December 7, 2009 – Original Source: Telegraph, UK
The Earth may be 50 per cent more sensitive to the warming effect of carbon dioxide greenhouse gas than has previously been thought, scientists claim.
A new study suggests bigger cuts in carbon dioxide (CO2) emissions may be needed to prevent drastic long term climate change.
The evidence was obtained by scientists looking back three million years to the Pliocene epoch, when global temperatures were 5.4F (3C) to 9F (5C) higher than they are today.
They found that levels of CO2 in the atmosphere at the time should not have produced such a warm world.
Climate models used to predict modern levels of man-made global warming, temperatures in the mid-Pliocene should have been lower.
The findings suggest the Earth’s temperature may be 30 per cent to 50 per cent more sensitive to atmospheric carbon dioxide than experts have assumed.
The discrepancy can be explained by long term changes in vegetation and ice cover.
Ice reflects solar radiation back into space and therefore helps to prevent the Earth heating up. When ice melts and disappears this “albedo” effect is lessened, contributing to a rise in temperature.
Vegetation absorbs carbon dioxide but also keeps the Earth warm by preventing heat reflection.
The scientists compared temperature reconstructions from sediments in the ocean floor with a global climate simulation model which aimed to map climate three million years ago.
Study leader Dr Dan Lunt, from the University of Bristol, said: “We found that, given the concentrations of carbon dioxide prevailing three million years ago, the model originally predicted a significantly smaller temperature increase than that indicated by the reconstructions. This led us to review what was missing from the model.”
They believe current models do not accurately represent the sensitivity of global temperatures to CO2.
Climate models used by bodies such as the Intergovernmental Panel on Climate Change often fail to take full account of such effects, said the researchers, whose findings are reported in the journal Nature Geoscience.
“If we want to avoid dangerous climate change, this high sensitivity of the Earth to carbon dioxide should be taken into account when defining targets for the long-term stabilisation of atmospheric greenhouse gas concentrations,” said Dr Alan Haywood, the co-author from the University of Leeds.
Although the Pliocene marked the transition to a cooler global climate, it went through a warm spell of around 300,000 years when temperatures were significantly higher than they are today.
The first recognisable ancestors of modern humans evolved during the Pliocene epoch.
Meanwhile, a new documentary shows that global warming was not always a bad thing as it once saved early man from extinction.
Man On Earth, a Channel Four documentary starting today claims that without the last great global warming 120,000 years ago our ancesters would have died out.
Instead as the temperatures increased by as much as 9F (5C) in less than 200 years, man flourished and began to spread across the globe.
The programme, presented by Tony Robinson, charts the progress of early homo sapiens in Ethiopia 160,000 years ago during a great ice age.
The temperatures were so cold that our ancestors survived only in small patches in Africa and at one point numbered only 10,000. Most of the Earth was covered in ice with the rest vast deserts stretching thousands of miles. The only oasis of life was in the highlands of Ethiopia.
Then around 120,000 years ago, the Earth started to warm during a periods known as the Eemian period and this brought life and abundance to Africa.
Man flourished and from beginnings in Africa, spread to the Middle East and then Europe.
“It is hard to overstate the impact of climate change on our earliest ancesters,” Robinson explains.
“The ice age had nearly destroyed them. Global warming had rescued them from the brink of destruction and cemebted their position as one of the most powerful species in Africa.”
The population expanded rapidly from 10,000 to 100,000 within a few hundred years.