Some scientists have argued from observations that global warming will alter clouds in ways that will largely counter warming by greenhouse gases. But the overwhelming majority of climate scientists sides with the models, which show clouds changing in ways that amplify warming, not dampen it. Whom to believe? To help sort it out, a climate researcher looked at the example of El Niño and La Niña, naturally occurring weather patterns that cause warming (El Niño) and cooling (La Niña) in the tropical Pacific and around the globe. In a report on page 1523 of this week's issue of Science, he analyzes how they have actually influenced clouds and concludes that—at least on the scale of decades—clouds do not counter warming.
Full story at http://www.sciencemag.org/cgi/content/full/330/6010/1465?sa_campaign=Email/sntw/10-December-2010/10.1126/science.330.6010.1465