLA rose significantly from 4947 m a.s.l. to 5044 m a.s.l.” McFadden, E. M., Ramage, J., and Rodbell, D. T., The Cryosphere, 5, 419-430, doi:10.5194/tc-5-419-2011, 2011. [Full text]


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Papers on global warming and Earth’s rotation

Posted by Ari Jokimäki on May 25, 2011

This is a list of papers on global warming effects to Earth’s rotation. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

UPDATE (October 20, 2020): Zotov et al. (2016) and Mitrovica et al. (2015) added.

A possible interrelation between Earth rotation and climatic variability at decadal time-scale (Zotov et al. 2016) (OPEN ACCESS) “Using multichannel singular spectrum analysis (MSSA) we decomposed climatic time series into principal components, and compared them with Earth rotation parameters. The global warming trends were initially subtracted. Similar quasi 60 and 20 year periodic oscillations have been found in the global mean Earth temperature anomaly (HadCRUT4) and global mean sea level (GMSL). Similar cycles were also found in Earth rotation variation. Over the last 160 years multi-decadal change of Earth’s rotation velocity is correlated with the 60-year temperature anomaly, and Chandler wobble envelope reproduces the form of the 60-year oscillation noticed in GMSL. The quasi 20-year oscillation observed in GMSL is correlated with the Chandler wobble excitation. So, we assume that Earth’s rotation and climate indexes are connected. Despite of all the clues hinting this connection, no sound conclusion can be done as far as ocean circulation modelling is not able to correctly catch angular momentum of the oscillatory modes.” Leonid Zotov, C. Bizouard, C.K. Shum (2016). Geodesy and Geodynamics, Volume 7, Issue 3, Pages 216-222,

Reconciling past changes in Earth’s rotation with 20th century global sea-level rise: Resolving Munk’s enigma (Mitrovica et al. 2015) (OPEN ACCESS) “In 2002, Munk defined an important enigma of 20th century global mean sea-level (GMSL) rise that has yet to be resolved. First, he listed three canonical observations related to Earth’s rotation [(i) the slowing of Earth’s rotation rate over the last three millennia inferred from ancient eclipse observations, and changes in the (ii) amplitude and (iii) orientation of Earth’s rotation vector over the last century estimated from geodetic and astronomic measurements] and argued that they could all be fit by a model of ongoing glacial isostatic adjustment (GIA) associated with the last ice age. Second, he demonstrated that prevailing estimates of the 20th century GMSL rise (~1.5 to 2.0 mm/year), after correction for the maximum signal from ocean thermal expansion, implied mass flux from ice sheets and glaciers at a level that would grossly misfit the residual GIA-corrected observations of Earth’s rotation. We demonstrate that the combination of lower estimates of the 20th century GMSL rise (up to 1990) improved modeling of the GIA process and that the correction of the eclipse record for a signal due to angular momentum exchange between the fluid outer core and the mantle reconciles all three Earth rotation observations. This resolution adds confidence to recent estimates of individual contributions to 20th century sea-level change and to projections of GMSL rise to the end of the 21st century based on them.” Jerry X. Mitrovica, Carling C. Hay, Eric Morrow, Robert E. Kopp, Mathieu Dumberry, Sabine Stanley (2015). Science Advances 11 Dec 2015: Vol. 1, no. 11, e1500679. DOI: 10.1126/sciadv.1500679.

GRACE era secular trends in Earth rotation parameters: A global scale impact of the global warming process? – Roy & Peltier (2011) “Recent trends in the two primary anomalies in the rotational state of the planet are analyzed in detail, namely those associated with the speed and direction of polar wander and with the non-tidal acceleration of the rate of axial rotation (via the measurement of the changing oblateness of the Earth’s shape). It is demonstrated that a significant change in the secular trends in both of these independent parameters became evident subsequent to approximately 1992. It is suggested that both parameters might have come to be substantially influenced by mass loss from both the great polar ice sheets, and from the very large number of small ice-sheets and glaciers that are also being influenced by the global warming phenomenon. The modern values for the secular drifts in those parameters that we estimate are appropriate to the period during which measurements have been made by the satellites of the Gravity Recovery and Climate Experiment (GRACE). These changes in secular rates might greatly assist in understanding why the GRACE-inferred values of the time derivatives of the degree two and order one Stokes coefficients differ so significantly from those associated with Late Quaternary ice-age influence.” Roy, K., and W. R. Peltier (2011), Geophys. Res. Lett., 38, L10306, doi:10.1029/2011GL047282.

Ocean bottom pressure changes lead to a decreasing length-of-day in a warming climate – Landerer et al. (2007) “We use a coupled climate model to evaluate ocean bottom pressure changes in the IPCC-A1B climate scenario. Ocean warming in the 21st and 22nd centuries causes secular oceanic bottom pressure anomalies. The essential feature is a net mass transfer onto shallow shelf areas from the deeper ocean areas, which exhibit negative bottom pressure anomalies. We develop a simple mass redistribution model that explains this mechanism. Regionally, however, distinct patterns of bottom pressure anomalies emerge due to spatially inhomogeneous warming and ocean circulation changes. Most prominently, the Arctic Ocean shelves experience an above-average bottom pressure increase. We find a net transfer of mass from the Southern to the Northern Hemisphere, and a net movement of mass closer towards Earth’s axis of rotation. Thus, ocean warming and the ensuing mass redistribution change the length-of-day by −0.12 ms within 200 years, demonstrating that the oceans are capable of exciting nontidal length-of-day changes on decadal and longer timescales.” Landerer, F. W., J. H. Jungclaus, and J. Marotzke (2007), Geophys. Res. Lett., 34, L06307, doi:10.1029/2006GL029106.

The 60-year solar modulation of global air temperature: the Earth’s rotation and atmospheric circulation connection – Mazzarella (2007) “Spectral analysis of geomagnetic activity, global air temperature, Earth’s rotation rate and zonal circulation, when smoothed from secular trend and periods shorter than 23 years, shows a concentration of energy around the 60-year period explaining more than 80% of the entire variance. This information has enabled the set-up of a cascade physical model that integrates the Sun-atmosphere-Earth system as a single unit and ties solar corpuscular radiation to global warming through Earth’s rotation and atmospheric circulation. Our results suggest that changes in geomagnetic activity, and in the Earth’s rotation, could be used as long- and short-term indicators, respectively, of future changes in global air temperature.” A. Mazzarella, Theoretical and Applied Climatology, Volume 88, Numbers 3-4, 193-199, DOI: 10.1007/s00704-005-0219-z.

Earth rotation/polar motion excitations from atmospheric models – Salstein (2005) “We review both the characteristics of the angular momentum signals that excite Earth rotation variations as calculated from global analyses of the atmosphere, as well as the ability of the current generation of global atmospheric models to simulate such signals. We are interested in results for the planetary axial component, whose fluctuations are related to length of day, and the two equatorial components, related to polar motion. Model results are compared with the analyses of the atmosphere that are produced by weather forecast centers, both contemporaneously and retrospectively, which are also known as operational analyses and reanalyses, repectively. Results from simulations by a group of atmospheric general circulation models forced by time-variable sea surface temperatures over a one- to two-decade period enable us to assess the current state-of-the-art in simulating atmospheric excitations of Earth rotation. These models have become increasingly skillful in this regard on both seasonal and interannual timescales, with much of the latter related to the dominant El Niño-Southern Oscillation atmosphere-ocean signal. Recently, some atmospheric general circulation models have also been run to simulate much of the last century. Several realizations of such a model for a period covering the 20th century, for example, have been used to estimate excitations of the Earth rotation on a number of time scales. Information from all these simulations of the past is useful in the design of atmosphere, or atmosphere-ocean coupled, models that can serve as tools to forecast the future, including those with scenarios of projected increases in greenhouse gases; such models could produce changes in Earth rotation or polar motion parameters.” Salstein, David A., Artificial Satellites – Journal of Planetary Geodesy (ISSN 0208-841X), Vol. 40, No. 1, p. 35 – 46 (2005). In: Proceedings of the seminar “Earth rotation and satellite geodesy from astrometry to GNSS”, Warsaw, September, 18-19, 2003. Part III: Earth rotation.

Low-frequency excitation of length of day and polar motion by the atmosphere – de Viron et al. (2004) “Results of a 100-year run of the Hadley Centre general circulation model are used to compute monthly values of the three components of atmospheric torque on the Earth and of the associated atmospheric angular momentum series. All these results are compared with equivalent ones from the National Center for Environmental Prediction/National Center for Atmospheric Research reanalyses for the overlap period since 1948. We find some important differences; consequently, our results should be taken as an order of magnitude of the effect. We also compute the effect of the atmosphere on length of day (LOD) and polar motion by the use of both the torque and the angular momentum approaches. We find comparable amplitude with both torque and angular momentum for the polar motion; the axial torque, however, related to LOD, appears to be unphysical. The excitation of long-period LOD variation is in phase with the observed variation but much smaller. The low-frequency polar motion is only coherent with the observation at certain particular periods.” de Viron, O., D. Salstein, C. Bizouard, and L. Fernandez (2004), J. Geophys. Res., 109, B03408, doi:10.1029/2003JB002817.

CO2-Induced Changes in Atmospheric Angular Momentum in CMIP2 Experiments – Räisänen (2003) “The response of atmospheric angular momentum to a gradual doubling of CO2 is studied using 16 model experiments participating in the second phase of the Coupled Model Intercomparison Project (CMIP2). The relative angular momentum associated with atmospheric zonal winds increases in all but one of the models, although the magnitude of the change varies widely. About 90% of the 16-model mean increase comes from increasing westerly winds in the stratosphere and the uppermost low-latitude troposphere above 200 hPa. This increase in westerly winds reflects a steepening of the meridional temperature gradient near the tropopause and in the upper troposphere. The simulated temperature gradient at this height increases partly as an indirect consequence of the poleward decrease in the tropopause height, and partly because convection induces a maximum in warming in the tropical upper troposphere. The change in the omega angular momentum associated with the surface pressure distribution is in most models smaller than the change in the relative angular momentum, although its exact value is sensitive to the method of calculation.” Räisänen, Jouni, 2003, J. Climate, 16, 132–143. [Full text]

Unusual Behavior in Atmospheric Angular Momentum during the 1965 and 1972 El Niños – Huang et al. (2003) “The global atmospheric angular momentum (AAM) is known to increase with tropical eastern Pacific sea surface temperature (SST) anomalies during El Niño events. Using a reanalysis dataset, the ratio of the monthly AAM anomaly to El Niño SST anomaly (based on the Niño-3.4 index) is found to be approximately 1 angular momentum unit (=1025 kg m2 s−1) per degree Celsius for most post-1975 El Niños. This ratio is much smaller, however, during the 1965/66 and 1972/73 El Niños, raising the possibilities that either the early reanalysis data are in error due to sparse observations, or the atmospheric response to the two early El Niños was unusual. The possibility of a severe data problem in the reanalysis is ruled out by cross-validating the AAM time series with independent measurements of length of day. The latitudinal structures of the zonal wind anomalies in 1965/66 and 1972/73 are examined for both the reanalysis and a set of general circulation model (GCM) simulations. Multiple GCM runs with specified SST produce a more positive ensemble-mean AAM anomaly in 1965 than its counterpart in the reanalysis. The GCM-simulated ensemble-mean zonal wind anomaly resembles the canonical El Niño response with accelerations of subtropical zonal jets in both hemispheres, a pattern that is almost absent in the reanalysis. On the other hand, a large spread exists among the individual ensemble members in the 1965/66 GCM simulations. Although the majority of the individual ensemble members shows the canonical El Niño response, two outliers (out of 12 runs) exhibit very small zonal wind responses in the Northern Hemisphere similar to the reanalysis. Thus, the observed AAM anomaly during 1965/66 is interpreted as an outlier with atmospheric noise being strong enough to overwhelm the canonical El Niño response. The low AAM in the 1972/73 event is related in the reanalysis to a significantly negative zonal wind response on the equator. This signal is robustly reproduced, although with a slightly smaller amplitude, in the ensemble mean and all individual ensemble members in the GCM simulations. The small ensemble standard deviation and large ensemble-mean response on the equator indicate that the negative response is due to the lower-boundary forcing related to the SST anomaly. The fact that the AAM anomaly in 1972/73 is not well correlated with the Niño-3.4 index, then, indicates that SST anomalies outside the conventional El Niño region may be responsible for the low AAM. The uncharacteristically low values of global AAM in 1965/66 and 1972/73 contribute to a low mean for the decade before 1975, which, combined with high AAM in the post-1980 era, produces a significant upward trend in AAM in the second half of the twentieth century. If the weak AAM anomalies during the two pre-1975 El Niños are due to random noise or incidental non-El Niño influences, taking them at face value would result in an overestimate of about 15%–20% in the multidecadal trend of AAM due to boundary forcing alone. Notably, a multidecadal trend in AAM is also simulated in the ensemble mean of the multiple GCM runs, but its magnitude is smaller than the observed counterpart and more consistent with the multidecadal trend of the Niño-3.4 index. The implications of these findings for climate change detection are discussed.” Huang, Huei-Ping, Klaus M. Weickmann, Richard D. Rosen, 2003, J. Climate, 16, 2526–2539. [Full text]

Recent Earth Oblateness Variations: Unraveling Climate and Postglacial Rebound Effects – Dickey et al. (2002) “Earth’s dynamic oblateness (J 2) has been decreasing due to postglacial rebound (PGR). However, J 2 began to increase in 1997, indicating a pronounced global-scale mass redistribution within Earth’s system. We have determined that the observed increases in J 2 are caused primarily by a recent surge in subpolar glacial melting and by mass shifts in the Southern, Pacific, and Indian oceans. When these effects are removed, the residual trend in J 2 (–2.9 x 10−11 year−1) becomes consistent with previous estimates of PGR from satellite and eclipse data. The climatic significance of these rapid shifts in glacial and oceanic mass, however, remains to be investigated.” Jean O. Dickey, Steven L. Marcus, Olivier de Viron and Ichiro Fukumori, Science 6 December 2002: Vol. 298 no. 5600 pp. 1975-1977, DOI: 10.1126/science.1077777.

Effect of global warming on the length-of-day – Viron et al. (2002) “The anthropogenic increase in greenhouse gas concentrations in the Earth atmosphere will probably induce important modifications of the global circulation in the atmosphere and ocean. Due to the angular momentum conservation of the Earth-atmosphere-ocean system, variation of the length-of-day (LOD) can be expected. By using the outputs of the models participating to the Coupled Model Intercomparison Project (CMIP-2), we reach the following conclusions: (1) the models globally agree to an increase of the LOD of the order of 1 μs/year, (2) the effect is mostly associated with an increase of the mean zonal wind, of which about one third is compensated by a change in mass repartition.” de Viron, O., V. Dehant, H. Goosse, and M. Crucifix (2002), Geophys. Res. Lett., 29(7), 1146, doi:10.1029/2001GL013672.

Ocean angular momentum signals in a climate model and implications for Earth rotation – Ponte et al. (2002) “Estimates of ocean angular momentum (OAM) provide an integrated measure of variability in ocean circulation and mass fields and can be directly related to observed changes in Earth rotation. We use output from a climate model to calculate 240 years of 3-monthly OAM values (two equatorial terms L1 and L2, related to polar motion or wobble, and axial term L3, related to length of day variations) representing the period 1860-2100. Control and forced runs permit the study of the effects of natural and anthropogenically forced climate variability on OAM. All OAM components exhibit a clear annual cycle, with large decadal modulations in amplitude, and also longer period fluctuations, all associated with natural climate variability in the model. Anthropogenically induced signals, inferred from the differences between forced and control runs, include an upward trend in L3, related to inhomogeneous ocean warming and increases in the transport of the Antarctic Circumpolar Current, and a significantly weaker seasonal cycle in L2 in the second half of the record, related primarily to changes in seasonal bottom pressure variability in the Southern Ocean and North Pacific. Variability in mass fields is in general more important to OAM signals than changes in circulation at the seasonal and longer periods analyzed. Relation of OAM signals to changes in surface atmospheric forcing are discussed. The important role of the oceans as an excitation source for the annual, Chandler and Markowitz wobbles, is confirmed. Natural climate variability in OAM and related excitation is likely to measurably affect the Earth rotation, but anthropogenically induced effects are comparatively weak.” R. Ponte, J. Rajamony and J. Gregory, Climate Dynamics, Volume 19, Number 2, 181-190, DOI: 10.1007/s00382-001-0216-6.

Trend in Atmospheric Angular Momentum in a Transient Climate Change Simulation with Greenhouse Gas and Aerosol Forcing – Huang et al. (2001) “The authors investigate the change of atmospheric angular momentum (AAM) in long, transient, coupled atmosphere–ocean model simulations with increasing atmospheric greenhouse gas concentration and sulfate aerosol loading. A significant increase of global AAM, on the order of 4 × 1025 kg m2 s-1 for 3 × CO2–1 × CO2, was simulated by the Canadian Centre for Climate Modelling and Analysis (CCCma) coupled model. The increase was mainly contributed by the relative component of total AAM in the form of an acceleration of zonal mean zonal wind in the tropical–subtropical upper troposphere. Thus, under strong global warming, a superrotational state emerged in the tropical upper troposphere. The trend in zonal mean zonal wind in the meridional plane was characterized by 1) a tropical–subtropical pattern with two maxima near 30° in the upper troposphere, and 2) a tripole pattern in the Southern Hemisphere extending through the entire troposphere and having a positive maximum at 60°S. The implication of the projected increase of global AAM for future changes of the length of day is discussed. The CCCma coupled global warming simulation, like many previous studies, shows a significant increase of tropical SST and includes a zonally asymmetric component that resembles El Niño SST anomalies. In the CCCma transient simulations, even though the tropical SST and global AAM both increased nonlinearly with time, the ratio of their time increments ΔAAM/ΔSST remained approximately constant at about 0.9 × 1025 kg m2 s-1 (°C)-1. This number is close to its counterpart for the observed global AAM response to El Niño. It is suggested that this ratio may be useful as an index for intercomparisons of different coupled model simulations.” Huang, Huei-Ping, Klaus M. Weickmann, C. Juno Hsu, 2001, J. Climate, 14, 1525–1534, doi: 10.1175/1520-0442(2001)0142.0.CO;2. [Full text]

The influence of global warming in Earth rotation speed – del Rio (1999) “The tendency of the atmospheric angular momentum (AAM) is investigated using a 49-year set of monthly AAM data for the period January 1949-December 1997. This data set is constructed with zonal wind values from the reanalyses of NCEP/NCAR, used in conjunction with a variety of operationally produced AAM time series with different independent sources and lengths over 1976-1997. In all the analyzed AAM series the linear trend is found to be positive. Since the angular momentum of the atmosphere-earth system is conserved this corresponds to a net loss of angular momentum by the solid earth, therefore decreasing the Earth rotation speed and increasing the length of day (LOD). The AAM rise is significant to the budget of angular momentum of the global atmosphere-earth system; its value in milliseconds/century (ms/cy) is +0.56 ms/cy, corresponding to one-third of the estimated increase in LOD (+1.7 ms/cy). The major contribution to this secular trend in AAM comes from the equatorial Tropopause. This is consistent with results from a previous study using a simplified aqua-planet model to investigate the AAM variations due to near equatorial warming conditions. During the same time interval, 1949-1997, the global marine + land-surface temperature increases by about 0.79 °C/cy, showing a linear correspondence between surface temperature increase and global AAM of about 0.07 ms per 0.1 °C. These results imply that atmospheric angular momentum may be used as an independent index of the global atmosphere’s dynamical response to the greenhouse forcing, and as such, the length of day may be used as an indirect indicator of global warming.” Abarca del Rio, R., Ann. Geophys., 17, 806-811, doi:10.1007/s00585-999-0806-x, 1999. [Full text]

Response of Zonal Winds and Atmospheric Angular Momentum to a Doubling Of CO2 – Rosen & Gutowski (1992) “The possible impact of doubling CO2 on the zonal-mean zonal winds and the angular momentum of the atmosphere is examined using general circulation model output archived by the Goddard Institute for Space Studies, the National Center for Atmospheric Research, and the Geophysical Fluid Dynamics Laboratory. Whereas the emphasis in most previous studies with these models has been placed on the temperature and precipitation changes expected from a doubled-CO2 scenario, the intent here is to investigate some of the dynamical consequences predicted by them models, especially within the tropics where the zonal-wind and temperature changes are less tightly coupled than elsewhere. Comparisons among the three models of the difference in zonal-mean zonal winds between 2×CO2 and 1×CO2 simulations indicate a common tendency when CO2 is doubled for winds to become more easterly in much of the tropics during June-July-August. Less of a consensus for the tropics emerges for December-January-February, perhaps as a result of differences among the models’ basic climatologies for the zonal-wind field. In general, however, changes predicted for the zonal winds in the tropics and elsewhere are comparable to the interannual variability currently observed, suggesting that these changes ought to become detectable eventually. Largely because of the tropical wind changes, decreases in the troposphere’s relative angular momentum accompany a doubling of CO2 in all the model runs. The amplitude of the decrease is typically a considerable fraction of a model’s seasonal cycle and, in some cases, is large enough that a measurable change in the length of day could result. Although the possibility of an anthropogenic effect on earth’s rotation is noteworthy, such a prediction must be regarded as tentative in light of the shortcomings found in the models’ zonal-wind climatologies and the differences in their zonal-mean responses.” Rosen, Richard D., William J. Gutowski, 1992, J. Climate, 5, 1391–1404. doi: 10.1175/1520-0442(1992)0052.0.CO;2. [Full text]

Global Sea Level and Earth Rotation – Peltier (1988) “Recent analyses of long time scale secular variations of sea level, based on tide gauge observations, have established that sea level is apparently rising at a globally averaged rate somewhat in excess of 1 millimeter per year. It has been suggested that the nonsteric component of this secular rate might be explicable in terms of ongoing mass loss from the small ice sheets and glaciers of the world. Satellite laser ranging and very long baseline interferometry data may be used to deliver strong constraints on this important scenario because of the information that these systems provide on variations of the length of day and of the position of the rotation pole with respect to the earth’s surface geography. These data demonstrate that the hypothesis of mass loss is plausible if the Barents Sea was covered by a substantial ice sheet at the last maximum of the current ice age 18,000 years ago.” W. R. Peltier, Science 13 May 1988: Vol. 240 no. 4854 pp. 895-901, DOI: 10.1126/science.240.4854.895.

An El Niño Signal in Atmospheric Angular Momentum and Earth Rotation – Rosen et al. (1984) “Anomalously high values of atmospheric angular momentum and length of day were observed in late January 1983. This signal in the time series of these two coupled quantities appears to have been a consequence of the equatorial Pacific Ocean warming event of 1982-1983.” Richard D. Rosen, David A. Salstein, T. Marshall Eubanks, Jean O. Dickey and J. Alan Steppe, Science 27 July 1984: Vol. 225 no. 4660 pp. 411-414, DOI: 10.1126/science.225.4660.411.

Atmospheric angular momentum fluctuations and changes in the length of the day – Hide et al. (1980) “Fluctuations in the angular momentum of the Earth’s atmosphere correspond fairly well with equal and opposite fluctuations in the angular momentum of the Earth’s ‘solid’ mantle. A decrease of 20% of the relative angular momentum of the atmosphere during the second half of May 1979 was accompanied by a speeding up of the rotation of the mantle causing the length of the day (l.o.d.) to decrease by 0.6 10-3 s. Although motions in the Earth’s liquid core produce the more pronounced ‘decade’ variations in the l.o.d. there is no evidence that core motions produce l.o.d. variations on much shorter time-scales.” R. Hide, N. T. Birch, L. V. Morrison, D. J. Shea & A. A. White, Nature 286, 114 – 117 (10 July 1980); doi:10.1038/286114a0.

Long Term Variations in the Length of Day and Climatic Change – Lambeck & Cazenave (1976) “The long-period (greater than about 10 yr) variations in the length-of-day (LOD) observed since 1820 show a marked similarity with variations observed in various climatic indices; periods of acceleration of the Earth corresponding to years of increasing intensity of the zonal circulation and to global-surface warming: periods of deceleration corresponding to years of decreasing zonal-circulation intensity and to a global decrease in surface temperatures. The long-period atmospheric excitation functions for near-surface geostrophic winds, for changes in the atmospheric mass distribution and for eustatic variations in sea level have been evaluated and correlate well with the observed changes in the LOD; although their total effect represents only about 10 per cent of the required excitation. The computed excitation lags the LOD variations by about 10–15 yr. Upper atmospheric winds or other meteorological related factors appear to be quite inadequate to provide the additional driving force that is required if the LOD changes are of meteorological origin. Instead, it appears that the LOD fluctuations and the climatic variations on a time scale of 20–30 yr may have a common origin as has been suggested by Anderson. That is, the results suggest that indirect solid Earth effects on climate may be important.” Kurt Lambeck, Amy Cazenave, Geophysical Journal of the Royal Astronomical Society, Volume 46, Issue 3, pages 555–573, September 1976. [Full text]

Posted in AGW evidence | 1 Comment »

New research from last week 20/2011

Posted by Ari Jokimäki on May 23, 2011

Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as they are published. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. Here’s the archive for the news of previous weeks. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news. Planet 3.0 also reports new research.

Published last week:

Earth’s climate doesn’t just revert back to stationary state

Long memory in temperature reconstructions – Rea et al. (2011) “Ever since H. E. Hurst brought the concept of long memory time series to prominence in his study of river flows the origins of the so-called Hurst phenomena have remained elusive. Two sets of competing models have been proposed. The fractional Gaussian noises and their discrete time counter-part, the fractionally integrated processes, possess genuine long memory in the sense that the present state of a system has a temporal dependence on all past states. The alternative to these genuine long memory models are models which are non-stationary in the mean but for physical reasons are constrained to lie in a bounded range, hence on visual inspection appear to be stationary. In these models the long memory is merely an artifact of the method of analysis. There are now a growing number of millenial scale temperature reconstructions available. In this paper we present a new way of looking at long memory in these reconstructions and proxies, which gives support to them being described by the non-stationary models. The implications for climatic change are that the temperature time series are not mean reverting. There is no evidence to support the idea that the observed rise in global temperatures are a natural fluctuation which will reverse in the near future.” William Rea, Marco Reale and Jennifer Brown, Climatic Change, DOI: 10.1007/s10584-011-0068-y.

Swiss increase of downwelling longwave radiation

Trend analysis of surface cloud-free downwelling long-wave radiation from four Swiss sites – Wacker et al. (2011) “We present a trend analysis of surface cloud-free downwelling long-wave radiation provided by pyrgeometer measurements of four stations of the Alpine surface radiation budget network in Switzerland. The stations cover an altitude range between 370 and 3580 meters above sea level. Cloud-free downwelling long-wave radiation, screen-level temperature, and relative humidity were selected from 10 min measurements, and monthly means were calculated. We performed two distinct trend analyses: the annual overall trend was determined applying least squares fitting, whereas nonparametric statistical methods were used to calculate the monthly trends. The cloud-free downwelling long-wave radiation time series shows a consistent and significant increase of 3.5 W m−2 per decade in the last 12 years at all four stations. The monthly trend analysis of the downwelling long-wave radiation revealed trend estimates exceeding the overall trend by a factor of 4 and partly with opposite signs. The monthly trends of the downwelling long-wave radiation are in agreement with the trends observed in screen-level temperature and specific humidity which have been determined using the same statistical methods. By applying a parameterization of cloud-free downwelling long-wave radiation, we quantitatively inferred the causes for the observed cloud-free trends. More than 50% of the downwelling long-wave radiation trends can be explained with the observed variations of temperature and humidity. There is some indication that the radiative effect of high-level clouds has changed and considerably contributed to the downwelling long-wave radiation trends that are not induced by screen-level temperature and humidity.” Wacker, S., J. Gröbner, K. Hocke, N. Kämpfer, and L. Vuilleumier (2011), J. Geophys. Res., 116, D10104, doi:10.1029/2010JD015343.

AMO affects Tibetan Plateau snowfall

Decadal variability in snow cover over the Tibetan Plateau during the last two centuries – Shen et al. (2011) “Based on the coherency in decadal variability between the ice core data and the observed snow cover over the Tibetan Plateau during recent decades, we used three available ice core data to characterize the snow cover variability of the last 200 years. The analysis suggests that the snow cover exhibits significant decadal variability with major shifts around 1840s, 1880s, 1920s, and 1960s. Its variations are found to be closely correlated with the Atlantic Multidecadal Oscillation: Cool/warm phases coincide with large/small snow cover. A plausible mechanism linking the North Atlantic climate to Asian monsoon is presented.” Shen, C., W.-C. Wang, and G. Zeng (2011), Geophys. Res. Lett., 38, L10703, doi:10.1029/2011GL047288.

Increased CO2 affects tropical cyclones

The response of tropical cyclone statistics to an increase in CO2 with fixed sea surface temperatures – Held & Zhao (2011) “The effects on tropical cyclone statistics of doubling CO2, with fixed sea surface temperatures (SSTs), are compared to the effects of a 2K increase in SST, with fixed CO2, using a 50km resolution global atmospheric model. Confirming earlier results of Yoshimura and Sugi (2005), a significant fraction of the reduction in globally averaged tropical storm frequency seen in simulations in which both SST and CO2 are increased can be thought of as the effect of the CO2 increase with fixed SSTs. Globally, the model produces a decrease in tropical cyclone frequency of about 10% due to doubling of CO2 and an additional 10% for a 2K increase in SST, resulting in roughly a 20% reduction when both effects are present. The relative contribution of the CO2 effect to the total reduction is larger in the Northern than in the Southern Hemisphere. The average intensity of storms increases in the model with increasing SST, but intensity remains roughly unchanged, or decreases slightly, with the increase in CO2 alone. As a result, when considering the frequency of more intense cyclones, the intensity increase tends to compensate for the reduced total cyclone numbers for the SST increase in isolation but not for the CO2 increase in isolation. Changes in genesis in these experiments roughly follow changes in mean vertical motion, reflecting changes in convective mass fluxes. Discussion is provided of one possible perspective on how changes in the convective mass flux might alter genesis rates.” Isaac M. Held and Ming Zhao, Journal of Climate 2011, doi: 10.1175/JCLI-D-11-00050.1. [Full text]

Beijing Olympics caused a reduction in aerosols

Reduction of aerosol absorption in Beijing since 2007 from MODIS and AERONET – Lyapustin et al. (2011) “An analysis of the time series of MODIS-based and AERONET aerosol records over Beijing reveals two distinct periods, before and after 2007. The MODIS data from both the Terra and Aqua satellites were processed with the new Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm. A comparison of MAIAC and AERONET AOT shows that whereas MAIAC consistently underestimated peak AOT values by 10–20% in the prior period, the bias mostly disappears after mid-2007. Independent analysis of the AERONET dataset reveals little or no change in the effective radii of the fine and coarse fractions and of the Ångström exponent. At the same time, it shows an increasing trend in the single scattering albedo, by ∼0.02 in 9 years. As MAIAC was using the same aerosol model for the entire 2000–2010 period, the decrease in AOT bias after 2007 can be explained only by a corresponding decrease of aerosol absorption caused by a reduction in local black carbon emissions. The observed changes correlate in time with the Chinese government’s broad measures to improve air quality in Beijing during preparations for the Summer Olympics of 2008.” Lyapustin, A., et al. (2011), Geophys. Res. Lett., 38, L10803, doi:10.1029/2011GL047306.

Antarctic Peninsula warms in observations and models, but why?

Why does the Antarctic Peninsula Warm in climate simulations? – Qu et al. (2011) “The Antarctic Peninsula has warmed significantly since the 1950s. This pronounced and isolated warming trend is collectively captured by 29 twentieth-century climate hindcasts participating in the version 3 Coupled Model Intercomparison Project. To understand the factors driving warming trends in the hindcasts, we examine trends in Peninsula region’s atmospheric heat budget in every simulation. We find that atmospheric latent heat release increases in nearly all hindcasts. These increases are generally anthropogenic in origin, and account for about 60% of the ensemble-mean warming trend in the Peninsula. They are driven primarily by well-understood features of the anthropogenic intensification of global hydrological cycle. As sea surface temperature increases, moisture contained in atmospheric flows increases. When such flows are forced to ascend the Peninsula’s topography, enhanced local latent heat release results. The mechanism driving the warming of the Antarctic Peninsula is therefore clear in the models. Evidence for a similar mechanism operating in the real world is seen in the increasing snow accumulation rates inferred from ice cores drilled in the Peninsula. However, the relative importance of this mechanism and other processes previously identified as potentially causing the observed warming, such as the recent sea ice retreat in the Bellingshausen Sea, is difficult to assess. Thus the relevance of the simulated warming mechanism to the observed warming is unclear, in spite of its robustness in the models.” Xin Qu, Alex Hall and Julien Boé, Climate Dynamics, DOI: 10.1007/s00382-011-1092-3.

Sea level rise might cause extinctions

Sinking ships: conservation options for endemic taxa threatened by sea level rise – Maschinski et al. (2011) “Low-elevation islands face threats from sea level rise (SLR) and increased storm intensity. Evidence of endangered species’ population declines and shifts in vegetation communities are already underway in the Florida Keys. SLR predictions indicate large areas of these habitats may be eliminated in the next century. Using the Florida Keys as a model system, we present a process for evaluating conservation options for rare and endemic taxa. Considering species characteristics and habitat, we assess central issues that influence conservation options. We contrast traditional and controversial options for two animal and two plant species giving special emphasis to perceptions of ecological risk and safety from SLR and suggest courses of action. Multiple strategies will be required to spread extinction risk and will be effective for different time periods. Global climate change presents an uncertain, perhaps no-analog future that will challenge land managers and practitioners to re-evaluate equilibrium-state-conceived laws and policies not only for these taxa, but for many facing similar threats. To embrace conservation in a changing world will require a new dialogue that includes controversial ideas, a review of existing laws and policies, and preparation for the oncoming change.” Joyce Maschinski, Michael S. Ross, Hong Liu, Joe O’Brien, Eric J. von Wettberg and Kristin E. Haskins, Climatic Change, DOI: 10.1007/s10584-011-0083-z.

Vermont Climate Change Indicators

Vermont Climate Change Indicators – Betts (2011) “We develop climate change indicators for Vermont in recent decades based on the trends in freeze dates, the length of the growing season, the frozen period of small lakes, and the onset of spring. These trends, which show a consistent pattern of a warming climate in Vermont during the past fifty years, provide useful information for climate change adaptation planning for the state. The freeze period has got shorter and the growing season for frost-sensitive plants has got longer by about 3.7 (±1.1) days per decade; as the date of the last spring freeze has come earlier by 2.3 (±0.7) days per decade, and the first autumn freeze has come later by 1.5 (±0.8) days per decade. The frozen period for small lakes, which depends on mean temperatures over longer periods, has decreased faster by 6.9 (±1.5) days per decade. Lake freeze-up has occurred later by 3.9 (±1.1) days per decade, while ice-out has come earlier by 2.9 (±1.0) days per decade. Lilac first leaf has also been coming earlier by 2.9 (±0.8) days per decade, while lilac first bloom has advanced more slowly by 1.6 (±0.6) days per decade. The first leaf of Vermont lilacs, an indicator of early spring, is closely correlated with the ice-out of our small reference lake, Stile’s Pond, because both are related to temperatures in March, April and May. In the past forty years, the growing season for frost-sensitive plants has increased by 2 weeks, and the growing season for frost-hardy plants may have increased more.” Alan K. Betts, Weather, Climate, and Society 2011, doi: 10.1175/2011WCAS1096.1. [Full text]

Permafrost role in carbon cycle of glacial cycle

High carbon sequestration in Siberian permafrost loess-paleosols during glacials – Zech et al. (2011) “Recent findings show that the amount of organic carbon stored in high-latitude permafrost regions has been greatly underestimated. While concerns are rising that thawing permafrost and resultant CO2 and methane emissions are a positive feedback mechanism at times of anthropogenic global warming, the potential role of permafrost carbon dynamics on glacial-interglacial timescales has received little attention. Here we present new results from a well-studied permafrost loess-paleosol sequence in north-east Siberia that almost spans two glacial cycles (~220 ka). We analysed the deuterium/hydrogen isotopic ratios (δD) of alkanes, which serve as proxy for paleo-temperature. Thus circumventing difficulties to obtain exact age control for such sequences, the results corroborate our previous notion that more soil organic carbon was sequestered during glacials than during interglacials. This fact highlights the role of permafrost in favouring preservation of soil organic matter. Reduced biomass production during glacials may have been of second-order importance on these timescales. Although future studies are needed to evaluate existing large estimates of carbon dioxide releases from thawing permafrost during the last termination (>1000 Pg C), we suggest that permafrost carbon dynamics contributed to the observed glacial-interglacial variation in atmospheric CO2 and need to be included in carbon cycle and climate models.” Zech, R., Huang, Y., Zech, M., Tarozo, R., and Zech, W., Clim. Past, 7, 501-509, doi:10.5194/cp-7-501-2011, 2011. [Full text]

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Short and long term water vapor feedback

Posted by Ari Jokimäki on May 17, 2011

There’s a lot of discussion on water vapor feedback in different media. Relating to this discussion, I’d like to note an interesting paper which seems to have gone largely unnoticed (also in scientific literature). The paper in question is “An Elicitation of the Dynamic Nature of Water Vapor Feedback in Climate Change Using a 1D Model” by Hallegatte et al. (2006).

Hallegatte et al. are studying the different response times of feedback processes and how they affect the overall water vapor feedback. They say:

Another difficulty in the interpretation of feedback processes arises from the speed of the different responses. Some processes participating in the feedback mechanism may be fast, others may be very slow. This problem is usually avoided by analyzing only the new equilibrium reached by the system after a perturbation has been applied. This current practice might, however, ignore important dynamical components of the response, especially when the forcing is varying.

They study this question with a simple 1D model for atmospheric water vapor. The simplicity of the model of course introduces some uncertainties (they can’t model the dynamic changes for example in Hadley circulation and convection is accounted for only indirectly).

The result of their analysis is shown in the following graph, which shows the evolution of water vapor feedback after a step change in the forcing (doubling of carbon dioxide concentration):

Feedback factor having value below 1 represents negative water vapor feedback. As we can see from the graph, the end result is strongly positive water vapor feedback after 10 years. However, especially noteworthy feature is the apparently negative short-term feedback. It seems that water vapor feedback turns positive only after 2-3 years.

Hallegatte et al. explain this fast negative feedback like this:

The fast pole corresponds to the lowering of latent heat flux due to rainfall decrease, which comes from the rising temperature (corresponding to a decrease in RH). This mechanism constitutes one path of the WV feedback: any transient trajectory showing an increase in atmospheric absolute humidity requires an imbalance between precipitation and evaporation, and hence necessitates an increase in atmospheric latent energy content compared with the equilibrium state. In consequence, the WV feedback process should involve a rapid atmospheric cooling, as formalized in our model, with a time response of about a few weeks.

They also study how the water vapor feedback works for more realistic change in the forcing instead of step change. In this case, the fast negative feedback is hardly detectable, but it only reduces the initial warming a bit.

Their conclusion:

In our model, the WV feedback is found to have a positive static gain of 36%, and a characteristic time longer than 4 yr, making the WV feedback fully active only in response to perturbations that last at least 10 yr.

It seems that based on this study, studying water vapor feedback in the context of anthropogenic global warming should be done in decadal time scales.

Reference: Hallegatte, Stéphane, Alain Lahellec, Jean-Yves Grandpeix, 2006: An Elicitation of the Dynamic Nature of Water Vapor Feedback in Climate Change Using a 1D Model. J. Atmos. Sci., 63, 1878–1894. [abstract, full text]

See also: On quick feedback determinations

Posted in Climate claims, Climate science | 4 Comments »

New research from last week 19/2011

Posted by Ari Jokimäki on May 16, 2011

Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as they are published. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. Here’s the archive for the news of previous weeks. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news. Planet 3.0 also reports new research.

Published last week:

Less temperature stress for rice from global warming

Global warming over the period 1961–2008 did not increase high-temperature stress but did reduce low-temperature stress in irrigated rice across China – Sun & Huang (2011) “Climate change is recognized to increase the frequency and severity of extreme temperature events that lead to declining crop yield, but this impact has not been well evaluated in China. We examined the changes in extreme temperature stress over the past five decades by quantifying the indices of temperature stress (TSI) during different growth stages of irrigated rice across mainland China. Our results suggest that the indices of low- or high-temperature stress can be used to explain the year-to-year changes in rice yield. Analysis using the TSI indicated that low-temperature stress (LTS) in the seedling and heading-flowering stages of single rice in northeast China, the seedling stage of early rice and the heading-flowering stage of late rice in the double rice regions has reduced over the period of 1961–2008. No significant trends in LTS were detected during the booting stage. Moreover, global warming did not enhance high-temperature stress (HTS) in the heading-flowering stage over the same period, except in early rice in the mid-lower Yangtze River Valley where the HTS in the 2000s was higher than in previous decades” Wen Sun and Yao Huang, Agricultural and Forest Meteorology, doi:10.1016/j.agrformet.2011.04.009.

Proxy climate reconstructions from peatlands

Development and refinement of proxy-climate indicators from peats – Chambers et al. (2011) “Peat, especially from acidic mires (bogs), is a natural archive of past environmental change. Reconstructions of past climate from bogs commenced in the 19th Century through examination of visible peat stratigraphy, and later formed the basis for a postglacial climatic scheme widely used in Northwest Europe. Nevertheless, misconceptions as to how bogs grow led to a 50-year lacuna in peatclimate study, before the concept of ‘cyclic regeneration’ in bogs was refuted. In recent decades, research using proxy-climate indicators from bogs has burgeoned. A range of proxies for past hydrological change has been developed, as well as use of pollen, bog oaks and pines and other data to reconstruct past temperatures. Most of this proxy-climate research has been carried out in Northern Europe, but peat-based research in parts of Asia and North America has increased, particularly during the last decade, while research has also been conducted in Australia, New Zealand and South America. This paper reviews developments in proxy-climate reconstructions from peatlands; chronicles use of a range of palaeo-proxies such as visible peat stratigraphy, plant macrofossils, peat humification, testate amoebae and non-pollen palynomorphs; and explains the use of wiggle-match radiocarbon dating and relationship to climate shifts. It details other techniques being used increasingly, such as biomarkers, stable isotopes, inorganic geochemistry and estimation of dust flux; and points to new proxies under development. Although explicit protocols have been developed recently for research on ombrotrophic mires, it must be recognised that not all proxies and techniques have universal applicability, owing to differences in species assemblages, mire formation, topographic controls, and geochemical characteristics.” Frank M. Chambers, Robert K. Booth, Francois De Vleeschouwer, Mariusz Lamentowicz, Gael Le Roux, Dmitri Mauquoy, Jonathan E. Nichols and Bas van Geel, Quaternary International, doi:10.1016/j.quaint.2011.04.039.

Drought affects climate

Drought-associated changes in climate and their relevance for ecosystem experiments and models – De Boeck & Verbeeck (2011) “Drought periods can have important impacts on plant productivity and ecosystem functioning, but climatic conditions other than the lack of precipitation during droughts have never been quantified and have therefore not been considered explicitly in both experimental and modeling studies. Here, we identify which climatic characteristics deviate from normal during droughts and how these deviations could affect plant responses. Analysis of 609 years of daily data from nine Western European meteorological stations reveals that droughts in the studied region are consistently associated with more sunshine (+45 %), increased mean (+1.6 °C) and maximum (+2.8 °C) air temperatures and vapour pressure deficits that were 51 % higher than under normal conditions. These deviations from normal increase significantly as droughts progress. Using the process-model ORCHIDEE, we simulated droughts consistent with the results of the dataset analysis and compared water and carbon exchange of three different vegetation types during such natural droughts and droughts in which only the precipitation was affected. The comparison revealed contrasting responses: carbon loss was higher under natural drought in grasslands, while increased carbon uptake was found especially in decidious forests. This difference was attributed to better access to water reserves in forest ecosystems which prevented drought stress. This demonstrates that the warmer and sunnier conditions naturally associated with droughts can either improve growth or aggravate drought-related stress, depending on water reserves. As the impacts of including or excluding climatic parameters that correlate with drought are substantial, we propose that both experimental and modeling efforts should take into account other environmental factors than merely precipitation.” De Boeck, H. J. and Verbeeck, H., Biogeosciences, 8, 1121-1130, doi:10.5194/bg-8-1121-2011, 2011. [Full text]

Hydrological cycle changes with climate in Tibetan Plateau

Response of hydrological cycle to recent climate changes in the Tibetan Plateau – Yang et al. (2011) “The Tibetan Plateau (TP) surfaces have been experiencing an overall rapid warming and wetting while wind speed and solar radiation have been declining in the last three decades. This study investigated how climate changes influenced the hydrological cycle on the TP during 1984∼2006. To facilitate the analysis, a land surface model was used to simulate surface water budget at all CMA (China Meteorological Administration) stations on the TP. The simulated results were first validated against observed ground temperature and observation-derived heat flux on the western TP and observed discharge trends on the eastern TP. The response of evaporation and runoff to the climate changes was then analyzed. Major finding are as follows. (1) Surface water balance has been changed in recent decades. Observed precipitation shows insignificant increasing trends in central TP and decreasing trends along the TP periphery while evaporation shows overall increasing trends, leading to decreased discharge at major TP water resource areas (semi-humid and humid zones in the eastern and southern TP). (2) At the annual scale, evaporation is water-limited in dry areas and energy-limited (radiation and air temperature) in wet areas; these constraints can be interpreted by the Budyko-curve. Evaporation in autumns and winters was strongly controlled by soil water storage in summers, weakening the dependence of evaporation on precipitation at seasonal scales. (3) There is a complementary effect between the simulated actual evaporation and potential evaporation, but this complementary relationship may deviate from Bouchet’s hypothesis when vapor pressure deficit (or air temperature) is too low, which suppresses the power of vapor transfer.” Kun Yang, Baisheng Ye, Degang Zhou, Bingyi Wu, Thomas Foken, Jun Qin and Zhaoye Zhou, Climatic Change, DOI: 10.1007/s10584-011-0099-4.

Larsen C ice shelf flow increasing

Acceleration and spatial rheology of Larsen C Ice Shelf, Antarctic Peninsula – Khazendar et al. (2011) “The disintegration of several Antarctic Peninsula ice shelves has focused attention on the state of the Larsen C Ice Shelf. Here, we use satellite observations to map ice shelf speed from the years 2000, 2006 and 2008 and apply inverse modeling to examine the spatial pattern of ice-shelf stiffness. Results show that the northern half of the ice shelf has been accelerating since 2000, speeding up by 15% between 2000 and 2006 alone. The distribution of ice stiffness exhibits large spatial variations that we link to tributary glacier flow and fractures. Our results reveal that ice down-flow from promontories is consistently softer, with the exception of Churchill Peninsula where we infer a stabilizing role for marine ice. We conclude that although Larsen C is not facing imminent collapse, it is undergoing significant change in the form of flow acceleration that is spatially related to thinning and fracture.” Khazendar, A., E. Rignot, and E. Larour (2011), Geophys. Res. Lett., 38, L09502, doi:10.1029/2011GL046775.

China’s ecosystems have been global warming sink

Net exchanges of CO2, CH4, and N2O between China’s terrestrial ecosystems and the atmosphere and their contributions to global climate warming – Tian et al. (2011) “China’s terrestrial ecosystems have been recognized as an atmospheric CO2 sink; however, it is uncertain whether this sink can alleviate global warming given the fluxes of CH4 and N2O. In this study, we used a process-based ecosystem model driven by multiple environmental factors to examine the net warming potential resulting from net exchanges of CO2, CH4, and N2O between China’s terrestrial ecosystems and the atmosphere during 1961–2005. In the past 45 years, China’s terrestrial ecosystems were found to sequestrate CO2 at a rate of 179.3 Tg C yr-1 with a 95% confidence range of (62.0 Tg C yr-1, 264.9 Tg C yr-1) while emitting CH4 and N2O at rates of 8.3 Tg C yr-1 with a 95% confidence range of (3.3 Tg C yr-1, 12.4 Tg C yr-1) and 0.6 Tg N yr-1 with a 95% confidence range of (0.2 Tg N yr-1, 1.1 Tg N yr-1), respectively. When translated into global warming potential, it is highly possible that China’s terrestrial ecosystems mitigated global climate warming at a rate of 96.9 Tg CO2eq yr-1 (1 Tg = 1012 g), substantially varying from a source of 766.8 Tg CO2eq yr-1 in 1997 to a sink of 705.2 Tg CO2eq yr-1 in 2002. The southeast and northeast of China slightly contributed to global climate warming; while the northwest, north, and southwest of China imposed cooling effects on the climate system. Paddy land, followed by natural wetland and dry cropland, was the largest contributor to national warming potential; forest, followed by woodland and grassland, played the most significant role in alleviating climate warming. Our simulated results indicate that CH4 and N2O emissions offset approximately 84.8% of terrestrial CO2 sink in China during 1961–2005. This study suggests that the relieving effects of China’s terrestrial ecosystems on climate warming through sequestering CO2 might be gradually offset by increasing N2O emission, in combination with CH4 emission.” Tian, H., X. Xu, C. Lu, M. Liu, W. Ren, G. Chen, J. Melillo, and J. Liu (2011), J. Geophys. Res., 116, G02011, doi:10.1029/2010JG001393.

Cereal harvest dates reveal Chech temperatures

Cereal harvest dates in the Czech Republic between 1501 and 2008 as a proxy for March–June temperature reconstruction – Možný et al. (2011) “Cereal crop harvests reflect the weather patterns of the period immediately preceding them, and thus the dates at which they begin may be used as a source of proxy data on regional climate. Using systematic phenological observations in the Czech Lands (now known as the Czech Republic) after 1845, together with exploration of further surviving documentary evidence (chronicles, diaries, financial accounts etc.), it has proved possible to create series of winter wheat harvest dates for the period 1501–2008. Employing linear regression, the harvesting dates of the main cereal species (wheat, rye, barley, oats) were first converted to winter wheat harvest days and then normalised to the same altitude above sea level. The next step consisted of using series of winter wheat harvest dates to reconstruct mean March–June temperatures in the Czech Republic, applying standard palaeoclimatological methods. Series reconstructed by linear regression explain 70% of temperature variability. A profound cold period corresponding with late winter wheat harvests was noted between 1659 and 1705. In contrast, warm periods (i.e. early winter wheat harvests) were found for the periods of 1517–1542, 1788–1834 and 1946–2008. The period after 1951 is the warmest of all throughout the entire 1501–2008 period. Comparisons with other European temperature reconstructions derived from documentary sources (including grape harvest dates), tree-rings and instrumental data reveal generally close agreement, with significant correlations. Lower correlations around A.D. 1650 and 1750 may be partly related to deterioration of socio-economic conditions in the Czech Lands resulting from prolonged wars. The results obtained demonstrate that it is possible to use widely-available cereal harvest data for climate analysis and also that such data constitute an independent proxy data series for the region of Central Europe crucial to further studies of the potential impact of climatic variability and climate change on agriculture.” Martin Možný, Rudolf Brázdil, Petr Dobrovolný and Mirek Trnka, Climatic Change, DOI: 10.1007/s10584-011-0075-z.

Atmosphere warms, surface winds weaken in tropics

Evidence for a weakening of tropical surface wind extremes in response to atmospheric warming – Gastineau & Soden (2011) “The changes of extreme winds and its links with precipitation are assessed over the past two decades using daily satellite observations and climate model simulations. Both observations and models indicate a decrease in the frequency of the strongest wind events and an increase in the frequency of light wind events in response to a warming of the tropical oceans. The heaviest precipitation events are found to be more frequent when the tropical oceans warm, but the surface winds associated with these extreme rainfall events weaken. These results add further evidence to suggest that the atmospheric circulation becomes less energetic as the climate warms. It further suggests that the enhancement of the extreme precipitation events is mainly a result of increasing atmospheric water vapor and occurs despite a weakening of the large-scale circulation, which acts to diminish the mass convergence toward the precipitating zones.” Gastineau, G., and B. J. Soden (2011), Geophys. Res. Lett., 38, L09706, doi:10.1029/2011GL047138.

Non-clathrate methane pulses during DO-events

Repeated pulses of vertical methane flux recorded in glacial sediments from the southeast Bering Sea – Cook et al. (2011) “There is controversy over the role of marine methane hydrates in atmospheric methane concentrations and climate change during the last glacial period. In this study of two sediment cores from the southeast Bering Sea (700 m and 1467 m water depth), we identify multiple episodes during the last glacial period of intense methane flux reaching the seafloor. Within the uncertainty of the radiocarbon age model, the episodes are contemporaneous in the two cores and have similar timing and duration as Dansgaard-Oeschger events. The episodes are marked by horizons of sediment containing 13C-depleted authigenic carbonate minerals; 13C-depleted archaeal and bacterial lipids, which resemble those found in ANME-1 type anaerobic methane oxidizing microbial consortia; and changes in the abundance and species distribution of benthic foraminifera. The similar timing and isotopic composition of the authigenic carbonates in the two cores is consistent with a region-wide increase in the upward flux of methane bearing fluids. This study is the first observation outside Santa Barbara Basin of pervasive, repeated methane flux in glacial sediments. However, contrary to the “Clathrate Gun Hypothesis” (Kennett et al., 2003), these coring sites are too deep for methane hydrate destabilization to be the cause, implying that a much larger part of the ocean’s sedimentary methane may participate in climate or carbon cycle feedback at millennial timescales. We speculate that pulses of methane in these opal-rich sediments could be caused by the sudden release of overpressure in pore fluids that builds up gradually with silica diagenesis. The release could be triggered by seismic shaking on the Aleutian subduction zone caused by hydrostatic pressure increase associated with sea level rise at the start of interstadials.” Cook, M. S., L. D. Keigwin, D. Birgel, and K.-U. Hinrichs (2011), Paleoceanography, 26, PA2210, doi:10.1029/2010PA001993.

Detecting solar oscillations in global temperature

Empirical Mode Decomposition Applied to Solar Irradiance, Global Temperature, Sunspot Number, and CO2 Concentration Data – Barnhart & Eichinger (2011) “Empirical Mode Decomposition (EMD) is a tool which can decompose and analyze the cyclic components from oscillatory data in the time-domain. When combined with traditional Hilbert spectral analysis, it is similar to spectral tools such as Fourier analysis, wavelet analysis, and generalized time-frequency analysis. However, the EMD method is specifically designed to analyze nonstationary data from nonlinear processes. Fluctuations of total solar irradiance, global temperature, sunspot number, and CO2 concentration are decomposed into their periodic components using the EMD method. The cyclic components of the data are analyzed and compared in the time-domain. An 11-year oscillation in global mean temperature is found and compared with the Schwabe cycle from sunspot and total solar irradiance proxy data. Also, the relative radiative forcing from different periodic components of total solar irradiance and CO2 concentration are empirically estimated.” B.L. Barnhart and W.E. Eichinger, Journal of Atmospheric and Solar-Terrestrial Physics, doi:10.1016/j.jastp.2011.04.012.

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Papers on global vegetation climate feedback

Posted by Ari Jokimäki on May 12, 2011

This is a list of papers on the climate feedback of global vegetation. As the title suggests, emphasis is on global analysis, but papers concerning large regions might also be included. Especially northern parts of the planet are important in this issue. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

Vegetation feedback under future global warming – Jiang et al. (2011) “It has been well documented that vegetation plays an important role in the climate system. However, vegetation is typically kept constant when climate models are used to project anthropogenic climate change under a range of emission scenarios in the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emission Scenarios. Here, an atmospheric general circulation model, and an asynchronously coupled system of an atmospheric and an equilibrium terrestrial biosphere model are forced by monthly sea surface temperature and sea ice extent for the periods 2051–2060 and 2090–2098 as projected with 17 atmosphere–ocean general circulation models participating in the IPCC Fourth Assessment Report, and by appropriate atmospheric carbon dioxide concentrations under the A2 emission scenario. The effects of vegetation feedback under future global warming are then investigated. It is found that the simulated composition and distribution of vegetation during 2051–2060 (2090–2098) differ greatly from the present, and global vegetation tends to become denser as expressed by a 21% (36%) increase in global mean leaf area index, which is most pronounced at the middle and high northern latitudes. Vegetation feedback has little effect on globally averaged surface temperature. On a regional scale, however, it induces statistically significant changes in surface temperature, in particular over most parts of continental Eurasia east of about 60°E where annual surface temperature is expected to increase by 0.1–1.0 K, with an average of about 0.4 K for each future period. These changes can mostly be explained by changes in surface albedo resulting from vegetation changes in the context of future global warming.” Dabang Jiang, Ying Zhang and Xianmei Lang, Theoretical and Applied Climatology, DOI: 10.1007/s00704-011-0428-6.

Impact of vegetation feedback on the temperature and its diurnal range over the Northern Hemisphere during summer in a 2 × CO2 climate – Jeong et al. (2010) “This study examines the potential impact of vegetation feedback on the changes in the diurnal temperature range (DTR) due to the doubling of atmospheric CO2 concentrations during summer over the Northern Hemisphere using a global climate model equipped with a dynamic vegetation model. Results show that CO2 doubling induces significant increases in the daily mean temperature and decreases in DTR regardless of the presence of the vegetation feedback effect. In the presence of vegetation feedback, increase in vegetation productivity related to warm and humid climate lead to (1) an increase in vegetation greenness in the mid-latitude and (2) a greening and the expansion of grasslands and boreal forests into the tundra region in the high latitudes. The greening via vegetation feedback induces contrasting effects on the temperature fields between the mid- and high-latitude regions. In the mid-latitudes, the greening further limits the increase in T max more than T min, resulting in further decreases in DTR because the greening amplifies evapotranspiration and thus cools daytime temperature. The greening in high-latitudes, however, it reinforces the warming by increasing T max more than T min to result in a further increase in DTR from the values obtained without vegetation feedback. This effect on T max and DTR in the high latitude is mainly attributed to the reduction in surface albedo and the subsequent increase in the absorbed insolation. Present study indicates that vegetation feedback can alter the response of the temperature field to increases in CO2 mainly by affecting the T max and that its effect varies with the regional climate characteristics as a function of latitudes.” Su-Jong Jeong, Chang-Hoi Ho, Tae-Won Park, Jinwon Kim and Samuel Levis, Climate Dynamics, DOI: 10.1007/s00382-010-0827-x. [Full text]

Quantifying the negative feedback of vegetation to greenhouse warming: A modeling approach – Bounoua et al. (2010) “Several climate models indicate that in a 2 × CO2 environment, temperature and precipitation would increase and runoff would increase faster than precipitation. These models, however, did not allow the vegetation to increase its leaf density as a response to the physiological effects of increased CO2 and consequent changes in climate. Other assessments included these interactions but did not account for the vegetation down-regulation to reduce plant’s photosynthetic activity and as such resulted in a weak vegetation negative response. When we combine these interactions in climate simulations with 2 × CO2, the associated increase in precipitation contributes primarily to increase evapotranspiration rather than surface runoff, consistent with observations, and results in an additional cooling effect not fully accounted for in previous simulations with elevated CO2. By accelerating the water cycle, this feedback slows but does not alleviate the projected warming, reducing the land surface warming by 0.6°C. Compared to previous studies, these results imply that long term negative feedback from CO2-induced increases in vegetation density could reduce temperature following a stabilization of CO2 concentration.” Bounoua, L., F. G. Hall, P. J. Sellers, A. Kumar, G. J. Collatz, C. J. Tucker, and M. L. Imhoff (2010), Geophys. Res. Lett., 37, L23701, doi:10.1029/2010GL045338. [Full text]

Expansion of the world’s deserts due to vegetation-albedo feedback under global warming – Zeng & Yoon (2009) “Many subtropical regions are expected to become drier due to climate change. This will lead to reduced vegetation which may in turn amplify the initial drying. Using a coupled atmosphere-ocean-land model with a dynamic vegetation component that predicts surface albedo change, here we simulate the climate change from 1901 to 2099 with CO2 and other forcings. In a standard IPCC-style simulation, the model simulated an increase in the world’s ‘warm desert’ area of 2.5 million km2 or 10% at the end of the 21st century. In a more realistic simulation where the vegetation-albedo feedback was allowed to interact, the ‘warm desert’ area expands by 8.5 million km2 or 34%. This occurs mostly as an expansion of the world’s major subtropical deserts such as the Sahara, the Kalahari, the Gobi, and the Great Sandy Desert. It is suggested that vegetation-albedo feedback should be fully included in IPCC future climate projections.” Zeng, N., and J. Yoon (2009), Geophys. Res. Lett., 36, L17401, doi:10.1029/2009GL039699. [Full text]

Global negative vegetation feedback to climate warming responses of leaf litter decomposition rates in cold biomes – Cornelissen et al. (2007) “Whether climate change will turn cold biomes from large long-term carbon sinks into sources is hotly debated because of the great potential for ecosystem-mediated feedbacks to global climate. Critical are the direction, magnitude and generality of climate responses of plant litter decomposition. Here, we present the first quantitative analysis of the major climate-change-related drivers of litter decomposition rates in cold northern biomes worldwide. Leaf litters collected from the predominant species in 33 global change manipulation experiments in circum-arctic-alpine ecosystems were incubated simultaneously in two contrasting arctic life zones. We demonstrate that longer-term, large-scale changes to leaf litter decomposition will be driven primarily by both direct warming effects and concomitant shifts in plant growth form composition, with a much smaller role for changes in litter quality within species. Specifically, the ongoing warming-induced expansion of shrubs with recalcitrant leaf litter across cold biomes would constitute a negative feedback to global warming. Depending on the strength of other (previously reported) positive feedbacks of shrub expansion on soil carbon turnover, this may partly counteract direct warming enhancement of litter decomposition.” Johannes H.C. Cornelissen, Peter M. Van Bodegom, Rien Aerts, Terry V. Callaghan, Richard S.P. Van Logtestijn, Juha Alatalo, F. Stuart Chapin, Renato Gerdol, Jon Gudmundsson, Dylan Gwynn-Jones, Anne E. Hartley, David S. Hik, Annika Hofgaard, Ingibjörg S. Jónsdóttir, Staffan Karlsson, Julia A. Klein, Jim Laundre, Borgthor Magnusson, Anders Michelsen, Ulf Molau, Vladimir G. Onipchenko, Helen M. Quested, Sylvi M. Sandvik, Inger K. Schmidt, Gus R. Shaver, Bjørn Solheim, Nadejda A. Soudzilovskaia, Anna Stenström, Anne Tolvanen, Ørjan Totland, Naoya Wada, Jeffrey M. Welker, Xinquan Zhao, M.O.L. Team, Ecology Letters, Volume 10, Issue 7, pages 619–627, July 2007, DOI: 10.1111/j.1461-0248.2007.01051.x. [Full text]

Assessing Global Vegetation–Climate Feedbacks from Observations – Liu et al. (2006) “The feedback between global vegetation greenness and surface air temperature and precipitation is assessed using remote sensing observations of monthly fraction of photosynthetically active radiation (FPAR) for 1982 to 2000 with a 2.5° grid resolution. Lead/lag correlations are used to infer vegetation–climate interactions. Furthermore, a statistical method is used to quantify the efficiency of vegetation feedback on climate in the observations. This feedback analysis provides a first quantitative assessment of global vegetation feedback on climate. In northern mid- and high latitudes, vegetation variability is found to be driven predominantly by temperature; in the meantime, vegetation also exerts a strong positive feedback on temperature with the feedback accounting for over 10%–25% of the total monthly temperature variance. The strongest positive feedback occurs in the boreal regions of southern Canada/northern United States, northern Europe, and southern Siberia, where the feedback efficiency exceeds 1°C (0.1 FPAR)−1. Over most of the Tropics and subtropics (outside the equatorial rain belt), vegetation is driven primarily by precipitation. However, little vegetation feedback is found on local precipitation when averaged year-round, with the feedback explained variance usually accounting for less than 5% of the total precipitation variance. Nevertheless, in a few isolated small regions such as Northeast Brazil, East Africa, East Asia, and northern Australia, there appears to be some positive vegetation feedback on local precipitation, with the feedback efficiency over 1 cm month−1 (0.1 FPAR)−1. Further studies suggest a significant seasonal variation of the vegetation feedback in some regions. A preliminary analysis also seems to suggest an enhanced intensity of the vegetation feedback, especially on precipitation, at longer time scales and over a larger grid box area. Limitations and implications of the assessment of vegetation feedback are also discussed. The assessed vegetation feedback is shown to be valuable for the evaluation of vegetation–climate feedback in coupled climate–vegetation models.” Liu, Zhengyu, M. Notaro, J. Kutzbach, Naizhuang Liu, 2006, J. Climate, 19, 787–814, doi: 10.1175/JCLI3658.1. [Full text]

Quantifying the effect of vegetation dynamics on the climate of the Last Glacial Maximum – Jahn et al. (2005) “The importance of the biogeophysical atmosphere-vegetation feedback in comparison with the radiative effect of lower atmospheric CO2 concentrations and the presence of ice sheets at the last glacial maximum (LGM) is investigated with the climate system model CLIMBER-2. Equilibrium experiments reveal that most of the global cooling at the LGM (-5.1°C) relative to (natural) present-day conditions is caused by the introduction of ice sheets into the model (-3.0°C), followed by the effect of lower atmospheric CO2 levels at the LGM (-1.5°C), while a synergy between these two factors appears to be very small on global average. The biogeophysical effects of changes in vegetation cover are found to cool the global LGM climate by 0.6°C. The latter are most pronounced in the northern high latitudes, where the taiga-tundra feedback causes annually averaged temperature changes of up to -2.0°C, while the radiative effect of lower atmospheric CO2 in this region only produces a cooling of 1.5°C. Hence, in this region, the temperature changes caused by vegetation dynamics at the LGM exceed the cooling due to lower atmospheric CO2 concentrations.” Jahn, A., Claussen, M., Ganopolski, A., and Brovkin, V., Clim. Past, 1, 1-7, doi:10.5194/cp-1-1-2005, 2005. [Full text]

Coupled atmosphere-ocean-vegetation simulations for modern and mid-Holocene climates: role of extratropical vegetation cover feedbacks – Gallimore et al. et al. (2005) “A full global atmosphere-ocean-land vegetation model is used to examine the coupled climate/vegetation changes in the extratropics between modern and mid-Holocene (6,000 year BP) times and to assess the feedback of vegetation cover changes on the climate response. The model produces a relatively realistic natural vegetation cover and a climate sensitivity comparable to that realized in previous studies. The simulated mid-Holocene climate led to an expansion of boreal forest cover into polar tundra areas (mainly due to increased summer/fall warmth) and an expansion of middle latitude grass cover (due to a combination of enhanced temperature seasonality with cold winters and interior drying of the continents). The simulated poleward expansion of boreal forest and middle latitude expansion of grass cover are consistent with previous modeling studies. The feedback effect of expanding boreal forest in polar latitudes induced a significant spring warming and reduced snow cover that partially countered the response produced by the orbitally induced changes in radiative forcing. The expansion of grass cover in middle latitudes worked to reinforce the orbital forcing by contributing a spring cooling, enhanced snow cover, and a delayed soil water input by snow melt. Locally, summer rains tended to increase (decrease) in areas with greatest tree cover increases (decreases); however, for the broad-scale polar and middle latitude domains the climate responses produced by the changes in vegetation are relatively much smaller in summer/fall than found in previous studies. This study highlights the need to develop a more comprehensive strategy for investigating vegetation feedbacks.” Robert Gallimore, Robert Jacob and John Kutzbach, Climate Dynamics, Volume 25, Numbers 7-8, 755-776, DOI: 10.1007/s00382-005-0054-z. [Full text]

The effect of vegetation on surface temperature: A statistical analysis of NDVI and climate data – Kaufmann et al. (2003) “We use statistical techniques to quantify the effect of interannual variations in vegetation within land covers on surface temperature in North America and Eurasia from satellite measures of surface greenness and ground based meteorological observations. During the winter, reductions in the extent of snow cover cause (in a statistical sense) temperature to rise. During the summer, increases in terrestrial vegetation within land covers cause (in a statistical sense) temperature to fall. Temperature-induced increases in vegetation have slowed increases in surface temperature, but this feedback may be limited by the range over which temperature has a positive effect on vegetation.” Kaufmann, R. K., L. Zhou, R. B. Myneni, C. J. Tucker, D. Slayback, N. V. Shabanov, and J. Pinzon (2003), Geophys. Res. Lett., 30(22), 2147, doi:10.1029/2003GL018251. [Full text]

Green surprise? How terrestrial ecosystems could affect earth’s climate – Foley et al. (2003) “While the earth’s climate can affect the structure and functioning of terrestrial ecosystems, the process also works in reverse. As a result, changes in terrestrial ecosystems may influence climate through both biophysical and biogeochemical processes. This two-way link between the physical climate system and the biosphere is under increasing scrutiny. We review recent developments in the analysis of this interaction, focusing in particular on how alterations in the structure and functioning of terrestrial ecosystems, through either human land-use practices or global climate change, may affect the future of the earth’s climate.” Jonathan A. Foley, Marcos Heil Costa, Christine Delire, Navin Ramankutty, and Peter Snyder. 2003, Frontiers in Ecology and the Environment 1: 38–44, doi:10.1890/1540-9295(2003)001[0038:GSHTEC]2.0.CO;2. [Full text]

Using Satellite Data Assimilation to Infer Global Soil Moisture Status and Vegetation Feedback to Climate – Knorr & Schultz (2003) “The importance of land surface and vegetation characteristics for climate has long been hypothesisized and is reflected by increasingly sophisticated land surface schemesused in climate models. However, accurate parameterisation of land surface processes is still hampered by the complexity of the processes, and by data availability at the global scale required for general circulation models. It is, therefore, desirable to utilise additional data sources for land surface models, of which satellite data appear to be the most promising in terms of availability and spatial and temporal coverage. Here, monthly satellite-derived fields of the fraction of Absorbed Photosynthetically Active Radiation (fAPAR) are assimilated into a land surface and vegetation model, the Biosphere Energy-Transfer Hydrology scheme (BETHY). Assimilation offers the advantage that uncertainties of both the satellite-derived fAPAR and model parameters can be accounted for. Since fAPAR can also be predicted by the model, this information is not discarded as in other approaches where satellite data are used as forcing. During assimilation, a number of model parameters are adjusted until a cost function reaches its minimum. This cost function is defined by the squared deviation between monthly model-simulated and satellite-derived fAPAR as well as between initial and adjusted model parameters, both normalised by their assumed error variances. One of the adjusted parameters, the maximum plant-available soil moisture, is used in a subsequent sensitivity study with the ECHAM-4 climate model. The results show that changes in this parameter as a result of satellite data assimilation can lead to significant changes in simulated soil moisture and 2m air temperature over large parts of the tropics, where soil water storage is usually underestimated in climate and vegetation models. A comparison of BETHY simulations with soil water measurements from Amazonia supports this finding, and also shows that using fAPAR as forcing would have lead to inconsistencies between the carbon balance, predicting a strong decrease in fAPAR at negative carbon gains, and the value of fAPAR prescribed from the satellite data. The study aims at demonstrating the potential of assimilating satellite data into land surface models, as well as the significance of vegetation for the land surface climate. It is further intended to indicate a methodology for the assimilation of satellite data into general circulation models that include an interactive, i.e. climate-responsive, vegetation component.” Wolfgang Knorr and Jan-Peter Schulz, Remote Sensing and Climate Modeling: Synergies and Limitations, Advances in Global Change Research, 2003, Volume 7, 273-306, DOI: 10.1007/0-306-48149-9_12.

Nonlinear Dynamics in a Coupled Vegetation–Atmosphere System and Implications for Desert–Forest Gradient – Zeng et al. (2002) “Although the global vegetation distribution is largely controlled by the large-scale climate pattern, the observed vegetation–rainfall relationship is also influenced by vegetation feedback and climate variability. Using a simplified coupled atmosphere–vegetation model, this work focuses on the effects of these on the gradient of desert–forest transition. A positive feedback from interactive vegetation leads to a wetter and greener state everywhere compared to a state without vegetation. As a result, the gradient in vegetation and rainfall is enhanced at places with moderate rainfall. Climate variability is found to reduce vegetation and rainfall in higher rainfall regions, while enhancing them in lower rainfall regions, thus smoothing out the desert–forest gradient. This latter effect is due to the nonlinear vegetation response to precipitation and it is particularly effective in the savanna regions. The analyses explain results from a three-dimensional climate model. The results suggest that in a varying environment, vegetation plays an active role in determining the observed vegetation–rainfall distributions.” Zeng, Ning, Katrina Hales, J. David Neelin, 2002, J. Climate, 15, 3474–3487, doi: 10.1175/1520-0442(2002)0152.0.CO;2. [Full text]

Sensitivity of Climate to Changes in NDVI – Bounoua et al. (2005) “The sensitivity of global and regional climate to changes in vegetation density is investigated using a coupled biosphere–atmosphere model. The magnitude of the vegetation changes and their spatial distribution are based on natural decadal variability of the normalized difference vegetation index (NDVI). Different scenarios using maximum and minimum vegetation cover were derived from satellite records spanning the period 1982–90. Albedo decreased in the northern latitudes and increased in the Tropics with increased NDVI. The increase in vegetation density revealed that the vegetation’s physiological response was constrained by the limits of the available water resources. The difference between the maximum and minimum vegetation scenarios resulted in a 46% increase in absorbed visible solar radiation and a similar increase in gross photosynthetic CO2 uptake on a global annual basis. This increase caused the canopy transpiration and interception fluxes to increase and reduced those from the soil. The redistribution of the surface energy fluxes substantially reduced the Bowen ratio during the growing season, resulting in cooler and moister near-surface climate, except when soil moisture was limiting. Important effects of increased vegetation on climate are •a cooling of about 1.8 K in the northern latitudes during the growing season and a slight warming during the winter, which is primarily due to the masking of high albedo of snow by a denser canopy; and •a year-round cooling of 0.8 K in the Tropics. These results suggest that increases in vegetation density could partially compensate for parallel increases in greenhouse warming. Increasing vegetation density globally caused both evapotranspiration and precipitation to increase. Evapotranspiration, however, increased more than precipitation, resulting in a global soil-water deficit of about 15%. A spectral analysis on the simulated results showed that changes in the state of vegetation could affect the low-frequency modes of the precipitation distribution and might reduce its low-frequency variability in the Tropics while increasing it in northern latitudes.” Bounoua, L., G. J. Collatz, S. O. Los, P. J. Sellers, D. A. Dazlich, C. J. Tucker, D. A. Randall, 2000, J. Climate, 13, 2277–2292, doi: 10.1175/1520-0442(2000)0132.0.CO;2. [Full text]

Large-Scale Vegetation Feedbacks on a Doubled CO2 Climate – Levis et al. (2000) “Changes in vegetation cover are known to influence the climate system by modifying the radiative, momentum, and hydrologic balance of the land surface. To explore the interactions between terrestrial vegetation and the atmosphere for doubled atmospheric CO2 concentrations, the newly developed fully coupled GENESIS–IBIS climate–vegetation model is used. The simulated climatic response to the radiative and physiological effects of elevated CO2 concentrations, as well as to ensuing simulated shifts in global vegetation patterns is investigated. The radiative effects of elevated CO2 concentrations raise temperatures and intensify the hydrologic cycle on the global scale. In response, soil moisture increases in the mid- and high latitudes by 4% and 5%, respectively. Tropical soil moisture, however, decreases by 5% due to a decrease in precipitation minus evapotranspiration. The direct, physiological response of plants to elevated CO2 generally acts to weaken the earth’s hydrologic cycle by lowering transpiration rates across the globe. Lowering transpiration alone would tend to enhance soil moisture. However, reduced recirculation of water in the atmosphere, which lowers precipitation, leads to more arid conditions overall (simulated global soil moisture decreases by 1%), particularly in the Tropics and midlatitudes. Allowing structural changes in the vegetation cover (in response to changes in climate and CO2 concentrations) overrides the direct physiological effects of CO2 on vegetation in many regions. For example, increased simulated forest cover in the Tropics enhances canopy evapotranspiration overall, offsetting the decreased transpiration due to lower leaf conductance. As a result of increased circulation of moisture through the hydrologic cycle, precipitation increases and soil moisture returns to the value simulated with just the radiative effects of elevated CO2. However, in the highly continental midlatitudes, changes in vegetation cover cause soil moisture to decline by an additional 2%. Here, precipitation does not respond sufficiently to increased plant-water uptake, due to a limited source of external moisture into the region. These results illustrate that vegetation feedbacks may operate differently according to regional characteristics of the climate and vegetation cover. In particular, it is found that CO2 fertilization can cause either an increase or a decrease in available soil moisture, depending on the associated changes in vegetation cover and the ability of the regional climate to recirculate water vapor. This is in direct contrast to the view that CO2 fertilization will enhance soil moisture and runoff across the globe: a view that neglects changes in vegetation structure and local climatic feedbacks.” Levis, Samuel, Jonathan A. Foley, David Pollard, 2000, J. Climate, 13, 1313–1325, doi: 10.1175/1520-0442(2000)0132.0.CO;2. [Full text]

Simulated responses of potential vegetation to doubled-CO2 climate change and feedbacks on near-surface temperature – Betts et al. (2000) “Increases in the atmospheric concentration of carbon dioxide and associated changes in climate may exert large impacts on plant physiology and the density of vegetation cover. These may in turn provide feedbacks on climate through a modification of surface-atmosphere fluxes of energy and moisture. This paper uses asynchronously coupled models of global vegetation and climate to examine the responses of potential vegetation to different aspects of a doubled-CO2 environmental change, and compares the feedbacks on near-surface temperature arising from physiological and structural components of the vegetation response. Stomatal conductance reduces in response to the higher CO2 concentration, but rising temperatures and a redistribution of precipitation also exert significant impacts on this property as well as leading to major changes in potential vegetation structure. Overall, physiological responses act to enhance the warming near the surface, but in many areas this is offset by increases in leaf area resulting from greater precipitation and higher temperatures. Interactions with seasonal snow cover result in a positive feedback on winter warming in the boreal forest regions.” Richard A. Betts, Peter M. Cox, F. Ian Woodward, Global Ecology and Biogeography, Volume 9, Issue 2, pages 171–180, March 2000, DOI: 10.1046/j.1365-2699.2000.00160.x.

Incorporating dynamic vegetation cover within global climate models – Foley et al. (2000) “Numerical models of Earth’s climate system must consider the atmosphere and terrestrial biosphere as a coupled system, with biogeophysical and biogeochemical processes occurring across a range of timescales. On short timescales (i.e., seconds to hours), the coupled system is dominated by the rapid biophysical and biogeochemical processes that exchange energy, water, carbon dioxide, and momentum between the atmosphere and the land surface. Intermediate-timescale (i.e., days to months) processes include changes in the store of soil moisture, changes in carbon allocation, and vegetation phenology (e.g., budburst, leaf-out, senescence, dormancy). On longer timescales (i.e., seasons, years, and decades), there can be fundamental changes in the vegetation structure itself (disturbance, land use, stand growth). In order to consider the full range of coupled atmosphere–biosphere processes, we must extend climate models to include intermediate and long-term ecological phenomena. This paper reviews early attempts at linking climate and equilibrium vegetation models through iterative coupling techniques, and some important insights gained through this procedure. We then summarize recent developments in coupling global vegetation and climate models, and some of the applications of these tools to modeling climate change. Furthermore, we discuss more recent developments in vegetation models (including a new class of models called “dynamic global vegetation models”), and how these models are incorporated with atmospheric general circulation models. Fully coupled climate–vegetation models are still in the very early stages of development. Nevertheless, these prototype models have already indicated the importance of considering vegetation cover as an interactive part of the climate system.” Foley, Jonathan A., Samuel Levis, Marcos Heil Costa, Wolfgang Cramer, and David Pollard. 2000, Ecological Applications 10:1620–1632. [doi:10.1890/1051-0761(2000)010[1620:IDVCWG]2.0.CO;2]. [Full text]

Interactions between the atmosphere and terrestrial ecosystems: influence on weather and climate – Pielke et al. (1998) “This paper overviews the short-term (biophysical) and long-term (out to around 100 year timescales; biogeochemical and biogeographical) influences of the land surface on weather and climate. From our review of the literature, the evidence is convincing that terrestrial ecosystem dynamics on these timescales significantly influence atmospheric processes. In studies of past and possible future climate change, terrestrial ecosystem dynamics are as important as changes in atmospheric dynamics and composition, ocean circulation, ice sheet extent, and orbit perturbations.” Roger A. Pielke, Sr, RonI. Avissar, Michael Raupach, A. Johannes Dolman, Xubin Zeng, A. Scott Denning, Global Change Biology, Volume 4, Issue 5, pages 461–475, June 1998, DOI: 10.1046/j.1365-2486.1998.t01-1-00176.x. [Full text]

Vegetation-climate feedbacks in a greenhouse world – Woodward et al. (1998) “The potential for feedbacks between terrestrial vegetation, climate, and the atmospheric CO2 partial pressure have been addressed by modelling. Previous research has established that under global warming and CO2 enrichment, the stomatal conductance of vegetation tends to decrease, causing a warming effect on top of the driving change in greenhouse warming. At the global scale, this positive feedback is ultimately changed to a negative feedback through changes in vegetation structure. In spatial terms this structural feedback has a variable geographical pattern in terms of magnitude and sign. At high latitudes, increases in vegetation leaf area index (LAI) and vegetation height cause a positive feedback, and warming through reductions in the winter snow–cover albedo. At lower latitudes when vegetation becomes more sparse with warming, the higher albedo of the underlying soil leads to cooling. However, the largest area effects are of negative feedbacks caused by increased evaporative cooling with increasing LAI. These effects do not include feedbacks on the atmospheric CO2 concentration, through changes in the carbon cycle of the vegetation. Modelling experiments, with biogeochemical, physiological and structural feedbacks on atmospheric CO2, but with no changes in precipitation, ocean activity or sea ice formation, have shown that a consequence of the CO2 fertilization effect on vegetation will be a reduction of atmospheric CO2 concentration, in the order of 12% by the year 2100 and a reduced global warming by 0.7°C, in a total greenhouse warming of 3.9°C.” F. I. Woodward, M. R. Lomas and R. A. Betts, Phil. Trans. R. Soc. Lond. B 29 January 1998 vol. 353 no. 1365 29-39, doi: 10.1098/rstb.1998.0188. [Full text]

Coupling dynamic models of climate and vegetation – Foley et al. (1998) “Numerous studies have underscored the importance of terrestrial ecosystems as an integral component of the Earth’s climate system. This realization has already led to efforts to link simple equilibrium vegetation models with Atmospheric General Circulation Models through iterative coupling procedures. While these linked models have pointed to several possible climate–vegetation feedback mechanisms, they have been limited by two shortcomings: (i) they only consider the equilibrium response of vegetation to shifting climatic conditions and therefore cannot be used to explore transient interactions between climate and vegetation; and (ii) the representations of vegetation processes and land-atmosphere exchange processes are still treated by two separate models and, as a result, may contain physical or ecological inconsistencies. Here we present, as a proof concept, a more tightly integrated framework for simulating global climate and vegetation interactions. The prototype coupled model consists of the GENESIS (version 2) Atmospheric General Circulation Model and the IBIS (version 1) Dynamic Global Vegetation Model. The two models are directly coupled through a common treatment of land surface and ecophysiological processes, which is used to calculate the energy, water, carbon, and momentum fluxes between vegetation, soils, and the atmosphere. On one side of the interface, GENESIS simulates the physics and general circulation of the atmosphere. On the other side, IBIS predicts transient changes in the vegetation structure through changes in the carbon balance and competition among plants within terrestrial ecosystems. As an initial test of this modelling framework, we perform a 30 year simulation in which the coupled model is supplied with modern CO2 concentrations, observed ocean temperatures, and modern insolation. In this exploratory study, we run the GENESIS atmospheric model at relatively coarse horizontal resolution (4.5° latitude by 7.5° longitude) and IBIS at moderate resolution (2° latitude by 2° longitude). We initialize the models with globally uniform climatic conditions and the modern distribution of potential vegetation cover. While the simulation does not fully reach equilibrium by the end of the run, several general features of the coupled model behaviour emerge. We compare the results of the coupled model against the observed patterns of modern climate. The model correctly simulates the basic zonal distribution of temperature and precipitation, but several important regional biases remain. In particular, there is a significant warm bias in the high northern latitudes, and cooler than observed conditions over the Himalayas, central South America, and north-central Africa. In terms of precipitation, the model simulates drier than observed conditions in much of South America, equatorial Africa and Indonesia, with wetter than observed conditions in northern Africa and China. Comparing the model results against observed patterns of vegetation cover shows that the general placement of forests and grasslands is roughly captured by the model. In addition, the model simulates a roughly correct separation of evergreen and deciduous forests in the tropical, temperate and boreal zones. However, the general patterns of global vegetation cover are only approximately correct: there are still significant regional biases in the simulation. In particular, forest cover is not simulated correctly in large portions of central Canada and southern South America, and grasslands extend too far into northern Africa. These preliminary results demonstrate the feasibility of coupling climate models with fully dynamic representations of the terrestrial biosphere. Continued development of fully coupled climate-vegetation models will facilitate the exploration of a broad range of global change issues, including the potential role of vegetation feedbacks within the climate system, and the impact of climate variability and transient climate change on the terrestrial biosphere.” Jonathan A. Foley, Samuel Levis, I. Colin Prentice, David Pollard, Starley L. Thompson, Global Change Biology, Volume 4, Issue 5, pages 561–579, June 1998, DOI: 10.1046/j.1365-2486.1998.t01-1-00168.x. [Full text]

The Influence of Vegetation-Atmosphere-Ocean Interaction on Climate During the Mid-Holocene – Ganopolski et al. (1998) “Simulations with a synchronously coupled atmosphere–ocean–vegetation model show that changes in vegetation cover during the mid-Holocene, some 6000 years ago, modify and amplify the climate system response to an enhanced seasonal cycle of solar insolation in the Northern Hemisphere both directly (primarily through the changes in surface albedo) and indirectly (through changes in oceanic temperature, sea-ice cover, and oceanic circulation). The model results indicate strong synergistic effects of changes in vegetation cover, ocean temperature, and sea ice at boreal latitudes, but in the subtropics, the atmosphere–vegetation feedback is most important. Moreover, a reduction of the thermohaline circulation in the Atlantic Ocean leads to a warming of the Southern Hemisphere.” Andrey Ganopolski, Claudia Kubatzki, Martin Claussen, Victor Brovkin and Vladimir Petoukhov, Science 19 June 1998: Vol. 280 no. 5371 pp. 1916-1919, DOI: 10.1126/science.280.5371.1916. [Full text]

Potential role of vegetation feedback in the climate sensitivity of high-latitude regions: A case study at 6000 years B.P. – TEMPO (1996) “Previous climate model simulations have shown that the configuration of the Earth’s orbit during the early to mid-Holocene (approximately 10–5 kyr) can account for the generally warmer-than-present conditions experienced by the high latitudes of the northern hemisphere. New simulations for 6 kyr with two atmospheric/mixed-layer ocean models (Community Climate Model, version 1, CCMl, and Global ENvironmental and Ecological Simulation of Interactive Systems, version 2, GENESIS 2) are presented here and compared with results from two previous simulations with GENESIS 1 that were obtained with and without the albedo feedback due to climate-induced poleward expansion of the boreal forest. The climate model results are summarized in the form of potential vegetation maps obtained with the global BIOME model, which facilitates visual comparisons both among models and with pollen and plant macrofossil data recording shifts of the forest-tundra boundary. A preliminary synthesis shows that the forest limit was shifted 100–200 km north in most sectors. Both CCMl and GENESIS 2 produced a shift of this magnitude. GENESIS 1 however produced too small a shift, except when the boreal forest albedo feedback was included. The feedback in this case was estimated to have amplified forest expansion by approximately 50%. The forest limit changes also show meridional patterns (greatest expansion in central Siberia and little or none in Alaska and Labrador) which have yet to be reproduced by models. Further progress in understanding of the processes involved in the response of climate and vegetation to orbital forcing will require both the deployment of coupled atmosphere-biosphere-ocean models and the development of more comprehensive observational data sets.” TEMPO (1996), Global Biogeochem. Cycles, 10(4), 727–736, doi:10.1029/96GB02690.

Role of orbitally induced changes in tundra area in the onset of glaciation – Gallimore & Kutzbach (1996) “THE link between glacial–interglacial cycles and changes in insolation due to variations in the Earth’s orbital parameters is well established. But of the attempts to simulate incipient glaciation using three-dimensional general circulation models (GCMs) driven by orbital forcing alone, only one has been successful. GCM experiments show that reduced summer insolation 115,000 years ago (during an interglacial-to-glacial climate shift) produces sufficient high-latitude cooling to cause expansion of tundra at the expense of boreal forest, which in turn can induce more cooling. Here we show, using a global climate model, that the increase in surface albedo (under snow-covered conditions) that results from a biome model estimate of tundra expansion 115,000 years ago is sufficient to induce glaciation over extreme-northeastern Canada. If the additional cooling from this estimated tundra expansion induces further expansion, then widespread glaciation occurs at latitudes above 65° N. These results suggest that the climate feedback from high-latitude tundra expansion might have contributed to the onset of the most recent glaciation.” R. G. Gallimore & J. E. Kutzbach, Nature 381, 503 – 505 (06 June 1996); doi:10.1038/381503a0. [Full text]

An integrated biosphere model of land surface processes, terrestrial carbon balance, and vegetation dynamics – Foley et al. (1996) “Here we present a new terrestrial biosphere model (the Integrated Biosphere Simulator – IBIS) which demonstrates how land surface biophysics, terrestrial carbon fluxes, and global vegetation dynamics can be represented in a single, physically consistent modeling framework. In order to integrate a wide range of biophysical, physiological, and ecological processes, the model is designed around a hierarchical, modular structure and uses a common state description throughout. First, a coupled simulation of the surface water, energy, and carbon fluxes is performed on hourly timesteps and is integrated over the year to estimate the annual water and carbon balance. Next, the annual carbon balance is used to predict changes in the leaf area index and biomass for each of nine plant functional types, which compete for light and water using different ecological strategies. The resulting patterns of annual evapotranspiration, runoff, and net primary productivity are in good agreement with observations. In addition, the model simulates patterns of vegetation dynamics that qualitatively agree with features of the natural process of secondary succession. Comparison of the model’s inferred near-equilibrium vegetation categories with a potential natural vegetation map shows a fair degree of agreement. This integrated modeling framework provides a means of simulating both rapid biophysical processes and long-term ecosystem dynamics that can be directly incorporated within atmospheric models.” Foley, J. A., I. C. Prentice, N. Ramankutty, S. Levis, D. Pollard, S. Sitch, and A. Haxeltine (1996), Global Biogeochem. Cycles, 10(4), 603–628, doi:10.1029/96GB02692. [Full text]

Effects of boreal forest vegetation on global climate – Bonan et al. (1992) “TERRESTRIAL ecosystems are thought to play an important role in determining regional and global climate1–6; one example of this is in Amazonia, where destruction of the tropical rainforest leads to warmer and drier conditions4–6. Boreal forest ecosystems may also affect climate. As temperatures rise, the amount of continental and oceanic snow and ice is reduced, so the land and ocean surfaces absorb greater amounts of solar radiation, reinforcing the warming in a ‘snow/ice/albedo’ feedback which results in large climate sensitivity to radiative forcings7–9. This sensitivity is moderated, however, by the presence of trees in northern latitudes, which mask the high reflectance of snow10,11, leading to warmer winter temperatures than if trees were not present12–14. Here we present results from a global climate model which show that the boreal forest warms both winter and summer air temperatures, relative to simulations in which the forest is replaced with bare ground or tundra vegetation. Our results suggest that future redistributions of boreal forest and tundra vegetation (due, for example, to extensive logging, or the influence of global warming) could initiate important climate feedbacks, which could also extend to lower latitudes.” Gordon B. Bonan, David Pollard & Starley L. Thompson, Nature 359, 716 – 718 (22 October 1992); doi:10.1038/359716a0.

Influence of Land-Surface Evapotranspiration on the Earth’s Climate – Shukla & Mintz (1982) “Calculations with a numerical model of the atmosphere show that the global fields of rainfall, temperature, and motion strongly depend on the land- surface evapotranspiration. This confirms the long-held idea that the surface vegetation, which produces the evapotransporation, is an important factor in the earth’s climate.” J. Shukla and Y. Mintz, Science 19 March 1982: Vol. 215 no. 4539 pp. 1498-1501, DOI: 10.1126/science.215.4539.1498.

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New research from last week 18/2011

Posted by Ari Jokimäki on May 9, 2011

Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as they are published. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. Here’s the archive for the news of previous weeks. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news. Planet 3.0 also reports new research.

Published last week:

Evidence for strengthening of tropical hydrological cycle

Recent trends of the tropical hydrological cycle inferred from Global Precipitation Climatology Project and International Satellite Cloud Climatology Project data – Zhou et al. (2011) “Scores of modeling studies have shown that increasing greenhouse gases in the atmosphere impact the global hydrologic cycle; however, disagreements on regional scales are large, and thus the simulated trends of such impacts, even for regions as large as the tropics, remain uncertain. The present investigation attempts to examine such trends in the observations using satellite data products comprising Global Precipitation Climatology Project precipitation and International Satellite Cloud Climatology Project cloud and radiation. Specifically, evolving trends of the tropical hydrological cycle over the last 20–30 years were identified and analyzed. The results show (1) intensification of tropical precipitation in the rising regions of the Walker and Hadley circulations and weakening over the sinking regions of the associated overturning circulation; (2) poleward shift of the subtropical dry zones (up to 2° decade−1 in June-July-August (JJA) in the Northern Hemisphere and 0.3–0.7° decade−1 in June-July-August and September-October-November in the Southern Hemisphere) consistent with an overall broadening of the Hadley circulation; and (3) significant poleward migration (0.9–1.7° decade−1) of cloud boundaries of Hadley cell and plausible narrowing of the high cloudiness in the Intertropical Convergence Zone region in some seasons. These results support findings of some of the previous studies that showed strengthening of the tropical hydrological cycle and expansion of the Hadley cell that are potentially related to the recent global warming trends.” Zhou, Y. P., K.-M. Xu, Y. C. Sud, and A. K. Betts (2011), J. Geophys. Res., 116, D09101, doi:10.1029/2010JD015197. [Full text]

More research on Forbush decrease effects

Forbush decreases, solar irradiance variations, and anomalous cloud changes – Laken et al. (2011) “Changes in the galactic cosmic ray (GCR) flux due to variations in solar activity may provide an indirect connection between the Sun’s and the Earth’s climates. Epoch superpositional (composite) analyses of high-magnitude GCR fluctuations, known as Forbush decrease (FD) events, have been widely used to test this hypothesis, with varied results. This work provides new information regarding the interpretation of this approach, suggesting that FD events do not isolate the impacts of GCR variations from those of solar irradiance changes. On average, irradiance changes of ∼0.4 W m−2 outside the atmosphere occur around 2 days in advance of FD-associated GCR decreases. Using this 2 day gap to separate the effects of irradiance variations from GCR variations on cloud cover, we demonstrate small, but statistically significant, anomalous cloud changes occurring only over areas of the Antarctic plateau in association with the irradiance changes, which previous workers had attributed to GCR variations. Further analysis of the sample shows that these cloud anomalies occurred primarily during polar darkness, precluding the possibility of a causal link to a direct total solar irradiance effect. This work suggests that previous FD-based studies may have ineffectively isolated the impacts of GCR variations on the Earth’s atmosphere.” Laken, B., D. Kniveton, and A. Wolfendale (2011), J. Geophys. Res., 116, D09201, doi:10.1029/2010JD014900.

First signature of rebound in Antarctic ozone

Rebound of Antarctic ozone – Salby et al. (2011) “Restrictions on CFCs have led to a gradual decline of Equivalent Effective Stratospheric Chlorine (EESC). A rebound of Antarctic ozone, however, has remained elusive, masked by large interannual changes that dominate its current evolution. A positive response of ozone is not expected to emerge for at least 1–2 decades, possibly not for half a century. We show that interannual changes of the Antarctic ozone hole are accounted for almost perfectly by changes in dynamical forcing of the stratosphere. The close relationship enables dynamically-induced changes of ozone to be removed, unmasking the climate signal associated with CFCs. The component independent of dynamically-induced changes exhibits a clear upward trend over the last decade – the first signature of a rebound in Antarctic ozone. It enables ozone to be tracked relative to CFCs and other changes of climate.” Salby, M., E. Titova, and L. Deschamps (2011), Geophys. Res. Lett., 38, L09702, doi:10.1029/2011GL047266.

Yet another confirmation of increased Greenland ice sheet melt

Melting trends over the Greenland ice sheet (1958–2009) from spaceborne microwave data and regional climate models – Fettweis et al. (2011) “To study near-surface melt changes over the Greenland ice sheet (GrIS) since 1979, melt extent estimates from two regional climate models were compared with those obtained from spaceborne microwave brightness temperatures using two different remote sensing algorithms. The results from the two models were consistent with those obtained with the remote sensing algorithms at both daily and yearly time scales, encouraging the use of the models for analyzing melting trends before the satellite era (1958–1979), when forcing data is available. Differences between satellite-derived and model-simulated results still occur and are used here to identify (i) biases in the snow models (notably in the albedo parametrization, in the thickness of a snow layer, in the maximum liquid water content within the snowpack and in the snowfall impacting the bare ice appearance in summer) and (ii) limitations in the use of passive microwave data for snowmelt detection at the edge of the ice sheet due to mixed pixel effect (e.g., tundra or rock nearby the ice sheet). The results from models and spaceborne microwave sensors confirm a significant (p-value = 0.01) increase in GrIS surface melting since 1979. The melt extent recorded over the last years (1998, 2003, 2005 and 2007) is unprecedented in the last 50 yr with the cumulated melt area in the 2000’s being, on the average, twice that of the 1980’s.” Fettweis, X., Tedesco, M., van den Broeke, M., and Ettema, J., The Cryosphere, 5, 359-375, doi:10.5194/tc-5-359-2011, 2011.

Storm track cloudiness shifts poleward -> positive cloud feedback

Changes in extratropical storm track cloudiness 1983–2008: observational support for a poleward shift – Bender et al. (2011) “Climate model simulations suggest that the extratropical storm tracks will shift poleward as a consequence of global warming. In this study the northern and southern hemisphere storm tracks over the Pacific and Atlantic ocean basins are studied using observational data, primarily from the International Satellite Cloud Climatology Project, ISCCP. Potential shifts in the storm tracks are examined using the observed cloud structures as proxies for cyclone activity. Different data analysis methods are employed, with the objective to address difficulties and uncertainties in using ISCCP data for regional trend analysis. In particular, three data filtering techniques are explored; excluding specific problematic regions from the analysis, regressing out a spurious viewing geometry effect, and excluding specific cloud types from the analysis. These adjustments all, to varying degree, moderate the cloud trends in the original data but leave the qualitative aspects of those trends largely unaffected. Therefore, our analysis suggests that ISCCP data can be used to interpret regional trends in cloudiness, provided that data and instrumental artefacts are recognized and accounted for. The variation in magnitude between trends emerging from application of different data correction methods, allows us to estimate possible ranges for the observational changes. It is found that the storm tracks, here represented by the extent of the midlatitude-centered band of maximum cloud cover over the studied ocean basins, experience a poleward shift as well as a narrowing over the 25 year period covered by ISCCP. The observed magnitudes of these effects are larger than in current generation climate models (CMIP3). The magnitude of the shift is particularly large in the northern hemisphere Atlantic. This is also the one of the four regions in which imperfect data primarily prevents us from drawing firm conclusions. The shifted path and reduced extent of the storm track cloudiness is accompanied by a regional reduction in total cloud cover. This decrease in cloudiness can primarily be ascribed to low level clouds, whereas the upper level cloud fraction actually increases, according to ISCCP. Independent satellite observations of radiative fluxes at the top of the atmosphere are consistent with the changes in total cloud cover. The shift in cloudiness is also supported by a shift in central position of the mid-troposphere meridional temperature gradient. We do not find support for aerosols playing a significant role in the satellite observed changes in cloudiness. The observed changes in storm track cloudiness can be related to local cloud-induced changes in radiative forcing, using ERBE and CERES radiative fluxes. The shortwave and the longwave components are found to act together, leading to a positive (warming) net radiative effect in response to the cloud changes in the storm track regions, indicative of positive cloud feedback. Among the CMIP3 models that simulate poleward shifts in all four storm track areas, all but one show decreasing cloud amount on a global mean scale in response to increased CO2 forcing, further consistent with positive cloud feedback. Models with low equilibrium climate sensitivity to a lesser extent than higher-sensitivity models simulate a poleward shift of the storm tracks.” Frida A-M. Bender, V. Ramanathan and George Tselioudis, Climate Dynamics, DOI: 10.1007/s00382-011-1065-6.

Role of celebrities in climate change communication

Sources, media, and modes of climate change communication: the role of celebrities – Anderson (2011) “This article reviews existing research on the portrayal of climate change within the print media, paying particular attention to the increasing role that celebrities have come to play within popular culture. While this is certainly not a new development, celebrities are increasingly appearing as key voices within the climate change debate, providing a powerful news hook and potential mobilizing agent. Early coverage of climate change was dominated by scientific sources, but as the debate became more institutionalized and politicized a wider variety of competing sources entered the news arena. Yet media prominence is not necessarily a reliable indicator of influence. How issues are framed is of crucial importance and celebrity interventions can be a double-edged sword.” Alison Anderson, Wiley Interdisciplinary Reviews: Climate Change, DOI: 10.1002/wcc.119.

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New research from last week 17/2011

Posted by Ari Jokimäki on May 2, 2011

Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as they are published. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. Here’s the archive for the news of previous weeks. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news. Planet 3.0 also reports new research.

Published last week:

Good news! Global warming improves fossil preservation

Exceptional fossil preservation during CO2 greenhouse crises? – Retallack (2011) “Exceptional fossil preservation may require not only exceptional places, but exceptional times, as demonstrated here by two distinct types of analysis. First, irregular stratigraphic spacing of horizons yielding articulated Triassic fishes and Cambrian trilobites is highly correlated in sequences in different parts of the world, as if there were short temporal intervals of exceptional preservation globally. Second, compilations of ages of well-dated fossil localities show spikes of abundance which coincide with stage boundaries, mass extinctions, oceanic anoxic events, carbon isotope anomalies, spikes of high atmospheric carbon dioxide, and transient warm-wet paleoclimates. Exceptional fossil preservation may have been promoted during unusual times, comparable with the present: CO2 greenhouse crises of expanding marine dead zones, oceanic acidification, coral bleaching, wetland eutrophication, sea level rise, ice-cap melting, and biotic invasions.” Gregory J. Retallack, Palaeogeography, Palaeoclimatology, Palaeoecology, doi:10.1016/j.palaeo.2011.04.023.

Temperature extremes in China since 1960

Observed changes of temperature extremes during 1960–2005 in China: natural or human-induced variations? – Zhang et al. (2011) “The purpose of this study was to statistically examine changes of surface air temperature in time and space and to analyze two factors potentially influencing air temperature changes in China, i.e., urbanization and net solar radiation. Trends within the temperature series were detected by using Mann-Kendall trend test technique. The scientific problem this study expected to address was that what could be the role of human activities in the changes of temperature extremes. Other influencing factors such as net solar radiation were also discussed. The results of this study indicated that: (1) increasing temperature was observed mainly in the northeast and northwest China; (2) different behaviors were identified in the changes of maximum and minimum temperature respectively. Maximum temperature seemed to be more influenced by urbanization, which could be due to increasing urban albedo, aerosol, and air pollutions in the urbanized areas. Minimum temperature was subject to influences of variations of net solar radiation; (3) not significant increasing and even decreasing temperature extremes in the Yangtze River basin and the regions south to the Yangtze River basin could be the consequences of higher relative humidity as a result of increasing precipitation; (4) the entire China was dominated by increasing minimum temperature. Thus, we can say that the warming process of China was reflected mainly by increasing minimum temperature. In addition, consistently increasing temperature was found in the upper reaches of the Yellow River basin, the Yangtze River basin, which have the potential to enhance the melting of permafrost in these areas. This may trigger new ecological problems and raise new challenges for the river basin scale water resource management.” Qiang Zhang, Jianfeng Li, Yongqin David Chen and Xiaohong Chen, Theoretical and Applied Climatology, DOI: 10.1007/s00704-011-0447-3.

Analysis of Russian 2010 heatwave

The Central European and Russian Heat Event of July-August 2010 – Grumm (2011) No abstract. “This paper will document the large scale conditions associated with the eastern European and Russian heat wave of July-August 2010. The focus is on an analysis of anomalies associated with key features.” Richard H. Grumm, Bulletin of the American Meteorological Society 2011, doi: 10.1175/2011BAMS3174.1. [Full text]

Tree species among saplings change with global warming

Changes in tree sapling composition within powerline corridors appear to be consistent with climatic changes in New York State – Treyger & Nowak (2011) “Despite emerging evidence that on-going climate change is affecting species physiology, distribution, and phenology, there are few studies that examine changes in tree sapling establishment as a response. Changes in tree species composition can be expected due to increasing temperatures, with subsequent effects on future forest compositions. This study’s objective was to examine changes in relative density of tree species assemblages within powerline corridors from 1975–2003 in New York State. Powerline corridors in New York are commonly surrounded by forests, which creates constant tree invasion pressure within a perpetual old-field environment. This unique combination of factors allowed us to examine tree sapling establishment in a nearly constant environment over a 28-year period, utilizing manova and PCA as primary statistical analyses. Tree species dynamics varied across the four ecological provinces within New York over time. Northern pioneer species (Betula populifolia, Fraxinus americana, Prunus serotina, and Tilia americana) declined across the state over the past 28 years, while the southern pioneer species (Betula lenta, Liriodendron tulipifera, and Sassafras albidum) increased in the hot continental division. In the warm continental division, the pine-hemlock assemblage increased in the Northeastern Mixed Forest Province, while aspen-birch increased in the Adirondack Highlands Forest Province, likely due to increases in precipitation. It appears that climate change may have had some influence on tree sapling composition that could affect future vegetation management decisions and expectations in powerline rights-of-way and forests.” Artem L. Treyger, Christopher A. Nowak, Global Change Biology, DOI: 10.1111/j.1365-2486.2011.02455.x.

Even in warming world there will be extreme cold events

Persisting cold extremes under 21st-century warming scenarios – Kodra et al. (2011) “Analyses of climate model simulations and observations reveal that extreme cold events are likely to persist across each land-continent even under 21st-century warming scenarios. The grid-based intensity, duration and frequency of cold extreme events are calculated annually through three indices: the coldest annual consecutive three-day average of daily maximum temperature, the annual maximum of consecutive frost days, and the total number of frost days. Nine global climate models forced with a moderate greenhouse-gas emissions scenario compares the indices over 2091–2100 versus 1991–2000. The credibility of model-simulated cold extremes is evaluated through both bias scores relative to reanalysis data in the past and multi-model agreement in the future. The number of times the value of each annual index in 2091–2100 exceeds the decadal average of the corresponding index in 1991–2000 is counted. The results indicate that intensity and duration of grid-based cold extremes, when viewed as a global total, will often be as severe as current typical conditions in many regions, but the corresponding frequency does not show this persistence. While the models agree on the projected persistence of cold extremes in terms of global counts, regionally, inter-model variability and disparity in model performance tends to dominate. Our findings suggest that, despite a general warming trend, regional preparedness for extreme cold events cannot be compromised even towards the end of the century.” Kodra, E., K. Steinhaeuser, and A. R. Ganguly (2011), Persisting cold extremes under 21st-century warming scenarios, Geophys. Res. Lett., 38, L08705, doi:10.1029/2011GL047103.

Future of snow in North-Europe

21st Century changes in snow climate in Northern Europe: a high-resolution view from ENSEMBLES regional climate models – Räisänen & Eklund (2011) “Changes in snow amount in northern Europe are analysed from 11 regional model simulations of 21st century climate under the Special Report on Emissions Scenarios A1B scenario. These high-resolution models collectively indicate a future decrease in the water equivalent of the snow pack (SWE). Although winter precipitation increases, this is insufficient to compensate for the increased fraction of liquid precipitation and increased snowmelt caused by higher temperatures. The multi-model mean results suggest a slight increase in March mean SWE only locally in mountains of northern Sweden, and even there, snow is reduced earlier in winter and later in spring. The nature of the changes remains the same throughout the 21st century, but their magnitude increases with time as the greenhouse gas forcing grows larger. The geographical patterns of the change support the physically intuitive view that snow is most vulnerable to warming in areas with relatively mild winter climate. A similar relationship emerges when comparing the 11 simulations with each other: the ratio between the relative SWE decrease and winter mean temperature change is larger (smaller) for simulations with higher (lower) late 20th century winter temperatures. Despite the decrease in long-term mean SWE, individual snow-rich winters do occur in the simulations, but they become increasingly uncommon towards the end of the 21st century.” Jouni Räisänen and Joonas Eklund, Climate Dynamics, DOI: 10.1007/s00382-011-1076-3.

When sea level rises, rice price rises

Climate change, sea level rise and rice: global market implications – Chen et al. (2011) “Climate change will influence yields while sea level rise can inundate producing lands. The research reported investigates the individual and simultaneous effects of these factors on production, trade and consumption of rice the world’s number one food crop. A global rice trade model is utilized to do this. The results indicate that the combination of yield and sea level effects causes a significant reduction in production and an increase in rice prices which may have important policy implications for food security. Global rice production is reduced by 1.60% to 2.73% while global rice price increases by 7.14% to 12.77%. Sea level rise is particularly a risk factor in Bangladesh, Japan, Taiwan, Egypt, Myanmar and Vietnam. In the face of such developments, adaptation may well be desirable and thus an investigation is done over adaptation options of increased technical progress or trade liberalization with the results showing that both can mitigate such damages.” Chi-Chung Chen, Bruce McCarl and Ching-Cheng Chang, Climatic Change, DOI: 10.1007/s10584-011-0074-0.

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