>It looks like even the recession can't slow down climate change.

New data from Norway's Zeppelin station show that, despite a global slowdown in industrial activity, the concentration of carbon dioxide in the atmosphere has hit a new high: 393.71 parts per million during the first two weeks of March, a 0.54 ppm increase from a year ago.

Carbon dioxide concentrations have been rising for years, but experts had predicted that the recession would curtail greenhouse gas emissions in 2009. Though this year's increase in concentration is less than the annual average of about 2 ppm between 1995 and 2005 and could partly be due to yearly variation, it's still an increase. 

Debate rages over how much carbon dioxide the atmosphere will be able to hold before the planet undergoes catastrophic climate changes. Scientists and policy-makers pegged this threshold at 550 ppm in the 1980s and '90s, but by the time the House got around to drafting its cap-and-trade bill they were using 450 ppm. Recently, NASA scientist James Hansen and activist Bill McKibben have led the drive to stabilize carbon dioxide concentrations at 350 ppm, which would involve reducing the current level by over 10 percent.     

Concentration measures also undergo variation unrelated to manmade emissions. In the Arctic region that houses the Zeppelin station, carbon dioxide concentrations usually peak in April, after rotting plants have released gases into the atmosphere all winter. As plants grow during the spring and summer and absorb carbon, concentrations tend to decline. But while these trends are cyclical, human-based emissions have steadily contributed to a carbon dioxide hike of well over 100 ppm since the Industrial Revolution. Read the Intergovernmental Panel on Climate Change's report for a prediction of what will happen if this long-term trend continues.