Clouds and Climate Change
Saturday, 25. July 2009, 10:08:58
The question of whether clouds act as a positive or negative feedback to climate change has been an issue for decades, and the uncertain effect of feedback between climate and clouds is one of the largest obstacles to producing more confident projections of global climate. As the earth warms under increasing greenhouse gases, it is not known whether clouds will dissipate, letting in more of the sun’s heat energy and making the earth warm even faster, or whether cloud cover will increase, blocking the Sun’s rays and actually slowing down global warming.
In a study published in the 24 July 2009 issue of Science researchers try to unravel this mystery. Using observational data collected over the last 50 years and complex climate models, the team has established that low-level stratiform clouds appear to dissipate as the ocean warms, indicating that changes in these clouds may enhance the warming of the planet. In other words the analysis indicate that clouds act as a positive feedback - at least in the studied region.
What are “low-level stratiform clouds”? Clouds can be sheetlike (stratiform) or vertical, and stratiform clouds are usually classified by level - low, medium or high. Low stratiform clouds are known as stratus.
The examined clouds were in particular marine stratiform clouds (comprising ordinary stratocumulus, cumulus under stratocumulus, fair-weather stratus, and badweather stratus) over the Pacific Ocean.
One key finding in the study is that it is not the warming of the ocean alone that reduces cloudiness - a weakening of the trade winds also appears to play a critical role. All models predict a warming ocean, but if they don't have the correct relationship between clouds and atmospheric circulation, they won't produce a realistic cloud response.
Reference:
Clement et al.
Observational and Model Evidence for Positive Low-Level Cloud Feedback
Science 24 July 2009:
Vol. 325. no. 5939, pp. 460 - 464
DOI: 10.1126/science.1171255
• http://www.sciencemag.org/cgi/content/abstract/325/5939/460
• http://www.rsmas.miami.edu/pressreleases/20090723-clouds.html
• http://www.sciencedaily.com/releases/2009/07/090723141812.htm
• http://www.terradaily.com/reports/Consulting_With_Clouds_999.html
In a study published in the 24 July 2009 issue of Science researchers try to unravel this mystery. Using observational data collected over the last 50 years and complex climate models, the team has established that low-level stratiform clouds appear to dissipate as the ocean warms, indicating that changes in these clouds may enhance the warming of the planet. In other words the analysis indicate that clouds act as a positive feedback - at least in the studied region.
What are “low-level stratiform clouds”? Clouds can be sheetlike (stratiform) or vertical, and stratiform clouds are usually classified by level - low, medium or high. Low stratiform clouds are known as stratus.The examined clouds were in particular marine stratiform clouds (comprising ordinary stratocumulus, cumulus under stratocumulus, fair-weather stratus, and badweather stratus) over the Pacific Ocean.
One key finding in the study is that it is not the warming of the ocean alone that reduces cloudiness - a weakening of the trade winds also appears to play a critical role. All models predict a warming ocean, but if they don't have the correct relationship between clouds and atmospheric circulation, they won't produce a realistic cloud response.
Reference:
Clement et al.
Observational and Model Evidence for Positive Low-Level Cloud Feedback
Science 24 July 2009:
Vol. 325. no. 5939, pp. 460 - 464
DOI: 10.1126/science.1171255
• http://www.sciencemag.org/cgi/content/abstract/325/5939/460
• http://www.rsmas.miami.edu/pressreleases/20090723-clouds.html
• http://www.sciencedaily.com/releases/2009/07/090723141812.htm
• http://www.terradaily.com/reports/Consulting_With_Clouds_999.html
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