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[b]Rapid rise in global warming is forecast[/b]
Lewis Smith, Environment Reporter
The oceans are losing the capacity to soak up rising man-made carbon emissions, which is increasing the rate of global warming by up to 30 per cent, scientists said yesterday.
Researchers have found that the Southern Ocean is absorbing an ever-decreasing proportion of carbon dioxide in the atmosphere. The excess carbon, which cannot be absorbed by the oceans, will remain in the atmosphere and accelerate global warming, they said.
The reduced ability to absorb carbon is thought to be a result of high winds acting on ocean currents bringing deeper waters that already contain high levels of carbon to the surface.
The higher winds are themselves believed to have been caused by climate change due to a combination of changes in the ozone layer and carbon emissions.
The scientists from countries including Britain, France and Germany, said their findings marked the first time that one of the world’s natural “carbon sinks” had been shown to be weakened by Man’s own actions.
Ian Totterdell, a climate modeller at the Met Office Hadley Centre, described the research as “an important piece of work”.
He said: “This is the first time we have been able to get convincing evidence that a change in the uptake of CO2 by the oceans is linked to climate change.
“It’s one of many feedbacks we didn’t expect to kick in until some way into the 21st century.”
While a reduction in absorption rates by carbon sinks has long been forecast, the discovery that the Southern Ocean is mopping up less of Man’s carbon emissions has come at least two decades earlier than expected.
The Southern Ocean is the world’s biggest marine carbon sink and accounts for 15 per cent of all the carbon taken out of the atmosphere. Temperatures are already predicted to rise by almost 1.5C (2.7F) by the middle of the century, without taking into account any further emissions caused, for example, by the rapid construction of fossil fuel power plants in China and India.
The weakening of the Southern Ocean’s absorption rates– which could be in the range of 5 to 30 per cent– is likely to result in an increase in the rate at which temperatures rise, scientists say.
“This is serious,” said Corinne Le Quéré, of the University of East Anglia (UEA) and the British Antarctic Survey (BAS), two of the world’s leading environmental research centres. “This is the first time that we’ve been able to say that climate change itself is responsible for the saturation of the Southern Ocean sink. “With the Southern Ocean reaching its saturation point more CO2 will stay in our atmosphere. Since the early 1980s the carbon sink hasn’t changed. In the same period the emissions have gone up by 43 per cent.”
Dr Le Quéré led a team measuring atmospheric carbon dioxide, which found that, despite this rise in emissions since 1981, the quantity absorbed by the ocean was static.
Since the industrial revolution an estimated 500 giga-tonnes of carbon dioxide has been released into the atmosphere through the use of fossil fuels, cement manufacture and changes in land use.
About a quarter of this has been absorbed by the oceans and a further quarter taken up by vegetation.
The research, published in Science, identified changes in wind patterns caused by climate change as being the direct cause of the weakened ability to absorb carbon dioxide.
While able to pinpoint the hole in the ozone layer and carbon emissions as the man-made causes of the increased winds, the researchers were unable to identify which of them had the greater effect.
The net quantity of carbon dioxide absorbed by the Southern Ocean remained at 0.3 billion tonnes a year from 1981 to 2004, according to calculations by the research team.
In 1981 it absorbed 0.6 billion tonnes from the atmosphere but emitted 0.3 billion tonnes back into it. In 2004 it absorbed 0.8 billion tonnes but emitted 0.5 billion tonnes. In the report they said that climate models project more intense Southern Ocean winds if CO2 levels continue to increase over the next century.
The researchers accepted there were limits to the data available from the Southern Ocean and that “the magnitude of the CO2 sink is heavily disputed”.
Professor Chris Rapley, director of BAS, said uncertaintities remained, but the findings were “a serious concern”.
He said the reduced efficiency of the ocean to act as a carbon sink would make it harder to reduce emissions to levels that were low enough to limit temperature rises to 2C.