AGW Observer

Observations of anthropogenic global warming

New research from last week 14/2011

Posted by Ari Jokimäki on April 11, 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:

Positive climate feedback from boreal tundra expansion

Late Pliocene to Pleistocene sensitivity of the Greenland Ice Sheet in response to external forcing and internal feedbacks – Koenig et al. (2011) “The timing and nature of ice sheet variations on Greenland over the last ∼5 million years remain largely uncertain. Here, we use a coupled climate-vegetation-ice sheet model to determine the climatic sensitivity of Greenland to combined sets of external forcings and internal feedbacks operating on glacial-interglacial timescales. In particular, we assess the role of atmospheric pCO2, orbital forcing, and vegetation dynamics in modifying thresholds for the onset of glaciation in late Pliocene and Pleistocene. The response of circum-Arctic vegetation to declining levels of pCO2 (from 400 to 200 ppmv) and decreasing summer insolation includes a shift from boreal forest to tundra biomes, with implications for the surface energy balance. The expansion of tundra amplifies summer surface cooling and heat loss from the ground, leading to an expanded summer snow cover over Greenland. Atmospheric and land surface fields respond to forcing most prominently in late spring-summer and are more sensitive at lower Pleistocene-like levels of pCO2. We find cold boreal summer orbits produce favorable conditions for ice sheet growth, however simulated ice sheet extents are highly dependent on both background pCO2 levels and land-surface characteristics. As a result, late Pliocene ice sheet configurations on Greenland differ considerably from late Pleistocene, with smaller ice caps on high elevations of southern and eastern Greenland, even when orbital forcing is favorable for ice sheet growth.” Sebastian J. Koenig, Robert M. DeConto and David Pollard, Climate Dynamics, DOI: 10.1007/s00382-011-1050-0.

Positive climate feedback from boreal forest expansion

The effects of boreal forest expansion on the summer Arctic frontal zone – Liess et al. (2011) “Over the last 100 years, Arctic warming has resulted in a longer growing season in boreal and tundra ecosystems. This has contributed to a slow northward expansion of the boreal forest and a decrease in the surface albedo. Corresponding changes to the surface and atmospheric energy budgets have contributed to a broad region of warming over areas of boreal forest expansion. In addition, mesoscale and synoptic scale patterns have changed as a result of the excess energy at and near the surface. Previous studies have identified a relationship between the positioning of the boreal forest-tundra ecotone and the Arctic frontal zone in summer. This study examines the climate response to hypothetical boreal forest expansion and its influence on the summer Arctic frontal zone. Using the Weather Research and Forecasting model over the Northern Hemisphere, an experiment was performed to evaluate the atmospheric response to expansion of evergreen and deciduous boreal needleleaf forests into open shrubland along the northern boundary of the existing forest. Results show that the lower surface albedo with forest expansion leads to a local increase in net radiation and an average hemispheric warming of 0.6°C at and near the surface during June with some locations warming by 1–2°C. This warming contributes to changes in the meridional temperature gradient that enhances the Arctic frontal zone and strengthens the summertime jet. This experiment suggests that continued Northern Hemisphere high-latitude warming and boreal forest expansion might contribute to additional climate changes during the summer.” Stefan Liess, Peter K. Snyder and Keith J. Harding, Climate Dynamics, DOI: 10.1007/s00382-011-1064-7.

Synthesis of research on Arctic amplification

Processes and Impacts of Arctic Amplification: A Research Synthesis – Serreze & Barry (2011) “The past decade has seen substantial advances in understanding Arctic amplification – that trends and variability in surface air temperature tend to be larger in the Arctic region than for the Northern Hemisphere or globe as a whole. We provide a synthesis of research on Arctic amplification, starting with a historical context and then addressing recent insights into processes and key impacts, based on analysis of the instrumental record, modeling studies, and paleoclimate reconstructions. Arctic amplification is now recognized as an inherent characteristic of the global climate system, with multiple intertwined causes operating on a spectrum of spatial and temporal scales. These include, but are not limited to, changes in sea ice extent that impact heat fluxes between the ocean and the atmosphere, atmospheric and oceanic heat transports, cloud cover and water vapor that alter the longwave radiation flux to the surface, soot on snow and heightened black carbon aerosol concentrations. Strong warming over the Arctic Ocean during the past decade in autumn and winter, clearly associated with reduced sea ice extent, is but the most recent manifestation of the phenomenon. Indeed, periods of Arctic amplification are evident from analysis of both warm and cool periods over at least the past three million years. Arctic amplification being observed today is expected to become stronger in coming decades, invoking changes in atmospheric circulation, vegetation and the carbon cycle, with impacts both within and beyond the Arctic.” Mark C. Serreze and Roger G. Barry, Global and Planetary Change, doi:10.1016/j.gloplacha.2011.03.004.

Mediterranean warming most likely has anthropogenic origin

Consistency of observed near surface temperature trends with climate change projections over the Mediterranean region – Barkhordarian et al. (2011) “We examine the possibility that anthropogenic forcing (Greenhouse gases and Sulfate aerosols, GS) is a plausible explanation for the observed near-surface temperature trends over the Mediterranean area. For this purpose, we compare annual and seasonal observed trends in near-surface temperature over the period from 1980 to 2009 with the response to GS forcing estimated from 23 models derived from CMIP3 database. We find that there is less than a 5% chance that natural (internal) variability is responsible for the observed annual and seasonal area-mean warming except in winter. Using additionally two pattern similarity statistics, pattern correlation and regression, we find that the large-scale component (spatial-mean) of the GS signal is detectable (at 2.5% level) in all seasons except in winter. In contrast, we fail to detect the small-scale component (spatial anomalies about the mean) of GS signal in observed trend patterns. Further, we find that the recent trends are significantly (at 2.5% level) consistent with all the 23 GS patterns, except in summer and spring, when 9 and 5 models respectively underestimate the observed warming. Thus, we conclude that GS forcing is a plausible explanation for the observed warming in the Mediterranean region. Consistency of observed trends with climate change projections indicates that present trends may be understood of what will come more so in the future, allowing for a better communication of the societal challenges to meet in the future.” Armineh Barkhordarian, Jonas Bhend and Hans von Storch, Climate Dynamics, DOI: 10.1007/s00382-011-1060-y. [Full text]

Global sea ice retreats fastest in winter

Consistent changes in the sea ice seasonal cycle in response to global warming – Eisenman et al. (2011) “The Northern Hemisphere sea ice cover has diminished rapidly in recent years and is projected to continue to diminish in the future. The year-to-year retreat of Northern Hemisphere sea ice extent is faster in summer than winter, which has been identified as one of the most striking features of satellite observations as well as of state-of-the-art climate model projections. This is typically understood to imply that the sea ice cover is most sensitive to climate forcing in summertime, and previous studies have explained this by calling on factors such as the surface albedo feedback. However, in the Southern Hemisphere it is the wintertime sea ice extent that retreats fastest in climate model projections. Here, we show that the inter-hemispheric differences in the model projections can be attributed to differences in coastline geometry, which constrain where sea ice can occur. After accounting for coastline geometry, we find that the sea ice changes simulated in both hemispheres in most climate models are consistent with sea ice retreat being fastest in winter in the absence of landmasses. These results demonstrate that despite the widely differing rates of ice retreat among climate model projections, the seasonal structure of the sea ice retreat is robust among the models and uniform in both hemispheres.” Ian Eisenman, Tapio Schneider, David S. Battisti and Cecilia M. Bitz, Journal of Climate 2011, doi: 10.1175/2011JCLI4051.1.

They get wine earlier each year in Australia

Observed trends in winegrape maturity in Australia – Webb et al. (2011) “An extensive assessment of historical trends in winegrape maturity dates from vineyards located in geographically diverse winegrape growing regions in Australia has been undertaken. Records from 44 vineyard blocks, representing a range of varieties of Vitis vinifera L., were accessed. These comprise 33 short-term datasets (average 17 years in length) and 11 long-term datasets, ranging from 25 to 115 years in length (average 50 years). Time series of the day of the year grapes attain maturity were assessed. A trend to earlier maturity of winegrapes was observed in 43 of the 44 vineyard blocks. This trend was significant for six out of the 11 long-term blocks for the complete time period for which records were available. For the period 1993–2009, 35 of the 44 vineyard blocks assessed displayed a statistically significant trend to earlier maturity. The average advance in the phenology was dependent on the time period of observation, with a more rapid advance over more recent decades. Over the more recent 1993–2009 period the average advance was 1.7 days per year, whereas for the period 1985–2009 the rate of advance was 0.8 days per year on average in the 10 long-term vineyard blocks assessed for cross regional comparison. The trend to earlier maturity was associated with warming temperature trends for all of the blocks assessed in the study.” L. B. Webb, P. H. Whetton, E. W. R. Barlow, Global Change Biology, DOI: 10.1111/j.1365-2486.2011.02434.x.

Warming ocean reduces fish swimming ability

Increasing ocean temperature reduces the metabolic performance and swimming ability of coral reef damselfishes – Johansen & Jones (2011) “Tropical coral reef teleosts are exclusively ectotherms and their capacity for physical and physiological performance is therefore directly influenced by ambient temperature. This study examined the effect of increased water temperature to 3°C above ambient on the swimming and metabolic performance of 10 species of damselfishes (Pomacentridae) representing evolutionary lineages from 2 sub-families and 4 genera. Five distinct performance measures were tested: a) maximum swimming speed (Ucrit), b) gait-transition speed (the speed at which they change from strictly pectoral to pectoral-and-caudal swimming, Up−c), c) maximum aerobic metabolic rate (MO2−MAX), d) resting metabolic rate (MO2−REST), and e) aerobic scope (ratio of MO2−MAX to MO2−REST, ASC). Relative to the control (29°C), increased temperature (32°C) had a significant negative effect across all performance measures examined, with the magnitude of the effect varying greatly among closely related species and genera. Specifically, 5 species spanning three genera (Dascyllus, Neopomacentrus and Pomacentrus) showed severe reductions in swimming performance with Ucrit reduced in these species by 21.3–27.9% and Up−c by 32.6–51.3%. Furthermore, 5 species spanning all 4 genera showed significant reductions in metabolic performance with aerobic scope reduced by 24.3–64.9%. Comparisons of remaining performance capacities with field conditions indicate that 32°C water temperatures will leave multiple species with less swimming capacity than required to overcome the water flows commonly found in their respective coral reef habitats. Consequently, unless adaptation is possible, significant loss of species may occur if ocean warming of ≥3°C arises.” J. L. Johansen, G. P. Jones, Global Change Biology, DOI: 10.1111/j.1365-2486.2011.02436.x.

Yet another study showing accelerating Greenland mass loss

Greenland ice sheet mass balance: distribution of increased mass loss with climate warming; 2003-07 versus 1992-2002 – Zwally et al. (2011) “We derive mass changes of the Greenland ice sheet (GIS) for 2003-07 from ICESat laser altimetry and compare them with results for 1992-2002 from ERS radar and airborne laser altimetry. The GIS continued to grow inland and thin at the margins during 2003-07, but surface melting and accelerated flow significantly increased the marginal thinning compared with the 1990s. The net balance changed from a small loss of 7 ± 3 Gt a-1 in the 1990s to 171 ± 4 Gt a-1 for 2003-07, contributing 0.5 mm a-1 to recent global sea-level rise. We divide the derived mass changes into two components: (1) from changes in melting and ice dynamics and (2) from changes in precipitation and accumulation rate. We use our firn compaction model to calculate the elevation changes driven by changes in both temperature and accumulation rate and to calculate the appropriate density to convert the accumulation-driven changes to mass changes. Increased losses from melting and ice dynamics (17-206 Gt a-1) are over seven times larger than increased gains from precipitation (10-35 Gt a-1) during a warming period of ∼2 K (10 a)-1 over the GIS. Above 2000 m elevation, the rate of gain decreased from 44 to 28 Gt a-1, while below 2000 m the rate of loss increased from 51 to 198 Gt a-1. Enhanced thinning below the equilibrium line on outlet glaciers indicates that increased melting has a significant impact on outlet glaciers, as well as accelerating ice flow. Increased thinning at higher elevations appears to be induced by dynamic coupling to thinning at the margins on decadal timescales.” Zwally, H. Jay; Jun, L.I.; Brenner, Anita C.; Beckley, Matthew; Cornejo, Helen G.; Dimarzio, John; Giovinetto, Mario B.; Neumann, Thomas A.; Robbins, John; Saba, Jack L.; Donghui, Y.I.; Wang, Weili, Journal of Glaciology, Volume 57, Number 201, March 2011 , pp. 88-102(15).

Vegetation feedback’s minor influence to global temperature

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.

Evidence against cosmic ray driven ozone depletion

Do cosmic-ray-driven electron-induced reactions impact stratospheric ozone depletion and global climate change? – Grooss & Muller (2011) “Recently, the cosmic-ray-driven electron-induced reaction mechanism (CRE) was introduced to explain polar ozone depletion and surface temperature change. It was proposed that the dissociation of chlorofluorocarbons (CFCs) on ice surfaces of polar stratospheric clouds plays the dominant role in forming the ozone hole. Efforts have been made to predict polar ozone loss into future years. It was further proposed that CFCs and cosmic-ray driven ozone depletion may control global surface temperatures. These assertions challenge the fundamental understanding of Antarctic stratospheric ozone loss and global warming. Here we show that these arguments based on the CRE mechanism are inconclusive. First, correlations of satellite data of CFC-12, N2O and CH4 from ACE-FTS show no evidence of significant loss of CFC- 12 as predicted by the CRE mechanism. Second, conclusions drawn about a possible CRE impact on the atmosphere, based on correlations of different observed atmospheric parameters do not have a physical basis. Finally, predictions on the future development of the atmosphere based on these correlations for both the ozone hole or global surface temperatures are not reliable” Jens-Uwe Grooss and Muller Rolf, Atmospheric Environment, doi:10.1016/j.atmosenv.2011.03.059.

Lake levels rise in Tibet due to glacier melt

Monitoring lake level changes on the Tibetan Plateau using ICESat altimetry data (2003–2009) – Zhang et al. (2011) “In this study, ICESat altimetry data are used to provide precise lake elevations of the Tibetan Plateau (TP) during the period of 2003–2009. Among the 261 lakes examined ICESat data are available on 111 lakes: 74 lakes with ICESat footprints for 4–7 years and 37 lakes with footprints for 1–3 years. This is the first time that precise lake elevation data are provided for the 111 lakes. Those ICESat elevation data can be used as baselines for future changes in lake levels as well as for changes during the 2003–2009 period. It is found that in the 74 lakes (56 salt lakes) examined, 62 (i.e. 84%) of all lakes and 50 (i.e. 89%) of the salt lakes show tendency of lake level increase. The mean lake water level increase rate is 0.23 m/year for the 56 salt lakes and 0.27 m/year for the 50 salt lakes of water level increase. The largest lake level increase rate (0.80 m/year) found in this study is the lake Cedo Caka. The 74 lakes are grouped into four subareas based on geographical locations and change tendencies in lake levels. Three of the four subareas show increased lake levels. The mean lake level change rates for subareas I, II, III, IV, and the entire TP are 0.12, 0.26, 0.19, −0.11, and 0.2 m/year, respectively. These recent increases in lake level, particularly for a high percentage of salt lakes, supports accelerated glacier melting due to global warming as the most likely cause.” Guoqing Zhang, Hongjie Xie, Shichang Kang, Donghui Yi and Stephen F. Ackley, Remote Sensing of Environment, doi:10.1016/j.rse.2011.03.005.

It’s still not the sun

The Smithsonian solar constant data revisited: no evidence for a strong effect of solar activity in ground-based insolation data – Feulner (2011) “Apparent evidence for a strong signature of solar activity in ground-based insolation data was recently reported. In particular, a strong increase of the irradiance of the direct solar beam with sunspot number as well as a decline of the brightness of the solar aureole and the measured precipitable water content of the atmosphere with solar activity were presented. The latter effect was interpreted as evidence for cosmic-ray-induced aerosol formation. Here I show that these spurious results are due to a failure to correct for seasonal variations and the effects of volcanic eruptions and local pollution in the data. After correcting for these biases, neither the atmospheric water content nor the brightness of the solar aureole show any significant change with solar activity, and the variations of the solar-beam irradiance with sunspot number are in agreement with previous estimates. Hence there is no evidence for the influence of solar activity on the climate being stronger than currently thought.” Feulner, G., Atmos. Chem. Phys., 11, 3291-3301, doi:10.5194/acp-11-3291-2011, 2011. [Full text]


One Response to “New research from last week 14/2011”

  1. Ari Jokimäki said

    Fixed the title to 14/2011 instead of 13/2011.

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