Å®ÉúСÊÓƵ

Western Europe could face higher temperatures in the next few years
as governments clean up acid rain, according to scientists at Britain’s
Meteorological Office.

Global warming, evident over most of the rest of the planet in the past
decade, has so far been ‘slow or absent’ over the northwest Atlantic and
Western Europe, according to the conclusions of a revised assessment by
the UN’s Intergovernmental Panel on Climate Change (IPCC) released last
week. A prime reason has been the shielding from the Sun’s heat provided
by sulphur emissions from power stations, one of the main sources of acid
rain.

‘The implication must be that, as countries clean up sulphur emissions
to halt the damage from acid rain, temperatures will rise,’ says Bruce Callander
of the Meteorological Office, a leading member of the IPCC working group
on the science of climate change.

Research published last year revealed for the first time that in parts
of the northern hemisphere the shading effect of sulphate aerosols in the
atmosphere is sufficient to offset much of the impact of global warming,
which is caused by the accumulation of other pollutants, mainly carbon dioxide
(This Week, 4 January).

Callander said this week that the impact of sulphate aerosols could
explain why temperatures in the northern hemisphere generally have increased
less than those in the south. The IPCC adds that when the cooling effect
of sulphate aerosols and the depletion of stratospheric ozone are included
in the models, they provide a better fit between predicted global temperature
changes over the past century and actual observations.

The political impact of the IPCC report is double-edged. While strengthening
the scientists’ confidence in their models of climate warming, it has led
to headlines such as that in the Financial Times last Saturday, which claimed:
‘Pace of global warming may be less than thought’.

These reports may reduce the pressure on the US to agree limits to its
emissions of carbon dioxide during discussions on a treaty on global climate
change, which resume in New York next month.

This would be doubly ironic because the IPCC report also undermines
what was until recently a central plank of the US case against taking action.
The US argued that its efforts to phase out emissions of CFCs would reduce
by around 20 per cent the American contribution to global warming. CFCs,
which are being phased out worldwide to protect the thinning ozone layer,
are also strong greenhouse gases.

But new research by American atmospheric chemists, published last year
(This week, 9 November 1991) and endorsed by the IPCC last week, has shown
that the thinning of the ozone layer has a cooling effect that has now entirely
offset the warming effect of the CFCs. So reducing CFCs will have little
effect on global warming.

The IPCC report also slightly diminishes the role in global warming
of methane, often regarded as the second most important greenhouse gas after
carbon dioxide. It finds that ‘rates of increase in the atmospheric concentrations
of methane have slowed’ and ‘some data indicate lower emissions of methane
from rice paddies than previously estimated’. These findings again underline
the primacy of carbon dioxide emissions, largely from the industrialised
nations, in global warming.