"In order to better understand climate change, we need to turn our attention towards understanding very clean regions of the atmosphere—as might have existed in the mid-1700s," says Ken Carslaw. "Such regions are incredibly rare now, but we are looking for them." (Credit: sukhchander/Flickr)

Rare ‘clean’ skies could help predict future climate

Natural emissions, like those from volcanoes or plants, may add to the uncertainty of how climate responds to greenhouse gas emissions.

A new study shows that the effect of aerosols on the climate since industrialization depends strongly on what the atmosphere was like before man-made pollution—when aerosols were only produced from these natural emissions.

“We have shown that our poor knowledge of aerosols prior to the industrial revolution dominates the uncertainty in how aerosols have affected clouds and climate,” says Ken Carslaw, professor from the School of Earth and Environment at the University of Leeds.

“In order to better understand climate change, we need to turn our attention towards understanding very clean regions of the atmosphere—as might have existed in the mid-1700s. Such regions are incredibly rare now, but we are looking for them.”

Bright clouds

Aerosols tend to increase the brightness of clouds, which in turn increases the reflection of solar radiation to space, thereby partially masking the climate-warming effects of greenhouse gas emissions.

Firmly establishing the effect of aerosol-induced changes on cloud brightness is an important challenge for climate scientists.

In an assessment of 28 factors that could affect the uncertainties in cloud brightness, the researchers found that 45 percent of the variance comes from natural aerosols, compared with 34 percent for human-generated aerosols.

Aerosol processes, such as how quickly they are removed from the atmosphere, account for the remaining uncertainty.

“Our results provide a clear path for scientists to reduce the uncertainty in aerosol effects on climate because we have been able to rank the causes for the uncertainty,” Carslaw says.

Source: University of Leeds

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