Recent climate models from multiple organizations project that the amount of warming that doubling atmospheric carbon dioxide would cause would be much more than previously estimated.  And one of the significant changes to the models relates to the role of clouds.

Clouds have long been a major uncertainty in climate

calculations.  Clouds can shade the earth

and thereby provide cooling.  But clouds

can also trap heat.  Which effect

dominates depends on how reflective the clouds are, how high up they are, and

whether it is day or night.  The dynamics

of clouds are complicated.

If you fly across the ocean, you will see blankets of low clouds

extending for hundreds of miles.  These

marine stratus and stratocumulus clouds predominantly cool the Earth.  In fact, they shade roughly a fifth of the

oceans and reflect 30-60% of the solar radiation that hits them back into

space.

Recent studies indicate that as global temperatures rise, these clouds

are likely to become thinner or burn off entirely, leaving more clear skies

through which the sun may add another degree Celsius or more to global warming.

The concerns about clouds are part of the larger issue about feedbacks

in warming the world.  It has long been

clear that the greenhouse effect of doubling CO2 levels in the atmosphere would

raise global temperature.  But there are

amplifying feedback effects.  Melting

large areas of snow and ice reduces reflectivity and allows the land and oceans

to absorb more heat.  More water vapor

entering the atmosphere traps more heat. 

And now clouds are another concern.

Overall, these effects are leading to climate models predicting much

larger global temperature increases, which is a scary prospect for the world.

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Why Clouds Are the Key to New Troubling Projections on Warming

Photo, posted September 10, 2006, courtesy of Nicholas A. Tonelli via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.