Global warming -- more caused by human activity

NEW YORK: A study by a team of scientists led by NASA climatologist James Hansen has found that the unusual magnitude of the global warming trend experienced could not be explained by natural is responsible.

Hansen and his team of 14, all from NASA, Columbia and the Department of Energy, had co-authored the study reported in the journal Science.

Hansen's team said global temperatures will rise 1 degree Fahrenheit this century even if greenhouse gases are capped tomorrow.

However, if carbon dioxide and other heat-trapping emissions instead continue to grow, as expected, things could spin "out of our control," especially as ocean levels rise from melting Greenland and Antarctic ice sheets.

Experts predict a 10-degree leap in Fahrenheit readings in such a scenario.

The researchers measured Earth's energy imbalance because of more precise ocean readings collected by 1,800 technology-packed floats deployed in seas worldwide beginning in 2000, in an international monitoring effort called Argo. The robots regularly dive as much as a mile undersea to take temperature and other readings. They found that for every square meter of surface area, the planet is absorbing almost one watt more of the sun's energy than it is radiating back to space as heat. This absorbed energy will steadily warm the atmosphere.

The new temperature readings from the deep ocean trace a clear warming trend that seems impossible to turn around any time soon.

Hansen said in a summary of the report: "This energy imbalance is the 'smoking gun' that we have been looking for. The magnitude of the imbalance agrees with what we calculated using known climate forcing agents, which are dominated by increasing human-made greenhouse gases. There can no longer be substantial doubt that human-made gases are the cause of most observed warming."

Hansen, director of NASA's Goddard Institute for Space Studies at the Columbia University Earth Institute, said the delayed consequences of past or current greenhouse gas emissions is due to the "thermal inertia" of the planet, an effect most noticeable at the ocean's edge when the morning sun begins to warm sand while the water remains seemingly unaffected. It takes more of the sunlight's energy to penetrate into the water, particularly at its lowest depths, than it takes to warm a shallow bit of land.

Scientists still debate how serious the problem is and what could be the antidotes. The Bush administration has resisted request to limit greenhouse gas emissions saying more research is needed.

Hansen confirmed that global warming is real, and scientists are now able to calculate within an acceptable range of uncertainty how much the planet's retained energy balance is increasing. By their reckoning, the "net forcing" works out to mean that about 0.85 watts per square meter is being retained by the Earth -- a seemingly tiny amount compared to the nearly 250 watts per square meter coming in from the Sun.

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