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Scientists Find Climate Change ‘Smoking Gun’

Times Staff Writer

The Earth is now absorbing so much heat from the sun that the soot and greenhouse gases that humans are putting in the air appear to be the only reasonable explanation for the warming trend, according to research released Thursday by a team of prominent climate scientists.

The scientists from NASA, Columbia University and the U.S. Department of Energy determined that precise, deep-ocean measurements showed a rise in temperature that matched their computer model predictions of what would happen in an increasingly polluted world.

The scientists wrote that the findings confirmed the planet’s “energy imbalance,” a long-held theory on global warming.

“This energy imbalance is the ‘smoking gun’ that we have been looking for,” said James Hansen, the director of NASA’s Goddard Institute for Space Studies at the Columbia University Earth Institute, and lead author of the study, published online Thursday by Science magazine.

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“There can no longer be substantial doubt that human-made gases are the cause of most observed warming,” added Hansen, who has long advanced the idea that human beings have been contributing to global warming, and in recent years has criticized the Bush administration for failing to take aggressive action on the issue.

Although the planet is now soaking up more energy from sunlight than it is reflecting back to space in the form of heat radiation, much of the excess energy remains effectively hidden in the oceans, the study found.

Just as the sands on a beach warm faster than the waters offshore, oceans respond more slowly to temperature changes than land masses.

But the heat trapped in the oceans will eventually manifest itself, with significant consequences for the world’s climate, the scientists wrote.

As a result, the average global temperature, which has increased by about one degree Fahrenheit over the last century, will do so again over the next century, simply based on the heat stowed away in the oceans.

“The Hansen paper is important,” said F. Sherwood Rowland, a UC Irvine professor who received the 1995 Nobel Prize for chemistry for finding that pollution from aerosol sprays and coolants was eroding the ozone layer.

“If you have that much [heat] stored up in the oceans, that is about another degree Fahrenheit that is lagging there, and we just haven’t felt it yet.”

Michael Prather, another UC Irvine professor, said that though Hansen and others had stated for years that the oceans could be a repository for much of the heat generated by the greenhouse effect, the latest paper represented the most convincing evidence yet that it was happening.

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“I always believed Jim [Hansen] was right in the first place, but now I think he has proved it,” said Prather, the former editor of the Geophysical Research Letters journal.

“You now see the heat building up in the ocean and you have a limited range of options to explain it.”

In addition to increasing global temperatures, the warming could lead to an acceleration of the ice sheet disintegration taking place in parts of the polar regions, and even a rapid rise in sea levels, the authors concluded.

Sea levels have risen about 1 1/4 inches in the last decade, twice the rate of the preceding century, partly because the heat content of the oceans has caused the water to expand.

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Based on major climate shifts in the planet’s history, Hansen estimates that if temperatures increased beyond 1.8 degrees Fahrenheit over current levels, large-scale sea level increases could take place.

He argued that represents the threshold that human beings should strive not to exceed. Under the U.N. Framework Convention on Climate Change, countries around the world agreed in principle to avoid “dangerous anthropogenic interference” with the climate, though they never defined what that was.

Natural variables such as ocean circulation patterns could theoretically account for the high rate of heat storage in deep waters, the authors conceded. But they said that in such a scenario, cooler water would have been pushed to the surface of the oceans, and the measurements over the last decade showed surface temperatures warming.

By contrast, the researchers noted that the additional heat in the oceans corresponds closely with what their computer model predicted would take place due to increased emissions of carbon dioxide, methane, ozone and black carbon, making that the more likely cause.

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Hansen estimated that if humans could slash the current amount of carbon dioxide in the atmosphere in half, or eliminate potent methane emissions, the planet’s heat would fall back into equilibrium. But such reductions, he said, are unrealistic, and thus the world probably will become warmer.


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