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MARIN COUNTY'S NEWS MONTHLY - FREE PRESS
(415)868-1600 - (415)868-0502(fax) - P.O. Box 31, Bolinas, CA, 94924

May, 2005

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Earth Absorbing More Heat Than It Radiates
By Fred Pearce

The Earth is absorbing more energy from the Sun than it is emitting to space, according to a new modelling study. The difference amounts to 0.85 watts for every square metre of the planet's surface. That is equivalent of 7 trillion 60-watt light bulbs - or the energy output of almost half a million thousand-megawatt power stations.
Most of the extra heat is warming the oceans - the ultimate repository of most of the solar radiation reaching the Earth, says Jim Hansen, director of NASA's Goddard Institute for Space Studies in New York, US, and a leading climate change scientist for the past two decades.
The findings are the result of modelling studies of the atmosphere's "energy budget" by a US team, headed by Hansen. The calculations are supported by precise measurements of ocean temperature over the past 10 years, he says.
The conclusion provides evidence both of planetary warming and of the lag in the response of the planet to the warming created by the accumulation of greenhouse gases in the atmosphere - gases which trap infrared heat, preventing it from dissipating into space.
Hansen calculates there is currently 0.6íC of warming already "in the pipeline". This is as much again as the warming actually experienced over the past century. Half of it is likely to be manifested in the next 30 to 40 years, with the rest over succeeding decades, he says.
The time lag occurs because it takes decades to warm the oceans - a process that happens gradually through mixing colder deep waters with the warmed surface waters.
Iceberg Armada
Hansen says the lag represents a ticking time-bomb: "If we wait for more overwhelming empirical evidence of climate change [before acting], still greater climate change will be in store," he says. But it also provides an advantage. If we act now to halt climate change, he says, it gives the world time to head off the worst predicted consequences.
Climate sceptics will not be convinced. Richard Lindzen, a meteorologist at Massachusetts Institute of Technology, US, says: "Frankly, we can't measure such [thermal] imbalances. So the results must be based on suppositions."
But Peter Cox of Britain's Centre for Ecology and Hydrology in Dorset, UK, says the calculation of the energy imbalance should help scientists gauge the sensitivity of the climate system to the "forcing" effect of greenhouse gases. In other words, how much warming we can expect from a given increase in concentrations of the gases.
And this could be critical for staving off dangerous climate change. In a recent paper in Climatic Change (v 68, p 269), Hansen argues that any warming in excess of 1íC - measured from today - could trigger runaway melting of the world's ice sheets. The process might start with Greenland unleashing "vast armadas of icebergs" into the oceans and sea levels rising by many metres, he said.
If his new assessment is correct, the Earth is already well on the way to having that amount of warming "in the pipeline".
NewScientist.com news service, Journal reference: Science (DOI: 10.1126/science.1110252)

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