June 1, 2015

expert reaction to new research on climate change and African rainfall

The effect of climate change on rainfall in the Sahel area of Africa has been examined in a paper published in the journal Nature Climate Change, with the authors using modelling to estimate the causes of recovery from drought.

Prof. Doug Parker, Professor of Meteorology at the University of Leeds, said:

“This study re-emphasises the sensitivity of the Sahelian climate to global change. But I would treat the results with great caution because we know that our global models have fundamental biases in their representation of rainfall and atmospheric circulation in this region – as in all the monsoon regions. In fact, the authors themselves note the caution which must be applied to interpreting these results. For future climate, some models predict increases and some predict decreases in rainfall for the Sahel, and we don’t know why.

“Yes, the rainfall has recovered somewhat from the droughts of the 70s and 80s; but there is also evidence of much more severe storms, causing big flooding events and crop damage. It’s a complicated story. There is a danger from the university press release of people having a false impression that we now understand future rainfall in the Sahel, when we really don’t.

“The idea that greenhouse gases have been good for the Sahel must be handled carefully: it may be true but we have to be very careful if we let the idea influence policy based on evidence from just this one model (which like other models has major biases for the Sahel).”

Dr Peter Stott, Head of Climate Monitoring and Attribution at the Met Office Hadley Centre, said:

“This important study by Buwen Dong and Rowan Sutton investigates a particular aspect of how human-induced climate change is having a major impact on the rainfall patterns we all depend on to water our crops and supply us with fresh water. The authors show new evidence for why rainfall in the Sahel region of Africa has recovered partially from the devastating drought of the 1970s and 80s and the resultant famine with increasing greenhouse gases behind much of the recovery.

“However, this does not mean that continuing greenhouse gas emissions are good for Africa or elsewhere. Further emissions are projected to lead to substantial reductions in rainfall in Southern Africa and the Mediterranean region, but substantial increases in the frequency of downpours and floods worldwide.”

Dr Matthew Watson, Reader in Natural Hazards at the University of Bristol, said:

“This paper presents the rather surprising model result that, when all the drivers of rainfall in Sub-Saharan Africa are considered in isolation, it is greenhouse gases directly that contribute most to recent observed increases in Sahelian precipitation: previous work implicated increasing sea surface temperatures as opposed to the radiative forcing effects directly.

“It is an interesting paper that makes an important contribution to the thinking on climate change. However, it will be read by some as an opportunity to cast doubt on the negative impacts of climate change. This would be a mistake. Whilst there will be positives to climate change, almost all research suggests most will be short lived if we continue on our current path. The authors themselves are exceptionally careful when describing these results in context and cite the fact that what they have really shown is that these accidental improvements were not well understood and that we are already having profound influence on the climate system, particularly in the Sahel.”

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

“This result seems interesting as it runs contrary to our existing expectations that past sea surface temperatures drove most of the rainfall changes over the Sahel. Earlier work has already linked increases in aerosols (from industrial sources) to increased drought conditions in the 1970s and 1980s, so there is now a suggestion of a human role in both the onset and recovery, though via different mechanisms.

“If, as this new study suggests, the Sahel rainfall can also respond directly to greenhouse gas warming, this represents a challenge for our ability to predict future changes as it increases the number of factors and mechanisms that we will need to correctly account for in any prediction system. ”

Prof. Mike Hulme, Professor of Climate and Culture at King’s College London, said:

“Rainfall in the African Sahel, upon which tens of millions of people depend, is notoriously variable and difficult to predict. This new study further emphasises the complex interaction of natural and human, local and global, factors which influence the decadal-scale variability of these rains.

“One should continue to remain sceptical of overconfident claims that ‘climate change’ (by which is meant fossil fuel emissions) always causes negative effects in these African drylands. Even more should one be sceptical of claims that attribute specific droughts or floods in this region to single causes, whether they be human or natural. This study is highly relevant for the ‘loss and damage’ agenda of the climate negotiations and also for the argument about whether solar climate engineering could ever be a sensible technology to implement.”

Prof. Piers Forster, Professor of Climate Change at the University of Leeds, said:

“This is an interesting study with a global-scale model, confirming that climate change will bring – and may already have caused – complex regional changes in rainfall. However, I would view their conclusions about the Sahel with extreme caution. Work done at Leeds has shown that better models which explicitly represent convection have very different patterns of rainfall change. In particular, such global models fail to capture the afternoon convective storms that are so important for rainfall in the region.”

‘Dominant role of greenhouse gas forcing in the recovery of Sahel rainfall’ by Buwen Dong and Rowan Sutton published in Nature Climate Change on Monday 1 June 2015. 

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