AGW Observer

Observations of anthropogenic global warming

New research from last week 46/2010

Posted by Ari Jokimäki on November 22, 2010

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.

NOTE! From now on, I’ll start posting these as whole abstracts and in the same format as the papers are in my paperlists. That way the new papers will be easier to transfer to the lists. It also saves me the time and effort to try to say the same things in my own words. The abstracts are usually quite understandably written anyway.

Published last week:

20th century dust cooled climate

A new study has looked into the climatic effects of desert dust during the 20th century. Th net radiative effect of desert dust was found to be -0.14 ± 0.11 W/m2 (this is the difference between 1990–1999 and 1905–1914). Effect can be very strong at times:

“The estimated radiative change due to dust is especially strong between the heavily loaded 1980–1989 and the less heavily loaded 1955–1964 time periods (−0.57 ± 0.46 W/m2), which model simulations suggest may have reduced the rate of temperature increase between these time periods by 0.11 °C.”

Dust also had an effect to the ocean productivity:

“Desert dust carries iron, an important micronutrient for ocean biogeochemistry that can modulate ocean carbon storage; here we show that dust deposition trends increase ocean productivity by an estimated 6% over the 20th century, drawing down an additional 4 ppm (8 PgC) of carbon dioxide into the oceans.”

Citation: Mahowald, N. M., Kloster, S., Engelstaedter, S., Moore, J. K., Mukhopadhyay, S., McConnell, J. R., Albani, S., Doney, S. C., Bhattacharya, A., Curran, M. A. J., Flanner, M. G., Hoffman, F. M., Lawrence, D. M., Lindsay, K., Mayewski, P. A., Neff, J., Rothenberg, D., Thomas, E., Thornton, P. E., and Zender, C. S.: Observed 20th century desert dust variability: impact on climate and biogeochemistry, Atmos. Chem. Phys., 10, 10875-10893, doi:10.5194/acp-10-10875-2010, 2010. [abstract, full text]

Anthropogenic aerosols might cool Arctic after all

Current thinking is that anthropogenic aerosols indirect cloud effect might have increased surface temperatures in the Arctic. Previous studies have concentrated on the longwave processes regionally. New study is making an effort to estimate the full situation including the shortwave effects for the whole Arctic area. They use climate model simulations in their study. The result:

“Results show that the longwave indirect effect at the surface lies between 0.10 and 0.85 W/m2 averaged annually north of 71°N, while the shortwave indirect effect lies between −1.29 W/m2 and −0.52 W/m2. Due to longwave dominance in winter, 6 of 11 simulations give a positive change in net cloud forcing between October and May (−0.16 to 0.29 W/m2), while the change in forcing averaged over the summer months is negative for all model simulations (from −2.63 to −0.23 W/m2). The annually averaged change in net cloud forcing at the surface is negative in 10 of 11 simulations, lying between −0.98 and 0.12 W/m2. In conclusion, our results point to a small decrease in the surface radiative flux due to the aerosol indirect effect in the Arctic, but these estimates are subject to uncertainties in the frequency of thin clouds and biases in the estimated cloud cover.”

Citation: Alterskjær, K., J. E. Kristjánsson, and C. Hoose (2010), Do anthropogenic aerosols enhance or suppress the surface cloud forcing in the Arctic?, J. Geophys. Res., 115, D22204, doi:10.1029/2010JD014015. [abstract]

New global upper air dataset reaches back to 1918

REC2 is the name for the new product that offers upper-air observation-based estimates of some weather parameters, including temperature, between 1918 and 1957. So far similar data sets have reached back to 1948 at best so this seems to be considerable improvement to that situation. there is some problems with the sparsity of the data, especially in early years, but still:

“We show the results of several validation experiments, compare our new data set with a number of existing data sets, and demonstrate that it is suitable for analysing large-scale climate variability on interannual time-scales.”

Citation: Stefan Brönnimann, Thomas Griesser and Alexander Stickler, A gridded monthly upper-air data set from 1918 to 1957, 2010, Climate Dynamics, DOI: 10.1007/s00382-010-0940-x. [abstract]

Troposphere temperature trends – review

A new review article has looked at 195 research articles on tropospheric temperatures. They find that observations show troposphere warming as expected both theoretically and in climate models.

Citation: Peter W. Thorne, John R. Lanzante, Thomas C. Peterson, Dian J. Seidel, Keith P. Shine, Tropospheric temperature trends: history of an ongoing controversy, 2010, Wiley Interdisciplinary Reviews: Climate Change, DOI: 10.1002/wcc.80. [abstract, full text, NOAA press release]

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