AGW Observer

Observations of anthropogenic global warming

New research from last week 34/2011

Posted by Ari Jokimäki on August 29, 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.

Published last week:

Antarctic sea ice trends are due to many factors

A multivariate analysis of Antarctic sea ice since 1979 – Neto et al. (2011) “Recent satellite observations have shown an increase in the total extent of Antarctic sea ice, during periods when the atmosphere and oceans tend to be warmer surrounding a significant part of the continent. Despite an increase in total sea ice, regional analyses depict negative trends in the Bellingshausen-Amundsen Sea and positive trends in the Ross Sea. Although several climate parameters are believed to drive the formation of Antarctic sea ice and the local atmosphere, a descriptive mechanism that could trigger such differences in trends are still unknown. In this study we employed a multivariate analysis in order to identify the response of the Antarctic sea ice with respect to commonly utilized climate forcings/parameters, as follows: (1) The global air surface temperature, (2) The global sea surface temperature, (3) The atmospheric CO2 concentration, (4) The South Annular Mode, (5) The Niño 3, (6) The Niño 3 + 4, 7) The Niño 4, (8) The Southern Oscillation Index, (9) The Multivariate ENSO Index, (10) the Total Solar Irradiance, (11) The maximum O3 depletion area, and (12) The minimum O3 concentration over Antarctica. Our results indicate that western Antarctic sea ice is simultaneously impacted by several parameters; and that the minimum, mean, and maximum sea ice extent may respond to a separate set of climatic/geochemical parameters.” Newton de Magalhães Neto, Heitor Evangelista, Kenny Tanizaki-Fonseca, Margareth Simões Penello Meirelles and Carlos Eiras Garcia, Climate Dynamics, DOI: 10.1007/s00382-011-1162-6.

Ozone over Iberian peninsula seems to be increasing

Long-Term Trends Of Total Ozone Column Over The Iberian Peninsula For The Period 1979-2008 – Antón et al. (2011) “The objective of this work is to analyze the total ozone column (TOC) trends over the Iberian Peninsula during the last 30 years (1979-2008). This study is carried out using TOC data derived from the Multi Sensor Reanalysis (MSR), Total Ozone Mapping Spectrometer (TOMS) and Global Ozone Monitoring Experiment (GOME). The analysis of the long-term ozone trends is focused on two sub-periods (1979-1994 and 1995-2008) in order to detect changes in the ozone trend pattern. The results show that the ozone depletion was statistically significant at the 95% confidence level during the first sub-period (1979-1994) in the entire region of study (except in the Southerner locations), with linear trends from -4.5 %/decade to -2.5 %/decade. These linear trends present a clear dependence on latitude, being higher for the Northerner locations than for the Southerner. By contrast, the analysis of the second sub-period of study (1995-2008) shows positive ozone trends over the Iberian Peninsula, with the highest values (+2.5 %/decade) in the Northeast of this region. This result indicates that the ozone layer may be responding as expected to the controls on ozone-depleting substances imposed by the Montreal Protocol. Additionally, a seasonal trend analysis is performed using the average of the deseasonalized monthly values for each season of the year. The seasonal analysis showed that the negative ozone trends during the first sub-period of study were statistically significant in the spring and winter, while that the seasonal ozone trends obtained during the second sub-period are positive but in general not significant at 95%.” M. Antón, D. Bortoli, P.S. Kulkarni, M.J. Costa, A.F. Domingues, D. Loyola, A.M. Silva and L. Alados-Arboledas, Atmospheric Environment, doi:10.1016/j.atmosenv.2011.08.058.

Great Plains of North America get some of their droughts from AMO

Key role of the Atlantic Multidecadal Oscillation in 20th century drought and wet periods over the Great Plains – Nigam et al. (2011) “The Great Plains of North America are susceptible to multi-year droughts, such as the 1930s ‘Dust Bowl’. The droughts have been linked to SST variability in the Pacific and Atlantic basins. This observationally rooted analysis shows the SST influence in multi-year droughts and wet episodes over the Great Plains to be significantly more extensive than previously indicated. The remarkable statistical reconstruction of the major hydroclimate episodes attests to the extent of the SST influence in nature, and facilitated evaluation of the basin contributions. We find the Atlantic SSTs to be especially influential in forcing multi-year droughts; often, more than the Pacific ones. The Atlantic Multidecadal Oscillation (AMO), in particular, contributed the most in two of the four reconstructed episodes (Dust Bowl Spring, 1980s fall wetness), accounting for almost half the precipitation signal in each case. The AMO influence on continental precipitation was provided circulation context from analysis of NOAA’s 20th Century Atmospheric Reanalysis. A hypothesis for how the AMO atmospheric circulation anomalies are generated from AMO SSTs is proposed to advance discussion of the influence pathways of the mid-to-high latitude SST anomalies. Our analysis suggests that the La Nina–US Drought paradigm, operative on interannual time scales, has been conferred excessive relevance on decadal time scales in the recent literature.” Nigam, S., B. Guan, and A. Ruiz-Barradas (2011), Geophys. Res. Lett., 38, L16713, doi:10.1029/2011GL048650.

Lake Chad – ex-giant lake

On the causes of the shrinking of Lake Chad – Gao et al. (2011) “Over the last 40 years, Lake Chad, once the sixth largest lake in the world, has decreased by more than 90% in area. In this study, we use a hydrological model coupled with a lake/wetland algorithm to simulate the effects of lake bathymetry, human water use, and decadal climate variability on the lake’s level, surface area, and water storage. In addition to the effects of persistent droughts and increasing irrigation withdrawals on the shrinking, we find that the lake’s unique bathymetry—which allows its division into two smaller lakes—has made it more vulnerable to water loss. Unfortunately the lake’s split is favored by the 1952–2006 climatology. Failure of the lake to remerge with renewed rainfall in the 1990s following the drought years of the 1970s and 1980s is a consequence of irrigation withdrawals. Under current climate and water use, a full recovery of the lake is unlikely without an inter-basin water transfer. Breaching the barrier separating the north and south lakes would reduce the amount of supplemental water needed for recovery.” H Gao et al 2011 Environ. Res. Lett. 6 034021 doi: 10.1088/1748-9326/6/3/034021. [Full text]

Climate change is critical issue for wine industry

A need for planned adaptation to climate change in the wine industry – Metzger & Rounsevell (2011) No abstract. Marc J Metzger and Mark D A Rounsevell 2011 Environ. Res. Lett. 6 031001 doi: 10.1088/1748-9326/6/3/031001. [Full text]

Eocene El Niño might not have been permanent

El Niño in the Eocene greenhouse recorded by fossil bivalves and wood from Antarctica – Ivany et al. (2011) “Quasi-periodic variation in sea-surface temperature, precipitation, and sea-level pressure in the equatorial Pacific known as the El Niño – Southern Oscillation (ENSO) is an important mode of interannual variability in global climate. A collapse of the tropical Pacific onto a state resembling a so-called ‘permanent El Niño’, with a preferentially warmed eastern equatorial Pacific, flatter thermocline, and reduced interannual variability, in a warmer world is predicted by prevailing ENSO theory. If correct, future warming will be accompanied by a shift toward persistent conditions resembling El Niño years today, with major implications for global hydrological cycles and consequent impacts on socioeconomic and ecological systems. However, much uncertainty remains about how interannual variability will be affected. Here, we present multi-annual records of climate derived from growth increment widths in fossil bivalves and co-occurring driftwood from the Antarctic peninsula that demonstrate significant variability in the quasi-biennial and 3–6 year bands consistent with ENSO, despite early Eocene (∼50 Mya) greenhouse conditions with global average temperature ∼10 degrees higher than today. A coupled climate model suggests an ENSO signal and teleconnections to this region during the Eocene, much like today. The presence of ENSO variation during this markedly warmer interval argues for the persistence of robust interannual variability in our future greenhouse world.” Ivany, L. C., T. Brey, M. Huber, D. P. Buick, and B. R. Schöne (2011), Geophys. Res. Lett., 38, L16709, doi:10.1029/2011GL048635.

Some coral reefs might be able to partially compensate for ocean acidification

Coral Reefs Modify Their Seawater Carbon Chemistry – Case Study from a Barrier Reef (Moorea, French Polynesia) – Kleypas et al. (2011) “Changes in the carbonate chemistry of coral reef waters is driven by carbon fluxes from two sources: concentrations of CO2 in the atmospheric and source water, and the primary production/respiration and calcification/dissolution of the benthic community. Recent model analyses have shown that, depending on the composition of the reef community, the air-sea flux of CO2 driven by benthic community processes can exceed that due to increases in atmospheric CO2 (ocean acidification). We field test this model and examine the role of three key members of benthic reef communities in modifying the chemistry of the ocean source water: corals, macroalgae and sand. Building on data from previous carbon flux studies along a reef-flat transect in Moorea (French Polynesia), we illustrate that the drawdown of total dissolved inorganic carbon (CT) due to photosynthesis and calcification of reef communities can exceed the draw down of total alkalinity (AT) due to calcification of corals and calcifying algae, leading to a net increase in aragonite saturation state (Ωa). We use the model to test how changes in atmospheric CO2 forcing and benthic community structure affect the overall calcification rates on the reef flat. Results show that between the preindustrial period and 1992, ocean acidification caused reef flat calcification rates to decline by an estimated 15%, but loss of coral cover caused calcification rates to decline by at least three times that amount. The results also show that the upstream-downstream patterns of carbonate chemistry were affected by the spatial patterns of benthic community structure. Changes in the ratio of photosynthesis to calcification can thus partially compensate for ocean acidification, at least on shallow reef flats. With no change in benthic community structure, however, ocean acidification depressed net calcification of the reef flat consistent with findings of previous studies.” Joan A. Kleypas, Kenneth R. N. Anthony, Jean-Pierre Gattuso, Global Change Biology, DOI: 10.1111/j.1365-2486.2011.02530.x.

Relation of extreme precipitation and surface temperature globally

Does higher surface temperature intensify extreme precipitation? – Utsumi et al. (2011) “Recently, against the backdrop of current climate, several regional studies have investigated the applicability of the Clausius–Clapeyron relation to the scaling relationship between extreme precipitation intensity and surface air temperature. Nevertheless, the temperature relationship of the extreme precipitation intensity on a global scale is still unclear. We assess, for the first time, the global relationship between the extreme daily precipitation intensity and the daily surface air temperature using in-situ data. The extreme daily precipitation intensity increased monotonically with the daily surface air temperature at high latitudes and decreased monotonically in the tropics. Similarly, the extreme daily precipitation intensity at middle latitudes increased at low temperatures and decreased at high temperatures; this decrease could be largely attributed to the decrease in the wet-event duration. The Clausius–Clapeyron scaling is applicable to the increase in the extreme daily precipitation intensity in a limited number of regions. However, the potential applicability of the Clausius–Clapeyron scaling on sub-hourly timescale was observed, even in regions where the Clausius–Clapeyron scaling on daily timescale was not applicable. This implies the potential of warming to intensify extreme precipitation on sub-hourly timescales.” Utsumi, N., S. Seto, S. Kanae, E. E. Maeda, and T. Oki (2011), Geophys. Res. Lett., 38, L16708, doi:10.1029/2011GL048426.

Earth’s surface energy has increased when all energy components are considered

Observed changes in surface atmospheric energy over land – Peterson et al. (2011) “The temperature of the surface atmosphere over land has been rising during recent decades. But surface temperature, or, more accurately, enthalpy which can be calculated from temperature, is only one component of the energy content of the surface atmosphere. The other parts include kinetic energy and latent heat. It has been advocated in certain quarters that ignoring these additional terms somehow calls into question global surface temperature analyses. Examination of all three of these components of atmospheric energetics reveals a significant increase in global surface atmospheric energy since the 1970s. Kinetic energy has decreased but by over two orders of magnitude less than the increases in both enthalpy and latent heat which provide approximately equal contributions to the global increases in heat content. Regionally, the enthalpy or the latent heat component can dominate the change in heat content. Although generally changes in latent heat and enthalpy act in concert, in some regions they can have the opposite signs.” Peterson, T. C., K. Willett, and P. W. Thorne (2011), Geophys. Res. Lett., doi:10.1029/2011GL048442.

TSI difference between recent minimum and Maunder mimimum is likely small

Are the most recent estimates for Maunder Minimum solar irradiance in agreement with temperature reconstructions? – Feulner (2011) “Estimates for the total solar irradiance (TSI) during the 17th-century Maunder Minimum published in the last few years have pointed towards a TSI difference of 0.2-0.7 W m−2 as compared to the 2008/2009 solar minimum. Two recent studies, however, give anomalies which differ from this emerging consensus. The first study indicates an even smaller TSI difference, placing the Maunder Minimum TSI on the same level as the 2008/2009 minimum. The second study on the other hand suggests a very large TSI difference of 5.8 W m−2. Here I use coupled climate simulations to assess the implications of these two estimates on Northern-hemisphere surface air temperatures over the past millennium. Using a solar forcing corresponding to the estimate of the first study, simulated Northern-hemisphere temperatures over the past millennium are consistent with reconstructed surface air temperatures. The large TSI differences between times of high and low solar activity as suggested by the second study, however, yield temperatures during all past grand solar minima that are too low, an excessive variance in Northern-hemisphere temperature on timescales of 50-100 years as compared to reconstructions, and temperatures during the first half of the 20th century which are too low and inconsistent with the instrumental temperature record. In summary this suggests a more moderate TSI difference of less than 1 W m−2 and possibly as low as 0-0.3 W m−2.” Feulner, G. (2011), Geophys. Res. Lett., doi:10.1029/2011GL048529.

New laboratory measurements of water vapor self-continuum IR-absorption

Water vapor self-continuum absorption in near-infrared windows derived from laboratory measurements – Ptashnik et al. (2011) “In most near-infrared atmospheric windows, absorption of solar radiation is dominated by the water vapor self-continuum and yet there is a paucity of measurements in these windows. We report new laboratory measurements of the self-continuum absorption at temperatures between 293 and 472 K and pressures from 0.015 to 5 atm in four near-infrared windows between 1 and 4 μm (10000-2500 cm-1); the measurements are made over a wider range of wavenumber, temperatures and pressures than any previous measurements. They show that the self-continuum in these windows is typically one order of magnitude stronger than given in representations of the continuum widely used in climate and weather prediction models. These results are also not consistent with current theories attributing the self-continuum within windows to the far-wings of strong spectral lines in the nearby water vapor absorption bands; we suggest that they are more consistent with water dimers being the major contributor to the continuum. The calculated global-average clear-sky atmospheric absorption of solar radiation is increased by ≈0.75 W/m2 (which is about 1% of the total clear-sky absorption) by using these new measurements as compared to calculations with the MT_CKD-2.5 self-continuum model.” Ptashnik, I. V., R. A. McPheat, K. P. Shine, K. M. Smith, and R. G. Williams (2011), J. Geophys. Res., doi:10.1029/2011JD015603.

Analysis of cloud radiative effect

Combining satellite data and models to estimate cloud radiative effect at the surface and in the atmosphere – Allan (2011) “Satellite measurements and numerical forecast model reanalysis data are used to compute an updated estimate of the cloud radiative effect on the global multi-annual mean radiative energy budget of the atmosphere and surface. The cloud radiative cooling effect through reflection of short wave radiation dominates over the long wave heating effect, resulting in a net cooling of the climate system of − 21 Wm−2. The short wave radiative effect of cloud is primarily manifest as a reduction in the solar radiation absorbed at the surface of − 53 Wm−2. Clouds impact long wave radiation by heating the moist tropical atmosphere (up to around 40 Wm−2 for global annual means) while enhancing the radiative cooling of the atmosphere over other regions, in particular higher latitudes and sub-tropical marine stratocumulus regimes. While clouds act to cool the climate system during the daytime, the cloud greenhouse effect heats the climate system at night. The influence of cloud radiative effect on determining cloud feedbacks and changes in the water cycle are discussed.” Richard P. Allan, Meteorological Applications, Volume 18, Issue 3, pages 324–333, September 2011, DOI: 10.1002/met.285.

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