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.
"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."
