AGW Observer

Observations of anthropogenic global warming

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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