Earth's Greenhouse Gas
Build-Up Worst In 20
Million Years
Tim Radford - Science Editor,3604,355070,00.html
The two men analysed the shells of tiny ocean creatures to build up a fossil record of the chemistry of the atmosphere for the past 60m years. Their discovery will add to pressure on governments to implement international agreements to reduce the greenhouse gases that fuel global warming. The news comes hard on a report from the University of Colorado that Arctic temperatures are at their warmest for at least 400 years.
Paul Pearson of the University of Bristol and Martin Palmer of Imperial College, London, report in Nature today that they used the evidence of plankton shells drilled from the seabed to estimate the acidity of the sea water over a span of time back almost to the era of the dinosaurs. Carbon dioxide dissolves in water to form a weak carbonic acid. They reasoned that the tissue of floating organisms would reflect the carbon dioxide levels of the world around them - and then hold that record locked in the fossilised shells.
Other studies of more recent records have confirmed a picture of a rapid warming in the past two decades. Winter is in retreat. The growing season in Europe is 11 days longer than it was 35 years ago. Sea levels have crept higher throughout the century. Six of the 10 warmest years ever recorded occurred in the 1990s; the other four all happened in the late 1980s. The Arctic ice cover is in retreat, shrinking by an area the size of the Netherlands every year. It is also thinning, from more than three metres thick to less than two metres in 30 years.
Now a team from Boulder, Colorado, reports this week in the Dutch journal Climate Change that wherever it looked - at Arctic ice cores, lake sediments or plant growth in the permafrost - it saw confirmation that the Arctic had warmed by 6C in the past 30 years.
But in the tropics, humans have felt the impact more cruelly. Researchers long ago predicted more storms, droughts and floods as a consequence of a warmer world, and both the economic costs, and the numbers of victims of climate-related disasters, have increased in the past decade.
Paul Epstein, of the Harvard medical school in the US, warns in this month's Scientific American that global warming must also mean an increase in water-borne and insect-borne diseases to add to the threat.
But until now researchers have had no clear idea of the long term pattern of the planet's atmosphere. Dr Pearson said: "Our observations put the modern greenhouse effect into a long term perspective."
For much of the past 20m years, the planet has been quite cool. An Australian team reports in Nature today that at the height of the last ice age, 21,000 years ago, sea levels were 135 metres lower than today, and the continents were covered by an extra 52m cubic kilometres of ice.
But carbon dioxide levels are rising swiftly because of fossil fuel burning and the clearing of the planet's forests, which in past aeons have taken carbon from the air and stored it, first as wood and then as coal. By 2100 the carbon dioxide levels will increase to match those last seen in the Eocene, 50m years ago. In those days, much of Europe was flooded, there were no ice caps, London was a steaming mangrove swamp and the average temperature of southern England was 25C. Today, the average temperature is 10C.
Professor Palmer said: "This does not necessarily mean we will recreate Eocene-type conditions. There are still too many unknowns involved in climate prediction. But the sweltering ice- free world of the Eocene does warn us of what might happen if a runaway greenhouse effect sets in."
Useful links < of Concerned Scientists < Framework Convention on Climate Change < of East Anglia's Climatic Research Unit

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