March 30, 2012

expert reaction to modelling global warming to 2050

A paper in the journal Nature Geoscience predicted that climate warming by 2050 is likely to be between 1.4 and 3 °C, which is broadly consistent with the expert assessment of the Intergovernmental Panel on Climate Change.

Professor Gabriele C. Hegerl, Professor of Climate System Science at the University of Edinburgh, said:

“I think it’s a very nice paper. For the IPCC 2007 estimate of the uncertainty range of future global mean warming we arrived at an overall estimate from modelling studies and from studies based on observed changes in the 20th century. That was a major advance compared to a modelling only uncertainty range.

“The new study uses one modelling framework, accounts for many important uncertainties, and applies the observations as a sieve to pick realistic model configurations, as shown nicely in the perspective piece. So it does the things we did, but does them in one consistent approach rather than lots of separate ones. I agree with the perspective that of course this isn’t the last word – there is uncertainty in the structure, components, and resolution of the model used which isn’t accounted for. But it is an important step towards estimating uncertainty more comprehensively. The runs will also offer a great opportunity for impact studies that look at plausible ranges of future warming on scales of large regions.”

Prof Corinne Le Quéré, Director of the Tyndall Centre for Climate Change Research at the University of East Anglia, said:

“This new study makes good use of recent observations to constrain climate projections to 2050, by identifying model projections that are most consistent with recent trends. These results are very promising. Better constrained climate projections are needed to help plan a wide range of adaptation measures, from sea defences to water storage capacity and biodiversity conservation areas.”

Dr Paul Williams, Royal Society University Research Fellow in climate modelling at the University of Reading, said:

“Modelling is sometimes unfairly singled out for criticism, as though it is no more than guesswork. Certain people have a habit of criticising climate models but accepting without question the predictions of, for example, economic and epidemiological models. In reality, all models have uncertainties. However, climate models are based on well-established physics, and arguably have the stronger foundations. This thorough scientific paper is a case in point and underlines the importance of modelling to predict complex climatic changes.”

rof Julian Hunt, Emeritus Professor of Climate Modelling at University College London, said:

“I have reservations about relying on a model that combines land temperatures – which are clearly rising – with sea temperatures which can be subject to big decadal fluctuations. For example, over the past 12 years we have seen the average surface temperature of the oceans dominated by cooling in the eastern Pacific, as local weather conditions drive the cooler water towards the ocean surface. Ocean models for surface waters are not yet reliable for decadal time scales. But the deeper ocean has most certainly been warming and the sea level has been rising.

“The higher ranges given in this paper look increasingly likely, but for three additional reasons. First, current and previous models do not account for methane, a particularly powerful greenhouse gas, the release of which is now verified on land and sea. Second, they do not account for massive changes in surface albedo (reflection of light) – for example, temperature in China has increased by 2C in less than 50 years, partly due to desertification according to Chinese scientists. And third, ironically, reduced air pollution in China and India means temperatures will increase still further as there are fewer particulates shielding the earth from the sun’s energy.

“I am surprised the authors did not focus on the easier problem of studying the trends in the global average land surface temperatures, which have been rising and will continue to rise, especially with the factors I have mentioned above.”

‘Broad range of 2050 warming from an observationally constrained large climate model ensemble’ by Daniel J. Rowlands et al., published in Nature Geoscience on Sunday 25 March 2012.