AGW Observer

Observations of anthropogenic global warming

New research from last week 50/2012

Posted by Ari Jokimäki on December 17, 2012

These weekly new research posts will not be published anymore after the end of this year. New research will be communicated in some different format in the future. We are working on it in Skeptical Science author community. I’m not yet sure how this might affect my output in my Facebook and Twitter pages, but it is probable that number of papers communicated through those channels will drop.


Multi-decadal Climate Variability and the “Warming Hole” in North America

Multi-decadal Climate Variability and the “Warming Hole” in North America – results from CMIP5 20th and 21st Century Climate Simulations – Kumar et al. (2012) [FULL TEXT]

Abstract: “The ability of Coupled Model Intercomparison Project Phase 5 (CMIP5) climate models to simulate the 20th century “warming hole” over North America is explored, along with the warming hole’s relationship with natural climate variability. Twenty first century warming hole projections are also examined for two future emission scenarios, the 8.5 and 4.5 Wm−2 representative concentration pathways (RCP8.5 and RCP4.5). We have analyzed simulations from 22 CMIP5 climate models including all their ensemble members, a total of 192 climate realizations. We have employed a non-parametric trend detection method, and an alternative perspective emphasizing trend variability. Observations show multi-decadal variability in the sign and magnitude of the trend, where the 20th century temperature trend over the eastern United States appears to be associated with low frequency (multi-decadal) variability in the North Atlantic temperatures. Most CMIP5 climate models simulate significantly lower ‘relative power’ in the North Atlantic multi-decadal oscillations than observed. Models that have relatively higher skill in simulating the North-Atlantic multi-decadal oscillation also are more likely to reproduce the warming hole. We also find that the trend variability envelope simulated by multiple CMIP5 climate models brackets the observed warming hole. Based on the multi-model analysis, we find that in the 21st century climate simulations the presence or absence of the warming hole would depend upon the future emission scenarios; the RCP8.5 scenario indicates a disappearance of the warming hole, while the RCP4.5 scenario shows some chance (10-20%) of the warming hole’s reappearance in the latter half of the 21st century consistent with CO2 stabilization.”

Citation: Sanjiv Kumar, James Kinter, Paul A. Dirmeyer, Zaitao Pan, and Jennifer Adams, Journal of Climate 2012, doi: http://dx.doi.org/10.1175/JCLI-D-12-00535.1.


Annual maximum daily precipitation has increased globally

Global increasing trends in annual maximum daily precipitation – Westra et al. (2012)

Abstract: “This study investigates the presence of trends in annual maximum daily precipitation timeseries obtained from a global dataset of 8326 high quality land-based observing stations with more than 30 years of record over the period from 1900 to 2009. Two complementary statistical techniques were adopted to evaluate the possible non-stationary behaviour of this precipitation data. The first was a Mann-Kendall non-parametric trend test, and was used to evaluate the existence of monotonic trends. The second was a non-stationary generalised extreme value analysis, and was used to determine the strength of association between the precipitation extremes and globally averaged near-surface temperature. The outcomes are that statistically significant increasing trends can be detected at the global scale, with close to two-thirds of stations showing increases. Furthermore, there is a statistically significant association with globally averaged near-surface temperature, with the median intensity of extreme precipitation changing in proportion with changes in global mean temperature at a rate of between 5.9% and 7.7% per degree, depending on the method of analysis. This ratio was robust irrespective of record length or time period considered, and was not strongly biased by the uneven global coverage of precipitation data. Finally, there is a distinct meridional variation, with the greatest sensitivity occurring in the tropics and higher latitudes, and minima around 13°S and 11°N. The greatest uncertainty was near the equator due to the limited number of sufficiently long precipitation records, and there remains an urgent need to improve data collection in this region to better constrain future changes in tropical precipitation.”

Citation: Seth Westra, Lisa V. Alexander, and Francis W. Zwiers, Journal of Climate 2012, doi: http://dx.doi.org/10.1175/JCLI-D-12-00502.1.


Human influence shows in extratropical Southern Hemisphere summer precipitation

Human influence on extratropical Southern Hemisphere summer precipitation – Fyfe et al. (2012)

Highlights: •Observed precipitation trends inconsistent with simulated internal variability; •Observed precipitation trends mainly due to anthropogenic and natural forcings; •Specifically from GHG and ozone changes, with opposing influence from aerosols.

Abstract: “Observations of extratropical Southern Hemisphere austral summer precipitation over recent decades show mid-latitude drying and high-latitude moistening. Here we show that the observed precipitation trends in two datasets are inconsistent with simulated internal variability, but are closely consistent with trends simulated in response to historical changes in anthropogenic and natural forcings. Simulations with individual anthropogenic and natural forcings suggest that the observed pattern of precipitation change is substantially forced by anthropogenic greenhouse gas and ozone changes, with an opposing influence from aerosols. Our results demonstrate that human influence had a significant impact on precipitation across the mid and high latitudes of the Southern Hemisphere, changes which are expected to have a profound impact on Southern Ocean stratification and hence on ocean-atmosphere heat and carbon fluxes.”

Citation: Fyfe, J. C., N. P. Gillett, and G. J. Marshall (2012), Human influence on extratropical Southern Hemisphere summer precipitation, Geophys. Res. Lett., 39, L23711, doi:10.1029/2012GL054199.


Quaternary International is publishing a special issue on dendrochronology in Asia

Dendrochronology in Asia – Quaternary International (2013)

Selected quotes from editorial: “In August 2011, the Second International Asian Dendrochronological Conference was held in Xian, China. During five days, over 150 participants from China, India, Thailand, Korea, Nepal, Japan, Pakistan, Iran, Mongolia, and countries outside of Asia gathered, and more than 65 presentations were given. A wide range of the dendrochronological sciences was covered in sessions dedicated to dendroclimatology, dendroecology, dendroarchaeology, dendrohydrology, wood anatomy, and stable isotope applications… …In this special issue of Quaternary International, selected papers presented at the conference have been assembled. These papers provide a nice overview of the current state of Asian dendrochronology, albeit with focus on China.”

Citation: Quaternary International, Volume 283, Pages 1-146 (14 January 2013), edited by Hans Linderholm, Yu Liu, Steven Leavitt and Eryuan Liang.


Deforestation can lead to irreversible state shifts where the forest vegetation cannot recover

Physical and biological feedbacks of deforestation – Runyan et al. (2012)

Highlights: •Forest vegetation can enhance conditions favorable to its own existence; •Removal of forest vegetation can alter conditions necessary to sustain growth; •Deforestation can lead to irreversible state shifts.

Abstract: “Forest vegetation can interact with its surrounding environment in ways that enhance conditions favorable for its own existence. Removal of forest vegetation has been shown to alter these conditions in a number of ways, thereby inhibiting the reestablishment of the same community of woody plants. The effect of vegetation on an environmental variable along with vegetation susceptibility to the associated environmental conditions may imply a positive feedback: Changes in the internal conditions controlling this variable such as deforestation could inhibit the reestablishment of woody vegetation cover that in turn would act to further degrade the conditions necessary for forest regeneration. Understanding these feedbacks is important because in some cases where these feedbacks are present, deforestation can lead to irreversible state shifts where the forest vegetation cannot recover. In this review, we examine the different cases in which deforestation can lead to a loss of conditions necessary to sustain forest vegetation. We examine the spatial scale and extent of each feedback in addition to considering the temporal scale over which a feedback may be considered irreversible. Juxtaposing the spatial extent of these feedbacks with a map of deforestation enables the identification and discussion of at-risk areas to state changes following deforestation. Last, we discuss the economic implications of these feedbacks and how socioeconomic factors can affect the convergence of a system to a given stable state.”

Citation: Runyan, C. W., P. D’Odorico, and D. Lawrence (2012), Physical and biological feedbacks of deforestation, Rev. Geophys., 50, RG4006, doi:10.1029/2012RG000394.


Montreal Protocol has prevented climate change and catastrophic ozone loss

“World avoided” simulations with the Whole Atmosphere Community Climate Model – Garcia et al. (2012)

Highlights: •The Montreal Protocol has prevented climate change and catastrophic ozone loss; •Heterogeneous chemistry hastens ozone collapse but is not needed to produce it; •The collapse of tropical ozone is reversed quickly if ODS emissions cease.

Abstract: “We use the Whole Atmosphere Community Climate Model, coupled to a deep ocean model, to investigate the impact of continued growth of halogenated ozone depleting substances (ODS) in the absence of the Montreal Protocol. We confirm the previously reported result that the growth of ODS leads to a global collapse of the ozone layer in mid-21st century, with column amounts falling to 100 DU or less at all latitudes. We also show that heterogeneous activation of chlorine in the lower stratosphere hastens this collapse but is not essential to produce it. The growth of ODS, which are also greenhouse gases, produces a radiative forcing of 4 W m−2 by 2070, nearly equal that of the non-ODS greenhouse gases CO2, CH4, and N2O in the RCP4.5 scenario of IPCC. This leads to surface warming of over 2 K in the tropics, 6 K in the Arctic, and close to 4 K in Antarctica in 2070 compared to the beginning of the century. We explore the reversibility of these impacts following complete cessation of ODS emissions in the mid-2050s. We find that impacts are reversed on various time scales, depending on the atmospheric lifetime of the ODS that cause them. Thus ozone in the lower stratosphere in the tropics and subtropics recovers very quickly because the ODS that release chlorine and bromine there (e.g., methyl chloroform and methyl bromide) have short atmospheric lifetimes and are removed within a few years. On the other hand, ozone depletion in the polar caps and global radiative forcing depend on longer-lived ODS, such that much of these impacts persist through the end of our simulations  in 2070.”

Citation: Garcia, R. R., D. E. Kinnison, and D. R. Marsh (2012), “World avoided” simulations with the Whole Atmosphere Community Climate Model, J. Geophys. Res., 117, D23303, doi:10.1029/2012JD018430.


New study says Laki eruption contributed to 1783-1784 winter cooling

Climatic impact of the long-lasting 1783 Laki eruption: Inapplicability of mass-independent sulfur isotopic composition measurements – Schmidt et al. (2012)

Highlights: •1783-84 CE Laki eruption produced multiyear impact on NH surface temperatures, •Laki produced stratospheric injection and contributed to 1783-84 winter cooling, •S isotope measurements not applicable for interpreting Laki’s climatic impact.

Abstract: “The long-lasting 1783–1784 CE Laki flood lava eruption in Iceland released around 120 Tg of sulfur dioxide into the upper troposphere/lower stratosphere. Northern Hemisphere temperature proxy records of the 1780s indicate below-average temperatures for up to three years following the eruption. The very warm summer of 1783 in Europe, which was followed by a very cold winter, may have been caused by the eruption, but the mechanisms are not yet well understood. Some studies attributed the cold winter 1783–1784 to natural variability of climate. However, our climate model simulations show that the Laki radiative effects lasted long enough to contribute to the winter cooling. We suggest that sulfur isotopic composition measurements obtained using samples from Greenland ice cores do not provide evidence of either a short-lived volcanic aerosol cloud or a short-lived climatic impact of the Laki eruption. In fact, the applicability of mass-independent sulfur isotopic composition measurements for interpreting the climatic impact of any high-latitude eruption remains yet to be demonstrated.”

Citation: Schmidt, A., T. Thordarson, L. D. Oman, A. Robock, and S. Self (2012), Climatic impact of the long-lasting 1783 Laki eruption: Inapplicability of mass-independent sulfur isotopic composition measurements, J. Geophys. Res., 117, D23116, doi:10.1029/2012JD018414.


It’s all tiny details nowadays: Impact of dust particle non-sphericity on climate simulations

Impact of dust particle non-sphericity on climate simulations – Räisänen et al. (2012)

Abstract: “Although mineral aerosol (dust) particles are irregular in shape, they are treated as homogeneous spheres in climate model radiative transfer calculations. Here, we test the effect of dust particle non-sphericity in the ECHAM5.5-HAM2 global aerosol–climate model. The short-wave optical properties of the two insoluble dust modes in HAM2 are modelled using an ensemble of spheroids that has been optimized to reproduce the optical properties of dust-like aerosols, thereby providing a significant improvement over spheres. First, the direct radiative effects (DRE) of dust non-sphericity were evaluated diagnostically, by comparing spheroids with both volume-equivalent and volume-to-area (V/A) equivalent spheres. In the volume-equivalent case, the short-wave DRE of insoluble dust at the surface and at the top of the atmosphere (TOA) was slightly smaller (typically by 3–4%) for spheroidal than for spherical dust particles. This rather small difference stems from compensating non-sphericity effects on the dust optical thickness and asymmetry parameter. In the V/A-equivalent case, the difference in optical thickness was virtually eliminated and the DRE at the TOA (surface) was ∼20% (∼13%) smaller for spheroids than for spheres, due to a larger asymmetry parameter. Even then, however, the global-mean DRE of non-sphericity was only 0.055 W m−2 at the TOA and 0.070 W m−2 at the surface. Subsequently, the effects of dust non-sphericity were tested interactively in simulations in which ECHAM5.5-HAM2 was coupled to a mixed-layer ocean model. Consistent with the rather small radiative effects noted above, the climatic differences from simulations with spherical dust optics were generally negligible.”

Citation: P. Räisänen, P. Haapanala, C. E. Chung, M. Kahnert, R. Makkonen, J. Tonttila, T. Nousiainen, Quarterly Journal of the Royal Meteorological Society, DOI: 10.1002/qj.2084.


Clouds are important also for Martian climate

The influence of radiatively active water ice clouds on the Martian climate – Madeleine et al. (2012)

Highlights: •Radiatively active clouds (RAC) are implemented in the LMD global climate model; •Whatever the season, including RAC is required to fit the observed temperatures; •Renewed attention on the polar regions, where cold biases remain, is needed.

Abstract: “Radiatively active water ice clouds (RAC) play a key role in shaping the thermal structure of the Martian atmosphere. In this paper, RAC are implemented in the LMD Mars Global Climate Model (GCM) and the simulated temperatures are compared to Thermal Emission Spectrometer observations over a full year. RAC change the temperature gradients and global dynamics of the atmosphere and this change in dynamics in turn implies large-scale adiabatic temperature changes. Therefore, clouds have both a direct and indirect effect on atmospheric temperatures. RAC successfully reduce major GCM temperature biases, especially in the regions of formation of the aphelion cloud belt where a cold bias of more than 10 K is corrected. Departures from the observations are however seen in the polar regions, and highlight the need for better modeling of cloud formation and evolution.”

Citation: Madeleine, J.-B., F. Forget, E. Millour, T. Navarro, and A. Spiga (2012), The influence of radiatively active water ice clouds on the Martian climate, Geophys. Res. Lett., 39, L23202, doi:10.1029/2012GL053564.


On the statistical significance of surface air temperature trends in the Eurasian Arctic region

On the statistical significance of surface air temperature trends in the Eurasian Arctic region – Franzke (2012)

Highlights: •I am using a novel method to test the significance of temperature trends; •In the Eurasian Arctic region only 17 stations show a significant trend; •I find that in Siberia the trend signal has not yet emerged.

Abstract: “This study investigates the statistical significance of the trends of station temperature time series from the European Climate Assessment & Data archive poleward of 60°N. The trends are identified by different methods and their significance is assessed by three different null models of climate noise. All stations show a warming trend but only 17 out of the 109 considered stations have trends which cannot be explained as arising from intrinsic climate fluctuations when tested against any of the three null models. Out of those 17, only one station exhibits a warming trend which is significant against all three null models. The stations with significant warming trends are located mainly in Scandinavia and Iceland.”

Citation: Franzke, C. (2012), On the statistical significance of surface air temperature trends in the Eurasian Arctic region, Geophys. Res. Lett., 39, L23705, doi:10.1029/2012GL054244.


Ozone might have been one factor in Snowball Earth

Radiative effects of ozone on the climate of a Snowball Earth – Yang et al. (2012) [FULL TEXT]

Abstract: “Some geochemical and geological evidence has been interpreted to suggest that the concentration of atmospheric oxygen was only 1–10 % of the present level in the time interval from 750 to 580 million years ago when several nearly global glaciations or Snowball Earth events occurred. This low concentration of oxygen would have been accompanied by a lower ozone concentration than exists at present. Since ozone is a greenhouse gas, this change in ozone concentration would alter surface temperature, and thereby could have an important influence on the climate of the Snowball Earth. Previous works that have focused either on initiation or deglaciation of the proposed Snowball Earth has not taken the radiative effects of ozone changes into account. We address this issue herein by performing a series of simulations using an atmospheric general circulation model with various ozone concentrations. Our simulation results demonstrate that, as ozone concentration is uniformly reduced from 100 % to 50 %, surface temperature decreases by approximately 0.8 K at the Equator, with the largest decreases located in the middle latitudes reaching as high as 2.5 K. When ozone concentration is reduced and its vertical and horizontal distribution is simultaneously modulated, surface temperature decreases by 0.4–1.0 K at the Equator and by 4–7 K in polar regions. These results here have uncertainties, depending on model parameterizations of cloud, surface snow albedo, and relevant feedback processes, while they are qualitatively consistent with radiative-convective model results that do not involve such parameterizations and feedbacks. These results suggest that ozone variations could have had a moderate impact on the climate during the Neoproterozoic glaciations.”

Citation: Yang, J., Hu, Y., and Peltier, W. R.: Radiative effects of ozone on the climate of a Snowball Earth, Clim. Past, 8, 2019-2029, doi:10.5194/cp-8-2019-2012, 2012.


In future there will be climates unlike the present ones in some Earth zones

Modelling future no-analogue climate distributions: A world-wide phytoclimatic niche-based survey – García-López & Allué (2012)

Highlights: ► The percentage of the world surface that will foreseeably be occupied by no-analogue climates by 2080 ranges between 3.5% and 17.5% ► We present a numerical and cartographic evaluation of these no-analogue climatic zones ► The bulk of the no-analogue surface area will foreseeably be located in the Northern hemisphere (> 80%), more probably in tropical and subtropical latitudes between 10 degrees latitude South and 30 degrees latitude North. ► 32 of the 34 hotspots defined for the planet, especially tropical forests in South America and Asia will be affected by no-analog conditions. 6.8% of these conservation-critical surfaces are predicted as no-analogue areas ► Population density is greater in the areas that will probably develop no-analogue climates in the future than in those that will not.

Abstract: “By the end of the 21st century in some zones the accelerating climate change affecting this planet will create factorial combinations unknown at this time, which will give rise to climates unlike the present ones. This study presents a numerical and cartographic evaluation of these no-analogue climatic zones, whose consequences for existing ecosystems are quite unpredictable, using a method based on the convex hull in a climate hyperspace and 12 future climate projections for 2080. The percentage of the world surface that will foreseeably be occupied by no-analogue climates by 2080 ranges between 3.5% and 17.5%. The bulk of the no-analogue surface area will foreseeably be located in the Northern hemisphere (> 80%), with more elevated risk in tropical and subtropical latitudes between 10 degrees latitude South and 30 degrees latitude North, preferentially in Africa, South America, the Arabian Peninsula, the Indian Peninsula, the North-West of the Gulf of Mexico, Eastern China and Polynesia. Mean temperatures would appear to be the variables most influencing the process. This affects 32 of the 34 hotspots defined for the planet, especially tropical forests in South America and Asia. 6.8% of these conservation-critical surfaces are predicted as no-analogue areas. Population density is greater in the areas that will probably develop no-analogue climates in the future than in those that will not.”

Citation: Javier M. García-López, Carmen Allué, Global and Planetary Change, http://dx.doi.org/10.1016/j.gloplacha.2012.12.001.


Other studies from last week

Global climate change in large European rivers: long-term effects on macroinvertebrate communities and potential local confounding factors – Floury et al. (2012)

Impacts of Atmospheric Temperature Trends on Tropical Cyclone Activity – Vecchi et al. (2012)

The Influence of Atlantic Tropical Cyclones on Drought over the Eastern US (1980-2007) – Kam et al. (2012)

Faint young Sun problem more severe due to ice-albedo feedback and higher rotation rate of the early Earth – Kienert et al. (2012)

The great Arctic cyclone of August 2012 – Simmonds & Rudeva (2012)

Climate change impacts on Central Asian water resources – Malsy et al. (2012) [FULL TEXT]

Carbon emissions from land use and land-cover change – Houghton et al. (2012) [FULL TEXT]

On the Measurement of Heatwaves – Perkins & Alexander (2012)

A near real-time satellite-based global drought climate data record – AghaKouchak & Nakhjiri (2012) [FULL TEXT]

The role of upper-level dynamics and surface processes for the Pakistan flood of July 2010 – Martius et al. (2012)

Recent tropospheric ozone changes – A pattern dominated by slow or no growth – Oltmans et al. (2012)

Brief communication “Stratospheric winds, transport barriers and the 2011 Arctic ozone hole” – Olascoaga et al. (2012)

The impact of greenhouse gases on past changes in tropospheric ozone – Lang et al. (2012)

Quantifying the seasonal “breathing” of the Antarctic ice sheet – Ligtenberg et al. (2012)

The effect of snow cover on lemming population cycles in the Canadian High Arctic – Bilodeau et al. (2012)

A 20 year independent record of sea surface temperature for climate from Along-Track Scanning Radiometers – Merchant et al. (2012)

Assessment of regional climate model simulation estimates over the northeast United States – Rawlins et al. (2012)

Radiation budget changes with dry forest clearing in temperate Argentina – Houspanossian et al. (2012)

Adaptation to climate change through the choice of cropping system and sowing date in sub-Saharan Africa – Waha et al. (2012)

Global burned area and biomass burning emissions from small fires – Randerson et al. (2012)


CLASSIC OF THE WEEK: Stoney (1898)

Of Atmospheres upon Planets and Satellites – Stoney (1898) [FULL TEXT]

Abstract: No abstract.

Citation: Stoney, G. Johnstone, Astrophysical Journal, vol. 7, p.25, DOI: 10.1086/140435.


About this series. When each paper is published, it is notified in AGW Observer Facebook page and Twitter page. Here’s the archive for the research papers of previous weeks. If this sort of thing interests you, be sure to check out A Few Things Illconsidered. They also have a weekly posting containing lots of links to new research and other climate related news.

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