Wednesday, June 18, 2008

Global Warming Forecast: Partly Cloudy

source: http://www.usatoday.com/weather/climate/globalwarming/2008-06-18-clouds-climate_N.htm

How clouds respond to global warming poses a huge challenge for climate scientists, since clouds are far more changeable in real life than models can predict. However, experts do agree that the level of future global warming greatly depends on clouds.

A new study finds that natural variations in how clouds form could actually be causing temperature changes, rather than the other way around, and could also lead to overestimates of how sensitive the Earth's climate is to greenhouse gas emissions.

"Since the cloud changes could conceivably be caused by known long-term modes of climate variability, such as the Pacific Decadal Oscillation, or El Ni�o and La Ni�a, some, or even most, of the global warming seen in the last century could simply be due to natural fluctuations in the climate system," says lead author Roy Spencer of the University of Alabama-Huntsville.

Spencer and his co-author William Braswell point out that the paper doesn't disprove the theory that humans are causing global warming. Instead, they report that "it offers an alternative explanation for what we see in the climate system which has the potential for greatly reducing estimates of mankind's impact on Earth's climate."

"But we really won't know until much more work is done," he added. In addition to this article, Spencer has published several others that question the scientific consensus about climate change, which states that human-produced greenhouse gases such as carbon dioxide are causing global warming.

The study appears in an upcoming issue of Journal of Climate.

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