Washington — Scientists have come up with a possible explanation for why the rise in Earth’s temperature paused for a bit during the 2000s, one of the hottest decades on record.
The answer seems counterintuitive. It’s all that sulfur pollution in the air from China’s massive coal-burning, according to a new study.
Sulfur particles in the air deflect the sun’s rays and can temporarily cool things down a bit. That can happen even as coal-burning produces the carbon dioxide that contributes to global warming.
“People normally just focus on the warming effect of CO2 (carbon dioxide), but during the Chinese economic expansion there was a huge increase in sulfur emissions,” which have a cooling effect, explained Robert K. Kaufmann of Boston University. He’s the lead author of the study published Monday in Proceedings of the National Academy of Science.
But sulfur’s cooling effect is only temporary, while the carbon dioxide from coal burning stays in Earth’s atmosphere a long time.
Chinese coal consumption doubled between 2003 and 2007, and that caused a 26 percent increase in global coal consumption, Kaufmann said.
Now, Chinese leaders have recognized the effects of that pollution on their environment and their citizens’ health and are installing equipment to scrub out the sulfur particles, Kaufmann said.
Sulfur quickly drops out of the air if it is not replenished, while carbon dioxide remains for a long time, so its warming effects are beginning to be visible again, he noted. The plateau in temperature growth disappeared in 2009 and 2010, when temperatures lurched upward.
Indeed, NASA and the National Oceanic and Atmospheric Administration, have listed 2010 as tied for the warmest year on record, while the Hadley Center of the British Meteorological Office lists it as second warmest, after 1998.