Select Committee on Science and Technology Minutes of Evidence

Letter to the Clerk of the Committee from Professor Alan O'Neill, NERC Centre for Global Atmospheric Modelling, University of Reading

  1.  A possible explanation for the upward trend in the earth's temperature is natural variability of the climate system (which is known to vary on a wide range of timescales). The Centre for Global Atmospheric Modelling (CGAM) investigates natural climate variability on seasonal decadal timescales, by using advanced mathematical models of the climate system. Our results do not allow us to conclude that the observed temperature rise is entirely the result of natural variability. The weight of evidence is that the rise is connected, at least in part, to the increasing concentrations of greenhouse gases in the atmosphere.

  2.  CGAM makes extensive use of the climate model developed by the Hadley Centre. The model has a number of shortcomings in common with other climate models. The greatest uncertainty is probably in the treatment of clouds (and their effect on atmospheric radiation). There is considerable research worldwide to narrow this uncertainty. Increasing computer power will be essential to progress, so that climate models can represent explicitly processes that take place on small spatial scales.

  3.  There is a broad consensus among climate scientists that increased concentrations of greenhouse gases will contribute to global warming. These scientists also recognise the importance of natural variability, and the difficulty of disentangling natural effects from anthropogenic effects from the relatively short 100-year temperature record. There is general agreement that the anthropogenic "signal" in the temperature record is beginning to rise above the "noise" of natural climate variability. A few climate scientists (some of whom are distinguished) argue that the predictions of climate models are erroneous because important feedback processes in the natural world are misrepresented in the models (eg feedback processes involving cloud and water vapour). However, these scientists have not yet adduced credible evidence that falsifies the basic prediction of global warming.

  4.  Results of CGAM's research are fed into Government machinery indirectly through its contribution to the research objectives of the Hadley Centre for Climate Prediction and Research (which is supported by and reports to the DETR), and directly through specially commissioned assessment panels, eg the Stratospheric Ozone Review Group, sponsored by the DETR and the Met Office, which advises government on the effects of man-made pollution on the ozone layer. My experience is that UK scientists give Government a balanced view of the issue of global warming, based on the best science available. Alternative views are encouraged and debated when these views are expressed in terms of ideas that can, at least in principle, be tested by the scientific method. The message that there remain considerable uncertainties in our ability to predict climate accurately does not always stay in the front of people's minds. There is therefore the danger that any unexpected departure from predictions, which might be short-term, may lead to complete scepticism about the scientific basis for global warming and a relaxation of vigilance by society.

  5.  The Intergovernmental Panel for Climate Change has played an important role in focusing and co-ordinating climate research internationally, and helping to set the scientific agenda. IPCC reports are widely read outside the climate science community. It should play an increasingly prominent role in encouraging concerted, co-ordinated efforts to understand, portray and ultimately remedy, uncertainties and deficiencies in climate prediction models.

29 February 2000

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