AGW Observer

Observations of anthropogenic global warming

New research from last week 32/2011

Posted by Ari Jokimäki on August 15, 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 the atmospheric circulation over tropical Pacific

A Shift in Western Tropical Pacific Sea Level Trends during the 1990s – Merrifield (2011) “Pacific Ocean sea surface height trends from satellite altimeter observations for 1993–2009 are examined in the context of longer tide gauge records and wind stress patterns. The dominant regional trends are high rates in the western tropical Pacific and minimal to negative rates in the eastern Pacific, particularly off North America. Interannual sea level variations associated with El Niño–Southern Oscillation events do not account for these trends. In the western tropical Pacific, tide gauge records indicate that the recent high rates represent a significant trend increase in the early 1990s relative to the preceding 40 years. This sea level trend shift in the western Pacific corresponds to an intensification of the easterly trade winds across the tropical Pacific. The wind change appears to be distinct from climate variations centered in the North Pacific, such as the Pacific decadal oscillation. In the eastern Pacific, tide gauge records exhibit higher-amplitude decadal fluctuations than in the western tropical Pacific, and the recent negative sea level trends are indistinguishable from these fluctuations. The shifts in trade wind strength and western Pacific sea level rate resemble changes in dominant global modes of outgoing longwave radiation and sea surface temperature. It is speculated that the western Pacific sea level response indicates a general strengthening of the atmospheric circulation over the tropical Pacific since the early 1990s that has developed in concert with recent warming trends.” Merrifield, Mark A., 2011: A Shift in Western Tropical Pacific Sea Level Trends during the 1990s. J. Climate, 24, 4126–4138, doi: 10.1175/2011JCLI3932.1. [Full text]

Antarctic waters are warming

Multi-decadal warming and shoaling of Antarctic Intermediate Water – Schmidtko & Johnson (2011) “Antarctic Intermediate Water (AAIW) is a dominant Southern Hemisphere water mass that spreads from its formation regions just north of the Antarctic Circumpolar Current (ACC) to at least 20°S in all oceans. This study uses an isopycnal climatology constructed from Argo Conductivity-Temperature-Depth (CTD) profile data to define the current state of the AAIW salinity minimum (its core) and thence compute AAIW core pressure, potential temperature, salinity, and potential density anomalies since the mid-1970s from ship-based CTD profiles. The results are used to calculate maps of temporal property trends at the AAIW core, where statistically significant strong circumpolar shoaling (30–50 dbar decade−1), warming (0.05–0.15°C decade−1), and density reductions (up to −0.03 kg m−3 decade−1) are found. These trends are strongest just north of the ACC in the southeast Pacific and Atlantic oceans and decrease equatorward. Salinity trends are generally small, with their sign varying regionally. Bottle data are used to extend the AAIW core potential temperature anomaly analysis back to 1925 in the Atlantic, and ~1960 elsewhere. The modern warm AAIW core conditions appear largely unprecedented in the historical record: biennially and zonally binned median AAIW core potential temperatures within each ocean basin are, with the notable exception of the subtropical South Atlantic in the 1950s–70s, 0.2–1°C colder than modern values. Zonally averaged sea surface temperature anomalies around the AAIW formation latitudes in each ocean and sectoral Southern Annular Mode indices are used to put the AAIW core property trends and variations into context.” Sunke Schmidtko and Gregory C. Johnson, Journal of Climate 2011, doi: 10.1175/JCLI-D-11-00021.1. [Full text]

Analysis of snow cover changes in the Himalayan region

An analysis of snow cover changes in the Himalayan region using MODIS snow products and in-situ temperature data – Maskey et al. (2011) “Amidst growing concerns over the melting of the Himalayas’ snow and glaciers, we strive to answer some of the questions related to snow cover changes in the Himalayan region covering Nepal and its vicinity using Moderate Resolution Imaging Spectroradiometer (MODIS) snow cover products from 2000 to 2008 as well as in-situ temperature data from two high altitude stations and net radiation and wind speed data from one station. The analysis consists of trend analysis based on the Spearman’s rank correlation on monthly, seasonal and annual snow cover changes over five different elevation zones above 3,000 m. There are decreasing trends in January and in winter for three of the five elevation zones (all below 6,000 m), increasing trends in March for two elevation zones above 5,000 m and increasing trends in autumn for four of the five elevation zones (all above 4,000 m). Some of these observed trends, if continue, may result in changes in the spring and autumn season river flows in the region. Dominantly negative correlations are observed between the monthly snow cover and the in-situ temperature, net radiation and wind speed from the Pyramid station at 5,035 m (near Mount Everest). Similar correlations are also observed between the snow cover and the in-situ temperature from the Langtang station at 3,920 m elevation. These correlations explain some of the observed trends and substantiate the reliability of the MODIS snow cover products.” Shreedhar Maskey, Stefan Uhlenbrook and Sunal Ojha, Climatic Change, DOI: 10.1007/s10584-011-0181-y.

Borehole measurements show increasing temperatures in East Antarctica

Recent surface temperature trends in the interior of East Antarctica from borehole firn temperature measurements and geophysical inverse methods – Muto et al. (2011) “We use measured firn temperatures down to depths of 80 to 90 m at four locations in the interior of Dronning Maud Land, East Antarctica to derive surface temperature histories spanning the past few decades using two different inverse methods. We find that the mean surface temperatures near the ice divide (the highest-elevation ridge of East Antarctic Ice Sheet) have increased approximately 1 to 1.5 K within the past ∼50 years, although the onset and rate of this warming vary by site. Histories at two locations, NUS07-5 (78.65°S, 35.64°E) and NUS07-7 (82.07°S, 54.89°E), suggest that the majority of this warming took place in the past one or two decades. Slight cooling to no change was indicated at one location, NUS08-5 (82.63°S, 17.87°E), off the divide near the Recovery Lakes region. In the most recent decade, inversion results indicate both cooler and warmer periods at different sites due to high interannual variability and relatively high resolution of the inverted surface temperature histories. The overall results of our analysis fit a pattern of recent climate trends emerging from several sources of the Antarctic temperature reconstructions: there is a contrast in surface temperature trends possibly related to altitude in this part of East Antarctica.” Muto, A., T. A. Scambos, K. Steffen, A. G. Slater, and G. D. Clow (2011), Geophys. Res. Lett., 38, L15502, doi:10.1029/2011GL048086.

What happens to boreal soils under climate change?

Boreal and subarctic soils under climatic change – Helama et al. (2011) “Changing climate and warming atmosphere are supposed to result in changing thermal regimes of soils with a spectrum of impacts for terrestrial heat-flow, ecological and biochemical processes including vegetation and carbon dynamics. Here, six sites within an area of significant recent climatic warming, between 70° and 60°N, provided data of air and soil temperatures and snow depth to analyze the spatiotemporal air-soil temperature associations during the period 1971–2010. The air temperatures exhibited significant trends of warming across the boreal and subarctic region. The records of snow depth showed trends of snowpack thinning and the soil temperatures trends of warming especially in the southern and middle boreal sites. The boreal and subarctic sites showed predominant influence of air temperature variability on soil thermal conditions, with modulating effects of thermoinsulation caused by the snowpack. The yearly variations in soil temperatures correlated highly with those of air temperatures and the positive trend in soil temperatures was sufficiently explained by air temperature warming in the majority of the sites. The results thus propose that the climate change could be directly causing alterations in the soil thermal regime and the warming of soils, with generally expected continuation, driven by air temperature warming as projected by model simulations. The thermoinsulation effects during the winter were strongest in the northern boreal zone where the temperature difference between the air and soil temperatures was largest and the correlations between snow depth and soil temperatures were highest during the winter months. Likewise, the rate of air temperature warming appeared strongest in our northern boreal site where the soil temperature warming showed non-significant trend only. The evidence for temporal air-soil temperature decouplings and spatial disparity between the air and soil temperature data both expressed the importance of studying the soil temperature change in situ. In the same context, the potential for temperature induced soil organic carbon decomposition coincided spatially with the highest quantities of available carbon as indicated for our boreal and subarctic soils.” Samuli Helama, Heikki Tuomenvirta and Ari Venäläinen, Global and Planetary Change, doi:10.1016/j.gloplacha.2011.08.001.

In snowy regions snow explains most of winter surface temperature variability

Land-atmosphere coupling associated with snow cover – Dutra et al. (2011) “This study investigates the role of interannual snow cover variability in controlling the land-atmosphere coupling and its relation with near surface (T2M) and soil temperature (STL1). Global atmospheric simulations are carried out with the EC-EARTH climate model using climatological sea surface temperature and sea ice distributions. Snow climatology, derived from a control run (COUP), is used to replace snow evolution in the snow-uncoupled simulation (UNCOUP). The snow cover and depth variability explains almost 60% of the winter T2M variability in predominantly snow-covered regions. During spring the differences in interannual variability of T2M are more restricted to the snow line regions. The variability of soil temperature is also damped in UNCOUP. However, there are regions with a pronounced signal in STL1 with no counterpart in T2M. These regions are characterized by a significant interannual variability in snow depth, rather than snow cover (almost fully snow covered during winter). These results highlight the importance of both snow cover and snow depth in decoupling the soil temperature evolution from the overlying atmosphere.” Dutra, E., C. Schär, P. Viterbo, and P. M. A. Miranda (2011), Geophys. Res. Lett., 38, L15707, doi:10.1029/2011GL048435.

Large decadal decline of the Arctic multiyear ice

Large Decadal Decline of the Arctic Multiyear Ice Cover – Comiso (2011) “The perennial ice area was drastically reduced to 38% of its climatological average in 2007 but recovered slightly in 2008, 2009 and 2010 with the areas being 10%, 24%, and 11% higher than in 2007, respectively. However, trends in extent and area remained strongly negative at −12.2% and −13.5 %/decade, respectively. The thick component of the perennial ice, called multiyear ice, as detected by satellite data in the winters of 1979 to 2011 was studied and results reveal that the multiyear ice extent and area are declining at an even more rapid rate of −15.1% and −17.2 % per decade, respectively, with record low value in 2008 followed by higher values in 2009, 2010 and 2011. Such high rate in the decline of the thick component of the Arctic ice cover means a reduction in average ice thickness and an even more vulnerable perennial ice cover. The decline of the multiyear ice area from 2007 to 2008 was not as strong as that of the perennial ice area from 2006 to 2007 suggesting a strong role of second year ice melt in the latter. The sea ice cover is shown to be strongly correlated with surface temperature which is increasing at about three times global average in the Arctic but appears weakly correlated with the AO which controls the atmospheric circulation in the region. An 8 to 9-year cycle is apparent in the multiyear ice record which could explain in part the slight recovery in the last three years.” Josefino C. Comiso, Journal of Climate 2011, doi: 10.1175/JCLI-D-11-00113.1.

Analysis of fast draining lakes on the Greenland Ice Sheet

Fast draining lakes on the Greenland Ice Sheet – Selmes et al. (2011) “The rapid drainage of supraglacial lakes around the ablation zone of the Greenland Ice Sheet forms an important link between water at the surface and the ice sheet base, allowing surface meltwater to reach the bed and hence increase glacial velocity. The conduits formed by lake drainages may remain open during the remainder of the melt season providing a pathway for further meltwater to reach the base. We investigated the drainage behavior of lakes from all regions of the Greenland Ice Sheet for the period 2005–2009. We mapped the evolution of 2600 lakes from 3704 MODIS images detecting a mean of 263 drainage events per year, of which 61% occurred in the south-west region. Only 1% of lake drainages occurred in the rapidly thinning south-east region. Our results show marked differences between the hydrology of the different regions of the ice sheet, with few lake drainages occurring in the regions where the highest dynamic mass loss is occurring. In the south-west and north-east, lake drainages are common and could impact glacier dynamics; in the south-east they are rare and are thus unlikely to do so.” Selmes, N., T. Murray, and T. D. James (2011), Geophys. Res. Lett., 38, L15501, doi:10.1029/2011GL047872.

CO2 levels might not have been very high during Early Cretaceous

Early Cretaceous atmospheric pCO2 level recorded from pedogenic carbonates in China – Huang et al. (2011) “Pedogenic carbonates were collected from Early Cretaceous strata in Sichuan and Liaoning, China. These paleosol carbonates and calcareous paleosols were evaluated in order to reconstruct atmospheric CO2 concentrations during the Early Cretaceous using a paleosol barometer. Using the isotopic ratios of pedogenic carbonates from Early Cretaceous (early-middle Berriasian, early Valanginian) strata in Sichuan Basin, averaged atmospheric pCO2 is estimated to have been 360 ppmv in the early-middle Berriasian and a mean value of 241 ppmv in the early Valanginian. In the late Barremian in western Liaoning, however the average was 530 ppmv, with a range of 365 ppmv and 644 ppmv, lower than previous estimates of pCO2 for these time periods, consistent with the suggestion of overall climate cooling and paleotemperature fluctuation during the Early Cretaceous. This indicates that not all of the Cretaceous was a high or continuous CO2 greenhouse, especially during Early Cretaceous.” C.M. Huang, G.J. Retallack and C.S. Wang, Cretaceous Research, doi:10.1016/j.cretres.2011.08.001.

Cosmic ray contribution to global warming less than 8% since 1900

The contribution of cosmic rays to global warming – Sloan & Wolfendale (2011) “A search has been made for a contribution of the changing cosmic ray intensity to the global warming observed in the last century. The cosmic ray intensity shows a strong 11 year cycle due to solar modulation and the overall rate has decreased since 1900. These changes in cosmic ray intensity are compared to those of the mean global surface temperature to attempt to quantify any link between the two. It is shown that, if such a link exists, the changing cosmic ray intensity contributes less than 8% to the increase in the mean global surface temperature observed since 1900.” T. Sloan and A.W. Wolfendale, Journal of Atmospheric and Solar-Terrestrial Physics, doi:10.1016/j.jastp.2011.07.013. [Full text]

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