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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