AGW Observer

Observations of anthropogenic global warming

New research from last week 6/2011

Posted by Ari Jokimäki on February 14, 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:

Caribbean coral reefs vanishing in simulations

Modeling regional coral reef responses to global warming and changes in ocean chemistry: Caribbean case study – Buddemeier et al. (2011) “Climatic change threatens the future of coral reefs in the Caribbean and the important ecosystem services they provide. We used a simulation model [Combo (“COral Mortality and Bleaching Output”)] to estimate future coral cover in the part of the eastern Caribbean impacted by a massive coral bleaching event in 2005. Combo calculates impacts of future climate change on coral reefs by combining impacts from long-term changes in average sea surface temperature (SST) and ocean acidification with impacts from episodic high temperature mortality (bleaching) events. We used mortality and heat dose data from the 2005 bleaching event to select historic temperature datasets, to use as a baseline for running Combo under different future climate scenarios and sets of assumptions. Results suggest a bleak future for coral reefs in the eastern Caribbean. For three different emissions scenarios from the Intergovernmental Panel on Climate Change (IPCC; B1, A1B, and A1FI), coral cover on most Caribbean reefs is projected to drop below 5% by the year 2035, if future mortality rates are equivalent to some of those observed in the 2005 event (50%). For a scenario where corals gain an additional 1–1.5°C of heat tolerance through a shift in the algae that live in the coral tissue, coral cover above 5% is prolonged until 2065. Additional impacts such as storms or anthropogenic damage could result in declines in coral cover even faster than those projected here. These results suggest the need to identify and preserve the locations that are likely to have a higher resiliency to bleaching to save as many remnant populations of corals as possible in the face of projected wide-spread coral loss.” R. W. Buddemeier, Diana R. Lane and J. A. Martinich, Climatic Change, DOI: 10.1007/s10584-011-0022-z. [full text]

Determining causes for spring advancement in North America

Northern Hemisphere Modes of Variability and the Timing of Spring in Western North America – Ault et al. (2011) “Spatial and temporal patterns of variability in spring onset are identified across western North America using a spring index (SI) model based on weather station Tmin and Tmax. Principal component analysis shows that two significant and independent patterns explain roughly half of the total variance in the timing of spring onset from 1920–2005. However, these patterns of spring onset do not appear to be linear responses to the primary modes of variability in the Northern Hemisphere: the Pacific-North American pattern (PNA) and the northern annular mode (NAM). Instead, over the period when reanalysis data and the spring index model overlap (1950–2005), the patterns of spring onset are local responses to the state of both the PNA and NAM, which together modulate the onset date of spring by 10 to 20 days on interannual timescales. They do so by controlling the number and intensity of warm days. There is also a region-wide trend in spring advancement of about −1.5 days per decade from 1950–2005. Trends in the NAM and PNA can only explain about one third (−0.5 days per decade) of this trend.” Toby R. Ault and Alison K. Macalady, Gregory T. Pederson, Julio L. Betancourt, Mark D. Schwartz, Journal of Climate 2011.

Solar irradiance at the South Pole

Solar irradiance at the earth’s surface: long-term behavior observed at the South Pole – Frederick & Hodge (2011) “This research examines a 17-year database of UV-A (320–400 nm) and visible (400–600 nm) solar irradiance obtained by a scanning spectroradiometer located at the South Pole. The goal is to define the variability in solar irradiance reaching the polar surface, with emphasis on the influence of cloudiness and on identifying systematic trends and possible links to the solar cycle. To eliminate changes associated with the varying solar elevation, the analysis focuses on data averaged over 30–35 day periods centered on each year’s austral summer solstice. The long-term average effect of South Polar clouds is a small attenuation, with the mean measured irradiances being about 5–6% less than the clear-sky values, although at any specific time clouds may reduce or enhance the signal that reaches the sensor. The instantaneous fractional attenuation or enhancement is wavelength dependent, where the percent deviation from the clear-sky irradiance at 400–600 nm is typically 2.5 times that at 320–340 nm. When averaged over the period near each year’s summer solstice, significant correlations appear between irradiances at all wavelengths and the solar cycle as measured by the 10.7 cm solar radio flux. An approximate 1.8 ± 1.0% decrease in ground-level irradiance occurs from solar maximum to solar minimum for the wavelength band 320–400 nm. The corresponding decrease for 400–600 nm is 2.4 ± 1.9%. The best-estimate declines appear too large to originate in the sun. If the correlations have a geophysical origin, they suggest a small variation in atmospheric attenuation with the solar cycle over the period of observation, with the greatest attenuation occurring at solar minimum.” Frederick, J. E. and Hodge, A. L., Atmos. Chem. Phys., 11, 1177-1189, doi:10.5194/acp-11-1177-2011, 2011. [full text]

Global analysis of anthropogenic sulfur dioxide emissions

Anthropogenic sulfur dioxide emissions: 1850–2005 – Smith et al. (2011) “Sulfur aerosols impact human health, ecosystems, agriculture, and global and regional climate. A new annual estimate of anthropogenic global and regional sulfur dioxide emissions has been constructed spanning the period 1850–2005 using a bottom-up mass balance method, calibrated to country-level inventory data. Global emissions peaked in the early 1970s and decreased until 2000, with an increase in recent years due to increased emissions in China, international shipping, and developing countries in general. An uncertainty analysis was conducted including both random and systemic uncertainties. The overall global uncertainty in sulfur dioxide emissions is relatively small, but regional uncertainties ranged up to 30%. The largest contributors to uncertainty at present are emissions from China and international shipping. Emissions were distributed on a 0.5° grid by sector for use in coordinated climate model experiments.” Smith, S. J., van Aardenne, J., Klimont, Z., Andres, R. J., Volke, A., and Delgado Arias, S., Atmos. Chem. Phys., 11, 1101-1116, doi:10.5194/acp-11-1101-2011, 2011. [full text]

Early anthropogenic effect on atmospheric CH4 and CO2

Can natural or anthropogenic explanations of late-Holocene CO2 and CH4 increases be falsified? – Ruddiman et al. (2011) “Concentrations of CO2 and CH4 in the atmosphere rose slowly during the millennia prior to the industrial era. Opposing explanations for these increases have invoked natural and anthropogenic sources. Here we revisit this argument using new evidence to see whether either explanation can be falsified (disproven, in the sense proposed by German philosopher Karl Popper). Two lines of evidence suggest that natural explanations for the CH4 increase are falsified: (1) the absence of any sustained methane increase early in seven interglaciations prior to the Holocene; and (2) weakening emissions during the last 5000 years from the two largest global sources of CH4– north tropical and boreal wetlands. Consistent with this interpretation, a new synthesis of archeological data from southern Asia reported in this issue indicates an exponential increase in CH4 emissions from expanding rice irrigation during the last 5000 years. Neither the anthropogenic nor the natural explanations for the CO2 increase can at this point be falsified. Previous studies that rejected the early anthropogenic hypothesis based on the small size of early farming populations ignored a rich array of archeological and historical evidence showing that early farmers used much more land per capita than those in the centuries just before the industrial era. Previous interpretations of very small terrestrial (anthropogenic and other) carbon emissions during the last 7000 years based on the δ13CO2 record failed to incorporate credible estimates of very large carbon burial in boreal peat lands during the late Holocene. Allowance for larger burial in peat deposits requires much greater emissions of anthropogenic carbon to balance the δ13CO2 budget. The prevalence of downward CO2 trends during equivalent intervals early in previous interglaciations poses a major problem for natural explanations of the late-Holocene CO2 increase.” W. F. Ruddiman, J. E. Kutzbach, S. J. Vavrus, The Holocene February 8, 2011, doi: 10.1177/0959683610387172.

Observations of seasonal changes in Titan

Seasonal changes in Titan’s meteorology – Turtle et al. (2011) “The Cassini Imaging Science Subsystem has observed Titan for ∼1/4 Titan year, and we report here the first evidence of seasonal shifts in preferred locations of tropospheric methane clouds. South-polar convective cloud activity, common in late southern summer, has become rare. North-polar and northern mid-latitude clouds appeared during the approach to the northern spring equinox in August 2009. Recent observations have shown extensive cloud systems at low latitudes. In contrast, southern mid-latitude and subtropical clouds have appeared sporadically throughout the mission, exhibiting little seasonality to date. These differences in behavior suggest that Titan’s clouds, and thus its general circulation, are influenced by both the rapid temperature response of a low-thermal-inertia surface and the much longer radiative timescale of Titan’s cold thick troposphere. North-polar clouds are often seen near lakes and seas, suggesting that local increases in methane concentration and/or lifting generated by surface roughness gradients may promote cloud formation.” Turtle, E. P., A. D. Del Genio, J. M. Barbara, J. E. Perry, E. L. Schaller, A. S. McEwen, R. A. West, and T. L. Ray (2011), Geophys. Res. Lett., 38, L03203, doi:10.1029/2010GL046266.

Northern Ireland temperature is controlled by water vapor, sun, and GHG’s

The role of water vapor and solar radiation in determining temperature changes and trends measured at Armagh, 1881–2000 – Stanhill (2011) “A 120 year series of climate measurements at Armagh Observatory, a rural site in Northern Ireland, was analyzed to yield monthly, seasonal, and annual values of long- and short-wave irradiances which were then related to the measured changes in air temperature. Three quarters of the significant increase and large decadal variations in atmospheric long-wave radiation was associated with the concurrent changes measured in specific humidity; the remaining quarter was associated with increases in the concentrations of carbon dioxide and other anthropogenic radiatively active gases. Significant but smaller long-term decreases in short-wave solar irradiance reduced by half the net, all-wave radiation forcing at the surface. Together the changes in long- and short-wave irradiances at Armagh accounted for more than three quarters of the interannual variations in mean annual temperatures. Climate sensitivity to long-wave forcing at the surface, 0.121°C per W m−2, was 5 times greater than that to short-wave forcing, and two possible explanations for this difference, water vapor feedback and changes in atmospheric circulation, are discussed.” Stanhill, G. (2011), J. Geophys. Res., 116, D03105, doi:10.1029/2010JD014044.


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