An international team of scientists has taken another look at how rapidly Earth's atmosphere is absorbing carbon dioxide (CO2)--the biggest greenhouse gas in terms of volume--and the news is not good: A high-flying world economy is pumping out the gas at an unprecedented rate. Current CO2 production is outstripping the best estimates used by modelers to predict future climate trends.
Earth's climate has been warming for the past century or so, particularly during the past 40 years. Scientists say the blame most likely belongs to an increase in the greenhouse effect, caused by human output of CO2, methane, and types of fluorocarbons. The U.N. Intergovernmental Panel on Climate Change cites human activity as the biggest contributor to the phenomenon known as global warming.
During the past half-century, scientists have been closely monitoring the changes in the atmosphere and have constructed elaborate computer models to project what will happen if current trends in CO2 output continue. What's going on now in the real world is surpassing the assumptions of the climate models.
As the international team of 10 researchers writes online today in the Proceedings of the National Academy of Sciences, economic activity is still becoming more carbon-intensive. Since 2000, carbon output per dollar of productivity has been increasing by 0.3% per year, whereas during the previous 30 years, it was dropping by an average of 1.3% per year. The result, the team discovered, is that atmospheric carbon concentrations are now increasing by 1.93 parts per million each year--the fastest rate of buildup since monitoring activities began in 1959 and considerably higher than the 1.58-ppm average for the 1980s and the 1.49 ppm for the 1990s.
"Scenarios of energy use and CO2 emissions did not foresee the high levels of economic growth that we are currently observing," says geochemist and co-author Gregg Marland of Oak Ridge National Laboratory in Tennessee. Therefore, he says, it "will be important to keep watch over the next few years to see if the changing trend is a continuing one."
The paper presents "a consistent picture of the increasing accumulation of atmospheric CO2 and, hence, the increasing urgency to do something about it," says physical scientist S. Randy Kawa of NASA's Goddard Space Flight Center in Greenbelt, Maryland. But he cautions about jumping to long-term conclusions. "Just because the last 7 years have shown accelerating trends does not mean that the next 7 or 50 or 100 will be the same," Kawa says. "But they are what they are, and we need to pay attention."