AGW Observer

Observations of anthropogenic global warming

New research from last week 42/2011

Posted by Ari Jokimäki on October 24, 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.

Hale cycle correlates with surface temperature better than sunspot cycle – new “it’s the sun” meme is born?

On the Relationship between Global, Hemispheric and Latitudinal Averaged Air Surface Temperature (GISS Time Series) and Solar Activity – Souza Echer et al. (2011) “The air surface temperature is a basic meteorological parameter and its variation is a primary measure of global, regional and local climate changes. In this work, the global, hemispheric and latitudinal averaged air surface temperature time series, obtained from the NASA/Goddard Institute for Space Studies (GISS), and the Sunspot Number (Rz) for the interval 1880-2005, are decomposed in frequency bands through wavelet multi-resolution analysis. We have found a very low correlation between global, hemispheric and latitudinal averaged air surface temperature and Rz in the 11 yr solar cycle band (8-16 years) from ∼1880 to ∼1950. After wards the correlation is higher. A very significant correlation (R∼0.57 to 0.80) is found in the ∼22 yr solar Hale cycle band (16-32 years) with lags from zero to four years between latitudinal air surface temperature and Rz. Therefore it seems that the 22 yr magnetic field solar cycle might have a higher effect on Earth’s climate than solar variations related to the 11 yr sunspot cycle.” M.P. Souza Echer, E. Echer, N.R. Rigozo, CGM Brum, D.J.R. Nordemann, W.D Gonzalez, Journal of Atmospheric and Solar-Terrestrial Physics, doi:10.1016/j.jastp.2011.10.002.

Lake ice duration 10-60 days shorter by 2070 in North American Arctic

The fate of lake ice in the North American Arctic – Brown & Duguay (2011) “Lakes comprise a large portion of the surface cover in northern North America, forming an important part of the cryosphere. The timing of lake ice phenological events (e.g. break-up/freeze-up) is a useful indicator of climate variability and change, which is of particular relevance in environmentally sensitive areas such as the North American Arctic. Further alterations to the present day ice regime could result in major ecosystem changes, such as species shifts and the disappearance of perennial ice cover. The Canadian Lake Ice Model (CLIMo) was used to simulate lake ice phenology across the North American Arctic from 1961–2100 using two climate scenarios produced by the Canadian Regional Climate Model (CRCM). Results from the 1961–1990 time period were validated using 15 locations across the Canadian Arctic, with both in situ ice cover observations from the Canadian Ice Database as well as additional ice cover simulations using nearby weather station data. Projected changes to the ice cover using the 30-year mean data between 1961–1990 and 2041–2070 suggest a shift in break-up and freeze-up dates for most areas ranging from 10–25 days earlier (break-up) and 0–15 days later (freeze-up). The resulting ice cover durations show mainly a 10–25 day reduction for the shallower lakes (3 and 10 m) and 10–30 day reduction for the deeper lakes (30 m). More extreme reductions of up to 60 days (excluding the loss of perennial ice cover) were shown in the coastal regions compared to the interior continental areas. The mean maximum ice thickness was shown to decrease by 10–60 cm with no snow cover and 5–50 cm with snow cover on the ice. Snow ice was also shown to increase through most of the study area with the exception of the Alaskan coastal areas.” Brown, L. C. and Duguay, C. R., The Cryosphere, 5, 869-892, doi:10.5194/tc-5-869-2011, 2011. [Full text]

Increasing water vapor causes solar radiation dimming

The roles of aerosol, water vapor and cloud in future global dimming/brightening – Haywood et al. (2011) “Observational evidence indicates significant regional trends in solar radiation at the surface in both all-sky and cloud-free conditions. Negative trends in the downwelling solar surface irradiance (SSI) have become known as ‘dimming’ while positive trends have become known as ‘brightening’. We use the Met Office Hadley Centre HadGEM2 climate model to model trends in cloud-free and total SSI from the pre-industrial to the present-day and compare these against observations. Simulations driven by CMIP5 emissions are used to model the future trends in dimming/brightening up to the year 2100. The modeled trends are reasonably consistent with observed regional trends in dimming and brightening which are due to changes in concentrations in anthropogenic aerosols and, potentially, changes in cloud cover owing to the aerosol indirect effects and/or cloud feedback mechanisms. The future dimming/brightening in cloud-free SSI is not only caused by changes in anthropogenic aerosols: aerosol impacts are overwhelmed by a large dimming caused by increases in water vapor. There is little trend in the total SSI as cloud cover decreases in the climate model used here, and compensates the effect of the change in water vapor. In terms of the surface energy balance, these trends in SSI are obviously more than compensated by the increase in the downwelling terrestrial irradiance from increased water vapor concentrations. However, the study shows that while water vapor is widely appreciated as a greenhouse gas, water vapor impacts on the atmospheric transmission of solar radiation and the future of global dimming/brightening should not be overlooked.” Haywood, J. M., N. Bellouin, A. Jones, O. Boucher, M. Wild, and K. P. Shine (2011), J. Geophys. Res., 116, D20203, doi:10.1029/2011JD016000.

A coral acclimated to ocean acidification in longer term experiment

Acclimation to ocean acidification during long-term CO2 exposure in the cold-water coral Lophelia pertusa – Form & Riebesell (2011) “Ocean acidity has increased by 30% since preindustrial times due to the uptake of anthropogenic CO2 and is projected to rise by another 120% before 2100 if CO2 emissions continue at current rates. Ocean acidification is expected to have wide-ranging impacts on marine life, including reduced growth and net erosion of coral reefs. Our present understanding of the impacts of ocean acidification on marine life, however, relies heavily on results from short-term CO2 perturbation studies. Here we present results from the first long-term CO2 perturbation study on the dominant reef-building cold-water coral Lophelia pertusa and relate them to results from a short-term study to compare the effect of exposure time on the coral’s responses. Short-term (one week) high CO2 exposure resulted in a decline of calcification by 26-29% for a pH decrease of 0.1 units and net dissolution of calcium carbonate. In contrast, L. pertusa was capable to acclimate to acidified conditions in long-term (six months) incubations, leading to even slightly enhanced rates of calcification. Net growth is sustained even in waters sub-saturated with respect to aragonite. Acclimation to seawater acidification did not cause a measurable increase in metabolic rates. This is the first evidence of successful acclimation in a coral species to ocean acidification, emphasizing the general need for long-term incubations in ocean acidification research. To conclude on the sensitivity of cold-water coral reefs to future ocean acidification further ecophysiological studies are necessary which should also encompass the role of food availability and rising temperatures.” Armin U. Form, Ulf Riebesell, Global Change Biology, DOI: 10.1111/j.1365-2486.2011.02583.x.

Another pollen reconstruction showing modern times warmer than MWP in North-America

A pollen-based reconstruction of summer temperature in central North America and implications for circulation patterns during medieval times – Wahl et al. (2011) “We present a reconstruction of mean summer temperature for the northern Midwest of the U.S.A based on lacustrine pollen records from three different lakes in Wisconsin. The results suggest a relatively warm period during the earlier part of the record (~ 1200–1500 CE) followed by a cooler Little Ice Age (~ 1500–1900) and a subsequent warming to modern conditions. The reconstructed modern summer mean temperature is in good agreement with observations, and the decades of the 1930s to 1950s appear to be the warmest such period in the proxy record (through 1974). Analyses of circulation features associated with the warmest summers in the recent climate record suggest a prevalence of continental ridging accompanied by generally dry conditions during extremely warm summers in the Midwest. Drought reconstruction using the Palmer Drought Severity Index (PDSI) and tree-ring records as predictors also yield relatively dry conditions in medieval times for the central US. As reported in a number of recent studies, possible forcing mechanisms include La Niña-like conditions in the equatorial Pacific and warmer than average waters in the tropical Indo-western Pacific Ocean possibly coupled to a positive mode of the AMO/NAO North Atlantic circulation pattern.” Eugene R. Wahl, Henry F. Diaz, Christian Ohlwein, Global and Planetary Change, doi:10.1016/j.gloplacha.2011.10.005.

East Antarctic ice accumulation changes during recent decades are largest in 800 years

Variation of accumulation rates over the last eight centuries on the East Antarctic Plateau derived from volcanic signals in ice cores – Anschütz et al. (2011) “Volcanic signatures in ice-core records provide an excellent means to date the cores and obtain information about accumulation rates. From several ice cores it is thus possible to extract a spatio-temporal accumulation pattern. We show records of electrical conductivity and sulfur from 13 firn cores from the Norwegian-USA scientific traverse during the International Polar Year 2007–2009 (IPY) through East Antarctica. Major volcanic eruptions are identified and used to assess century-scale accumulation changes. The largest changes seem to occur in the most recent decades with accumulation over the period 1963–2007/08 being up to 25% different from the long-term record. There is no clear overall trend, some sites show an increase in accumulation over the period 1963 to present while others show a decrease. Almost all of the sites above 3200 m above sea level (asl) suggest a decrease. These sites also show a significantly lower accumulation value than large-scale assessments both for the period 1963 to present and for the long-term mean at the respective drill sites. The spatial accumulation distribution is influenced mainly by elevation and distance to the ocean (continentality), as expected. Ground-penetrating radar data around the drill sites show a spatial variability within 10–20% over several tens of kilometers, indicating that our drill sites are well representative for the area around them. Our results are important for large-scale assessments of Antarctic mass balance and model validation.” Anschütz, H., A. Sinisalo, E. Isaksson, J. R. McConnell, S.-E. Hamran, M. M. Bisiaux, D. Pasteris, T. A. Neumann, and J.-G. Winther (2011), J. Geophys. Res., 116, D20103, doi:10.1029/2011JD015753.

Assumed negative feedback from Arctic winter thermal inversions is positive feeback

Arctic winter warming amplified by the thermal inversion and consequent low infrared cooling to space – Bintanja et al. (2011) “Pronounced warming in the Arctic region, coined Arctic amplification, is an important feature of observed and modelled climate change. Arctic amplification is generally attributed to the retreat of sea-ice and snow, and the associated surface-albedo feedback, in conjunction with other processes. In addition, the predominant thermal surface inversion in winter has been suggested to pose a negative feedback to Arctic warming by enhancing infrared radiative cooling. Here we use the coupled climate model EC-Earth in idealized climate change experiments to quantify the individual contributions of the surface and the atmosphere to infrared radiative cooling. We find that the surface inversion in fact intensifies Arctic amplification, because the ability of the Arctic wintertime clear-sky atmosphere to cool to space decreases with inversion strength. Specifically, we find that the cold layers close to the surface in Arctic winter, where most of the warming takes place, hardly contribute to the infrared radiation that goes out to space. Instead, the additional radiation that is generated by the warming of these layers is directed downwards, and thus amplifies the warming. We conclude that the predominant Arctic wintertime temperature inversion damps infrared cooling of the system, and thus constitutes a positive warming feedback.” R. Bintanja, R. G. Graversen & W. Hazeleger, Nature Geoscience(2011), doi:10.1038/ngeo1285.


2 Responses to “New research from last week 42/2011”

  1. Nick said

    Ari,it’s time to make my annual comment…. as usual,thanks again for this valuable resource!

  2. Ari Jokimäki said

    Thanks, Nick. 🙂

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