Europe's 2003 Heatwave Altered Carbon Cycle, Study Says
LONDON Europe's devastating heat wave, which claimed 35,000 lives in 2003, also reduced plant growth across the continent by 30 percent and may have contributed to global warming, French researchers said on Wednesday.
Hotter temperatures are usually thought to enhance plant growth by prolonging the growing season.
They are also thought to slow the rate of climate change by increasing the amount of carbon dioxide (CO2) that vegetation and trees, so-called carbon sinks, absorb from the atmosphere.
But low rainfall in eastern Europe in 2003 and extremely hot temperatures in western Europe combined to reduce plant growth in a way that was unprecedented during the last century. It also lessened the amount of CO2 taken in by plant ecosystems.
"It stopped the CO2 uptake by plants and within a few weeks the plants started, in the middle of the summer, to emit CO2 into the atmosphere instead of their normal behaviour where they pump CO2 out of the atmosphere," Dr Philippe Ciais, a carbon cycle scientist at the Laboratory of Climate and Environmental Sciences in Gif sur Yvette, France, said in an interview.
He and his colleagues used computer models and studied records of crop yields, satellite photographs of plant cover and observations of CO2 taken up by ecosystems. Their findings are reported in the science journal Nature.
The scientists warned that future droughts and severe temperatures could turn ecosystems in temperate climates into carbon sources by damaging the ability of plants to absorb CO2 from the atmosphere.
"Extreme events such as the 2003 European drought and heat wave have the potential to significantly alter long-term continental carbon balances," Ciais and his colleagues warned in the Nature report.
Dennis Baldocchi of the University of California at Berkeley said the findings could have an impact on the Kyoto Protocol on climate change.
"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 sinks," he explained in a commentary in the journal.
The 1997 Kyoto protocol is aimed at stopping climate change by reducing the amount of greenhouse gases such as carbon dioxide released into the atmosphere by industry.
Greenhouse gases trap heat in the Earth's atmosphere.
Kyoto calls for cuts in emissions by 5.2 percent below 1990 levels by 2008-