At least, according to the US Environmental Protection Agency. Of course, there is still some way to go before this "pollutant" is controlled under the Clean Air Act, and it is conceivable that Congress will pass legislation aimed at controlling emissions in the meantime (but I wouldn't put money on it).
Carbon dioxide is essential for life. Without it, plants could not photosynthesise and, without plants, there would be no animal life, or anyone to write or read this blog. Horticulturalists deliberately boost the level in the air in greenhouses to increase their crop yields. Humans and all other animals add more carbon dioxide to the atmosphere every time they exhale. But, because the IPCC has deemed it to be the major driver of recent changes to the climate (despite there being no direct evidence to support this view), the EPA has now ruled that it can harm humans and therefore can be controlled under the CAA.
If this is taken to its logical conclusion, and carbon dioxide is treated in the same way as truly harmful gases such as sulphur dioxide, the impact on the US economy is likely to be severe, and both the American public and the Obama administration will have cause to regret it.
Martin Livermore is the Director of The Scientific Alliance