February 16, 2011

expert reaction to two Nature papers on climate change

Two papers reveal evidence that human-induced global warming has had a direct contribution to flooding and high levels of precipitation in the UK.

Prof Nigel Arnell, Director of Walker Institute for Climate System Research, University of Reading, said:

“These two papers, using different approaches, demonstrate that it is possible to detect a human influence on the occurrence of extreme events. Until now we have only been able to say – on first principles – that climate change has made specific types of events more (or less) likely. The analysis and methods used here allow us to make more quantitative statements about the changes in the likelihood of past events. The specific results in these studies are influenced by the characteristics of the models used, but the research presented here marks a major advance in our understanding of climate change and it’s impacts here and now.”

Dr Richard Allan, Department of Meteorology, University of Reading, said:

“Observations and theory show that a warming atmosphere carries greater quantities of gaseous water vapour which fuels the most intense rainfall events. So basic physics tells us that rainfall is likely to be more intense in a warmer world and this is backed up by observational evidence and detailed simulations.

“The two studies demonstrate through careful use of observations and detailed simulations of weather patterns, rainfall distributions and river flow, that heavy rainfall events are becoming more intense and liable to cause serious damage through human-induced emissions of greenhouse gases and the associated global warming.

“Exact local changes in rainfall extremes are difficult to predict with certainty since they depend upon small shifts in atmospheric circulation systems.
However, the two studies demonstrate that a human impact upon the intensification of rainfall and associated flooding is already detectable.”

Prof Roger Pielke Jr., Professor of Environmental Studies at the University of Colorado, said:

“It is exciting to see the application of innovative approaches to connecting the dots between greenhouse gas emissions and damage from extreme events. Pall et al. seek to quantify the increased risk due to greenhouse gas emissions for a particular flood event in England and Wales in 2000. Their methodology extends an approach first applied in the context of the European heat wave of 2003. Wide acceptance of such a methodology will most likely have to await the ability to demonstrate skill in seasonal forecasting 9of the future) that improves upon methods that do not consider the influence of greenhouse gases. This is particularly the case in situations such as flooding in Wales and England, where the authors observe that the region has seen no long-term trends in either flooding or precipitation. Such important research is in its infancy.”

Prof Mark Maslin, Co-Director of the Environment Institute at University College London, said:

“Since we first recognised the threat of global warming scientists have consistently stated that no single extreme weather event can be definitively link to anthropogenic climate change. This is because there has always been extreme weather events and attributing cause of individual events is very difficult. The paper by Pall et al. in Nature fundamentally changes this. By running thousands of model runs they demonstrate that in human induced climate change did have a significant influence on the occurrence of the destructive floods in the UK in year 2000. These floods damaged nearly 10,000 properties and caused an estimated insured damages are over £1.3 billion. But this is small scale compared to the immense damage and loss of life caused by the recent floods in Pakistan, Brazil and Australia. In the same issue of Nature Min et al. has been shown that over two thirds of the extreme rainfall events over the last 50 years were made more intense by human-induced increases in greenhouse gases. These papers taken together provide a very strong scientific message to politicians that the occurrence and magnitude of huge floods around the world have been made worse by anthropogenic climate change, and there we were thinking all the effects of climate change would be in the far future.”

Prof Tim Palmer, Royal Society Research Professor in Climate Physics, University of Oxford, said:

“The papers both suggest that observed patterns of increase in extreme precipitation are broadly what we would expect, based on existing climate models forced with increased GHGs. However, there remains considerably uncertainty about the magnitude of future climate change, both regionally and globally, and these results should not be interpreted as implying that the current generation of climate models is good enough. Refining our models in order that we can simulate climate extremes with more fidelity, must be a priority for the future. A lot of this is linked with supercomputing capability and capacity.”

Prof Sir Brian Hoskins, Royal Society Research Professor at the Grantham Institute for Climate Change, and member of the new Committee on Climate Change, said:

“Increases in intense precipitation have been observed in many places, and according to basic physical ideas this would be expected to accompany global warming. For any event or period, such as Autumn 2000 in England and Wales, we have always had to make a rather vague statement that such events are more likely because of global warming but that we cannot say this particular event is because of global warming. These two papers are notable in their inventive use of climate model experiments with the aim of quantifying the link with our greenhouse gas emissions. One paper is able to ascribe much of the general increase in heavy rainfall events to human activity. The other is able to give a firm idea of the increased likelihood of our Autumn floods. However, both studies depend heavily on the accuracy of their computer models. We need to understand better the actual physics of different flooding events and make sure that the models are able to capture this. Model based studies like these should be repeated as models continue to improve.”