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While we’ve been pumping the atmosphere full of heat-trapping gases, Mother Earth has been belching sulfur pollution through volcanoes and slowing down global warming.

That’s the conclusion of a new study that’s helping to explain why the globe warmed less during the first 10 years of this century than climate models suggest it should have. If volcanic activity calms down and sulfur pollution levels fall away again, runaway global warming could ensue.

Scientists believe that elevated levels of aerosols in the stratosphere, particularly sulfuric acid and water particles formed from sulfur dioxide pollution, have been shielding the ground from solar radiation. That has helped offset the warming effects of a spike in atmospheric levels of carbon dioxide and other greenhouse gases. It was previously thought that the aerosols were perhaps being pumped into the atmosphere by industrial activity. But the new research, published in Geophysical Research Letters, suggests that the aerosols have come from a natural source. From Science NOW:

[B]y using a computer model that includes processes due to global atmospheric circulation and atmospheric chemistry, [CU-Boulder atmospheric scientist Ryan] Neely and his colleagues show that the human contribution of aerosols to the stratosphere was minimal between 2000 and 2010. In one set of simulations, the researchers estimated the effects of all known volcanic eruptions, including the quantity of aerosols produced and the heights to which they wafted, on the month-to-month variations in particulate concentrations. The pattern of stratospheric particulate variations during the past decade “shows the fingerprint of volcanoes, with the right episodes showing up at the right time,” says William Randel, an atmospheric scientist at the National Center for Atmospheric Research in Boulder. “This is very convincing to me.”

So please keep those volcanic burps coming, Mother Earth. We could use all the help we can get.