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Tuesday, 12 February, 2002, 18:23 GMT
Warming world 'means longer days'
Sunrise over Mount Fuji   AP
Blink and you will miss the extra microseconds
Alex Kirby

Belgian scientists have identified a hitherto unsuspected benefit of global warming - more time for all of us.

They say increasing levels of carbon dioxide (CO2) in the atmosphere will slow the Earth's rotation.

This will make every day a little longer than it is already.

But for the next century the increase will be so small that if you blink, you'll miss it.

The scientists, from Belgium's Royal Observatory and the Catholic University of Louvain, report their work in this month's issue of the journal Geophysical Research Letters.

They used computer models to analyse the effect of adding 1% more CO2 to the atmosphere annually.

This would mean a doubling of the CO2 concentration after 70 years. The researchers say this rate of increase is a common scenario on the basis of current human activity.

Elastic days

Science can already measure the length of the day to an accuracy of about 10 microseconds (one microsecond is one millionth of a second).

The length fluctuates slightly, because of changes in atmospheric winds and ocean currents, which affect the Earth's angular momentum as it spins on its axis.

Wind turbines against sun   1999 EyeWire, Inc.
Warmer and longer days lie ahead
Angular momentum measures the rotation of a non-rigid body, like a planet, including its ability to go on spinning.

The Belgian team estimated the effect of the ocean and atmosphere in a warming world on the Earth's angular momentum.

They found that each day would lengthen because of angular momentum changes, including variations in surface pressure over land masses, average surface pressure over the ocean, and zonal winds and currents.

The actual amount of lengthening would be small - microseconds per year.

In any given year it would be difficult to distinguish from naturally occurring variation.

Time expands

But over longer periods, the scientists say, the effect would be measurable, with a probable increase of 11 microseconds per decade during this century.

That would mean an increase of 11 hundred-thousandths of a second over the entire century.

One of the team, Dr Olivier de Viron, told BBC News Online: "When you increase the amount of CO2, you perturb the atmosphere's dynamics, the winds and so on.

"We know that globally the wind blowing from West to East will increase, so the Earth's rotation will decrease.

"The days will be longer - and the nights won't be shorter to compensate.

"It means 24 hours won't be 24 hours any more. It will be something a little bit more."

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