2003 heatwave 'may have sped up global warming'
Wednesday, 21st September 2005, 17:47
LIFE STYLE EXTRA (UK) - The record heatwave that scorched Europe two
years ago killing tens of thousands of people could have led to a
devastating increase in global warming, new research shows.
Soaring temperatures meant not only were crop yields lower than
normal, but the European ecosystems became a source of climate
change, because less vegetation meant a reduction in the amount of
carbon dioxide absorbed from the atmosphere.
The summer of 2003 produced the hottest August on record in the
northern hemisphere, unleashing massive forest fires and claiming an
estimated 35,000 lives.
Now French researchers have calculated that plant growth across the
continent was reduced by about 30 per cent.
Climate models have generally tended to predict global warming will
enhance plants and prolong the growing season - raising the amount of
carbon fixed in plant tissues. But the 2003 heatwave had the opposite
effect, according to the findings published in Nature.
Low rainfall in eastern Europe and extreme temperatures in western
Europe, which topped 40 degrees centigrade in France, for example,
combined to hinder plant growth in a way that was unprecedented over
the past century.
The researchers at the Laboratory for Climate Sciences and the
Environment at Gif sur Yvette analysed computer models of the
interactions between climate and the biosphere, and combined them
with observations of carbon dioxide uptake from ecosystems, and
records of crop yields.
Dr Philippe Ciais, who led the research, warned the findings may be
indicative of a future pattern in which droughts transform ecosystems
from carbon sinks to carbon sources - accelerating climate change.
Dr Ciais said: "Our results suggest that productivity reduction in
eastern and western Europe can be explained by rainfall deficit and
extreme summer heat, respectively. We also find that ecosystem
respiration decreased together with gross primary productivity,
rather than accelerating with the temperature rise.
"Model results, corroborated by historical records of crop yields,
suggest that such a reduction in Europe's primary productivity is
unprecedented during the last century.
"An increase in future drought events could turn temperate ecosystems
into carbon sources, contributing to positive carbon-climate
feedbacks already anticipated in the tropics and at high latitudes."
He said that extreme events such as the 2003 European drought and
heatwave have the potential to significantly alter long-term
continental carbon balances.
Dr Ciais added: "In Europe, more frequent extreme drought events may
counteract the effects of the anticipated average warming and
lengthening of the growing season, and erode the health and
productivity of ecosystems, reversing sinks to sources, and
contributing to positive carbon-climate feedbacks.
"This study only attempts to quantify the short term consequences of
extreme climate conditions on productivity, but the long term impacts
are likely to be significant as well."
Environmental scientist Dennis Baldocchi, of the University of
California, said the summer of 2003 in Europe is a particular case
worth studying because rainfall fell 50% below the long term norm.
More notably, average air temperatures exceeded the average since
1851 by more than 6 degrees centigrade.
Professor Baldocchi said: "According to data derived from the timing
of the grape harvest in Burgundy, this heat spell has had no equal
Prof Baldocchi said the report shows how episodes of heat and drought
will affect the ability of European countries to comply with the
requirements of the Kyoto Protocol to reduce carbon emissions by
limiting fossil fuel combustion or increasing terrestrial carbon
He added: "One potential outcome would be the production of real time
information on carbon cycling, so that fossil fuel combustion could
be adjusted as the weather changes.
"Achieving such a goal, however, would require an integrated
modelling system that predicts weather and carbon cycling in tandem,
and the expansion of satellite and field measurement systems that
would feed such a model."
Scientists fear deaths from heatwaves are likely to increase in the
decades ahead. France suffered the worst losses in August 2003, with
14,802 people dying from causes attributable to the blistering heat,
more than 19 times the death toll from the SARS epidemic worldwide.
The searing August heat claimed about 7,000 lives in Germany, almost
4,200 lives in both Spain and Italy. More than 2,000 people died in
the UK, with the country recording its first ever temperature over
100 degrees Fahrenheit on 10th August.
By the end of this century, the average world temperature is
projected to climb by 1.4 to 5.8°C. Over the past 25 years, the
average global temperature has risen by 0.6 degrees centigrade.
Heatwaves are a silent killer, mostly affecting the elderly, the very
young, or the chronically ill.