Brussels
TROPICAL farmers may be bigger polluters than the motorists of Europe and
North America, according to Nobel laureate Paul Crutzen. But no one is making
the measurements to find out.
Ozone smogs over rural Brazil, central Africa and Borneo are often worse than
in the smoky capitals of Europe, Crutzen told a conference on climate and ozone
in Brussels this week. During the southern dry season, emissions of carbon
monoxide are greater in the southern hemisphere than in the northern hemisphere.
鈥淵ou might think there鈥檚 not much pollution in the tropics, but you鈥檇 be wrong,鈥�
he said.
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The chief culprit is the burning of biomass, said Crutzen, who works at the
Max Planck Institute for Chemistry in Mainz. He shared last year鈥檚 chemistry
Nobel prize for explaining the reactions responsible for destroying the ozone
layer.
Forest fires started by farmers in the Brazilian Amazon and on the islands of
Borneo and Sumatra sent thick smoke thousands of kilometres in several recent
years. But according to Crutzen, burning forest accounts for only a small part
of the vegetation that goes up in smoke each year in the tropics.
Other contributors are deliberate fires in savanna grasslands, burning farm
wastes and slash-and-burn agriculture. In total, burning vegetation in the
tropics releases between 1.8 and 4.7 billion tonnes of carbon a year (
see
Table). The main products of these tropical fires are carbon monoxide, methane,
nitrogen oxides and carbon dioxide. One by-product of these emissions is ozone.
In the dry season in the Brazilian grassland region of Matto Grosso, ozone
concentrations at Cuiab谩 reach 90 parts per billion. In Europe鈥檚
capitals, this would be enough to trigger smog alerts.FIG-20300301.jpg
Crutzen warned that there was an urgent need for more monitoring of the
tropical atmosphere. And he said the concentration of international research in
climate and atmospheric chemistry in a handful of industrialised countries was
鈥渕ost unfortunate, a ridiculous situation鈥�. Failure to involve Third World
scientists in this research could undermine future climate treaties.
At present, he said, 鈥渨e don鈥檛 even have simple atmospheric measurements for
much of the tropics. Yet this is where the big future changes in atmospheric
chemistry will take place, as tropical countries industrialise.鈥�
The meeting was called by officials from the European Commission鈥檚
environmental research programme, who were worried that Crutzen and other
European luminaries in the field could lose out in a current reappraisal of the
Commission鈥檚 research budget. But Crutzen said the money should be spent not in
Europe but on long-term research in the tropics.
Such research, he argued, could ultimately rewrite the textbooks. 鈥淲e can鈥檛
assume that emissions in the tropics will behave in the same way as in
mid-latitudes.鈥� The particle chemistry of emissions from coal burning in the
hot, dusty air of India, for instance, could be very different from that in
Europe, he said.
The saving grace for the tropical atmosphere could be that the region is also
the heart of the planet鈥檚 atmospheric cleansing processes. These processes are
centred on the hydroxyl radical (OH), an unstable and rare compound, which is
created when ultraviolet radiation bombards ozone and the products react with
water vapour. Many pollutants, such as carbon monoxide and methane, are
destroyed by reactions with OH that take place largely in the tropics, where the
intense solar radiation produces a higher concentration of OH radicals.
The conference discussed several oddities of the global atmosphere that could
bring surprises. Why, for example, Crutzen asked, is there virtually no ozone in
the upper troposphere over much of the Pacific Ocean? 鈥淭here seem to be ozone
destruction processes that we don鈥檛 yet know about,鈥� he said.
The conference also heard from climate researchers who are finding intriguing
patterns in the weather that could help long-term forecasting. El
Ni帽o鈥攖he periodic reversal of winds and waves in the tropical
Pacific鈥攕eems to cause the failures of the Asian monsoon. With El
Ni帽o now usually predictable up to a year ahead, scientists are close to
offering monsoon forecasts that 鈥渃ould help three-fifths of the world鈥檚
population鈥�, said Hartmut Grassl, of the World Climate Research Programme in
Geneva.
Researchers have uncovered a 15-year cycle in temperatures in the North
Atlantic鈥攁pparently caused by subtropical gyres, giant circular water
movements, flinging warm water north, said Grassl. Within 20 years, it might be
possible to use this to predict hot European summers. That could come in handy
if there were ever a repetition of events 11 500 years ago, at the end of the
last ice age, when Britain鈥檚 average temperature warmed by 10 掳C in less
than a lifetime.