Using ocean data collected by diving floats, U.S. climate scientists released a study Thursday that they said provides the "smoking gun" that ties manmade greenhouse gas emissions to global warming.
The researchers, some of them working for NASA and the Energy Department, went a step further, implicitly criticizing President Bush for not taking stronger action to curb emissions of carbon dioxide and other heat-trapping gases.
They said the findings confirm that computer models of climate change are on target and that global temperatures will rise 1 degree Fahrenheit this century, even if greenhouse gases are capped tomorrow.
If 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, the NASA-led scientists said. "The climate system could reach a point where large sea level change is practically impossible to avoid."
The study, published Thursday in the journal Science, is the latest to report growing certainty about global warming projections.
Floats and satellites used
More than 1,800 technology-packed floats, deployed in oceans worldwide beginning in 2000, are regularly diving as much as a mile undersea to take temperature and other readings. Their precise measurements are supplemented by better satellite gauging of ocean levels, which rise both from meltwater and as the sea warms and expands.
Researchers led by NASA’s James Hansen used the improved data to calculate the oceans’ heat content and the global “energy imbalance.” 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 — a historically large imbalance. Such absorbed energy will steadily warm the atmosphere.
The 0.85-watt figure corresponds well with the energy imbalance predicted by the researchers’ modeling of climate change through a supercomputer, the report said.
Computer models, which are numerical simulations of climate change, factor in many influences on climate, including greenhouse emissions. Such gases, produced naturally but also by humans burning fossil fuels, trap heat as they accumulate in the atmosphere.
'Can no longer be genuine doubt'
Significantly, those emissions have increased at a rate consistent with the detected energy imbalance, the researchers said.
“There can no longer be genuine doubt that humanmade gases are the dominant cause of observed warming,” said Hansen, director of NASA’s Goddard Institute for Space Studies. “This energy imbalance is the ‘smoking gun’ that we have been looking for.”
Fourteen other specialists from NASA, Columbia University and the Department of Energy co-authored the study.
Scientists have found other possible “smoking guns” on global warming in recent years, but Klaus Hasselmann, a leading German climatologist, praised the new report for its innovative work on energy imbalance. “This is valuable additional supporting evidence” of manmade climate change, he told The Associated Press.
Similar correlation in separate study
In February, scientists at San Diego’s Scripps Institution of Oceanography said their research — not yet published — also showed a close correlation between climate models and the observed temperatures of oceans, further defusing skeptics’ past criticism of uncertainties in modeling.
Average atmospheric temperatures rose about 1 degree Fahrenheit in the 20th century, and the Intergovernmental Panel on Climate Change, a U.N.-organized network of scientists, says computer modeling shows they will rise between 2.5 degrees and 10.4 degrees Fahrenheit by the year 2100, depending on how well emissions are controlled.
The Science study said the excess energy stored in the oceans means a 1-degree Fahrenheit rise in atmospheric temperatures is already “in the pipeline.” This agrees with findings of U.S. government climate modelers reported last month.
Besides raising ocean levels, global warming is expected to intensify storms, spread disease to new areas, and shift climate zones hundreds of miles, possibly making farmlands drier and deserts wetter.
The researchers also pointed out that the Earth has significant "thermal inertia," which delays changes to the planet's energy balance. And they used that point to urge policymakers to take action.
"This delay provides an opportunity to reduce the magnitude" of climate change "if appropriate action is taken," they wrote in the study. "On the other hand, if we wait for more overwhelming empirical evidence of climate change, the inertia implies that still greater climate change will be in store, which may be difficult or impossible to avoid."
President Bush has said that while he believes manmade emissions are tied to global warming, it's not known just how closely and that therefore drastic steps like mandatory emission curbs are unwarranted.
"We do not know how much effect natural fluctuations in climate may have had on warming," he said in a major climate policy speech in 2001. "We do not know how much our climate could, or will change in the future. We do not know how fast change will occur, or even how some of our actions could impact it."
"No one can say with any certainty what constitutes a dangerous level of warming," he added, "and therefore what level must be avoided."
The administration instead is relying on technology improvements and voluntary steps to reduce emissions over time.