Energy Imbalance Behind Global Warming

Climate change has been looked at from many angles. Here's another twist: Scientists have determined that more energy is being absorbed from the Sun than our planet reflects back to space.

This energy imbalance, the researchers said today, confirms other predictions that Earth's climate will warm by about 1 degree Fahrenheit (0.6 Celsius) by the end of this century.

The study is based on satellite data and computer models. It precisely measured ocean heat content over the past decade. The imbalance is due to increased air pollution, especially carbon dioxide and other greenhouse gases that act like a see-through blanket, letting sunlit in but trapping the heat it generates.

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1-watt light bulb

In scientific terms, the imbalance is 0.85 watts per square meter. It's equal to nature shining an extra 1-watt light bulb on every desk-sized patch of the planet.

It all adds up. If the imbalance were maintained for 10,000 years, it would melt enough ice to raise the oceans by six-tenths of a mile (1 kilometer), the scientists said.

The analysis lends support to the contentious idea that humans are contributing to the warming trend by burning gas, coal and other fossil fuels that generate greenhouse gases.

"This energy imbalance is the 'smoking gun' that we have been looking for," said lead researcher James Hansen, director of NASA's Goddard Institute for Space Studies, part of the Earth Institute at Columbia University. "It shows that our estimates of the human-made and natural climate forcing agents are about right, and they are driving the Earth toward a warmer climate."

The study is detailed in the online version of the journal Science.

Inevitable change?

Though some scientists challenge the idea that humans contribute to global warming, few dispute that the planet is getting warmer. A study earlier this year confirmed that last year was among the four warmest on record and projected 2005 will be the warmest.

Previous computer modeling has estimated that the global climate will warm for at least the next century, and likely longer, no matter what changes might occur today -- even if production of greenhouse gases stopped. That's because the ocean stores heat and changes slowly, a process scientists call thermal inertia.

Future warming is already "in the pipeline," as Hansen and his colleagues put it.

The previous work concluded that the seas will rise at least 4 inches (10 centimeters) this century, posing increased risks to coastal regions around the globe.

Hansen and his colleagues say that if pollution is not curbed until policy makers decide they have proof of human input, "thermal inertia implies that still greater climate change will be in store, which may be difficult or impossible to avoid."

"Warmer waters increase the likelihood of accelerated ice sheet disintegration and sea level rise during this century," Hansen said.

Since 1993, data from satellite altimeters, used to measure sea level, have shown that the world's oceans have risen by 3.2 centimeters (cm), or 1.26 inches, per decade (plus or minus 0.4 cm).

That's twice as large as sea level rise in the last century.

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