Heatwave study raises new global warming fear
Financial Times, Sept. 22 2005
The finding, based upon an examination of the effects of the 2003 heatwave in Europe, is of particular concern because many scientists previously assumed that global warming would increase plant growth, with beneficial effects for harvests and the environment.
In a study to be published on Thursday in the peer-review journal Nature, scientists from several European research institutes and universities found that the growth of plants during the heatwave was reduced by nearly a third.
In Italy, the growth of maize dropped by about 36 per cent. Oak and pine also grew much less, the study found, reflecting an overall reduction of 30 per cent in plant growth. Wheat crops, however, were less affected because of the timing of the heatwave and the accompanying drought, which saw mean air temperatures rise by as much as 6° Celsius above their long-term average and rainfall at half of the long-term norm.
Climatologists say climate change will bring an increase in the frequency of heatwaves.
Apart from the effects on the harvest, the decline in the productivity of plants spells bad news for the environment as a whole.
Greater plant growth means that plants are removing more carbon dioxide from the atmosphere. This would lessen global warming over time, because the climate is believed to be changing under the influence of a surfeit of carbon dioxide, a gas that traps heat in the earth's atmosphere. Human activity has caused this increase in the gas, which is produced when fossil fuels are burned.
The heatwave study follows experimental results from the US that show plants do not grow faster when there is more carbon dioxide in the atmosphere. Previous models of climate change had assumed a doubly beneficial effect from plants growing faster under warmer conditions, while there was more carbon dioxide available. If plants grow less during heatwaves, and fail to grow faster when there is more carbon dioxide present, scientists will have to revise their predictions of the likely severity of the effects of climate change.
In another recent study, scientists at Cranfield University found that an unexpectedly large amount of carbon dioxide was released from the soil under warming conditions. This could raise the amount of carbon dioxide in the atmosphere, which many governments have been attempting to reduce.
Killer heatwave may have fuelled global warming
The Guardian (U.K.), Sept. 22, 2005
Europe's great heatwave of 2003, which claimed an estimated 35,000 lives and cost the continent's economies an estimated £7bn altogether, may also have fuelled further global warming. A team of more than 30 scientists reports in Nature today that the scorching temperatures and prolonged drought have stifled Europe's forest growth and released huge quantities of carbon dioxide into the atmosphere, to feed still warmer summers in future.
Philippe Ciais from the Laboratory for Climate Sciences and the Environment at Gif-sur-Yvette, France and colleagues from Germany, Italy, Switzerland, Belgium, Spain, Finland and Portugal, took a snapshot of plant life across Europe using satellite data to measure the sunlight being absorbed by beech woodland and pine and oak forests, as well as grassland and stands of spruce.
They measured crop yields and the rate of plant growth to construct a picture of how much carbon was absorbed from the atmosphere, and how much returned.
In temperate climates, forests act as a carbon "sink", with some of the greenhouse gases released from fossil fuels becoming locked away again as wood, leaf litter and buried vegetation. But the picture in the summer of 2003 was dramatically different. Plant growth in Europe dropped that summer by 30% overall, and much of the carbon dioxide removed from the atmosphere in the previous four years was released again.
"Such a reduction in Europe's primary productivity is unprecedented during the last century," the scientists report. "An increase in future drought events could turn temperate ecosystems into carbon sources, contributing to positive carbon dioxide feedbacks already anticipated in the tropics and high latitudes."
This is the third warning in three weeks that global warming could be moving to a point of no return. A week ago, US scientists calculated that hurricanes categorised as the most violent had almost doubled in frequency over the past 35 years as sea surface temperatures rose. Two weeks ago a Cranfield University team, who sampled topsoil at 6,000 places in England and Wales over 25 years, reported in Nature that England's soils were sending back carbon to the atmosphere at the rate of 4m tonnes a year. The latest news dashes the hope, nursed by climate scientists, that the mix of longer growing seasons and greater levels of carbon dioxide would "fertilise" more vigorous plant growth and offset some of the discharges from factory chimneys and car exhausts.
Climate scientists have already warned that heatwaves of the kind that parched vineyards, ruined orchards, damaged harvests, set forests blazing and claimed so many lives in 2003 that mortuaries overflowed could become more frequent. No one can guess quite how the trees will react as the temperature rises.
"It is reasonable to expect that forests will acclimate if mean temperatures continue to rise gradually across Europe," Dennis Baldocchi, of the University of California, Berkeley, writes, also in Nature. "A repeat of extreme temperatures in the near term, on the other hand, could have detrimental, even lethal consequences."
Europe's 2003 Heat Wave Altered Carbon Cycle
Planetark.org, Sept. 22, 2005
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 2008-12.