November 6, 2013

expert reaction to new paper on aerosols and climate

Natural aerosols, such as emissions from volcanoes or plants, may contribute more uncertainty than previously thought to estimates of how the climate might respond to greenhouse gas emissions, according to a study in Nature. 

Prof Alastair Lewis, Professor of Atmospheric Chemistry at the National Centre for Atmospheric Science at the University of York, said:

“Understanding the earth’s atmosphere before the industrial revolution is essential if the effects we’ve had on the planet after that point are to be assessed.  We are lucky that for the warming greenhouse gases, there are some excellent records of the atmosphere before the industrial age – for example gases trapped in ice and snow.  But much less is known about changes to aerosols and clouds, which predominately cool; unfortunately these aren’t preserved in the same way.

“As this study shows there are lots of different natural factors at play, from volcanoes to forest, which add uncertainty to the size and variability of the cooling side of the equation.  The best we can do now is try to understand the atmosphere in places where it is close to its preindustrial state.  Not easy, since aerosol pollution from man is a global phenomenon; but there are locations, always very remote, where we may get close to this.”

Dr Ben Booth, Senior Climate Scientist at the Met Office Hadley Centre, said:

 “Estimates of the effects of aerosols on climate have always been imprecise.  The better we understand their impact, the better our climate models and climate projections will be.  I welcome this new study as it helps scientists understand what are the important questions determining how the climate responds to particle pollution, emitted as a by-product of fossil fuel use.

“It’s important to note that this work does not suggest that natural forces outweigh human ones.  Instead, this study shows us that the ‘cleanness’ of the natural climate in the past has a big bearing on how sensitive the climate is to emissions of man-made aerosols.”

‘Large contribution of natural aerosols to uncertainty in indirect forcing’ by K. S. Carslaw et al. published in Nature on Wednesday 6^th November.