Heavy air pollution is slowing Global Warming.

http://blog.wired.com/wiredscience/2...air_pollu.html

These particles have a direct effect on global and regional climate by intercepting sunlight and radiating it back into space. Over the Pacific on a clear day, the plumes can cut sunlight reaching the ocean surface by 10 to 15 percent, scientists say. Globally they may be concealing as much as half the warming effect of the carbon dioxide that human industrial processes have pumped into the air since the beginning of the Industrial Revolution, researchers add.