But high-altitude carbon emissions are reckoned to be more damaging than low-level ones, although nobody is sure by exactly how much.

ECONOMIST: Flying and climate change

Particularly damaging was an EPA rule finalized in February 2012 that created new emissions standards for coal- and oil-fired electric utilities.

FORBES: The EPA's Lisa Jackson: The Worst Head of the Worst Regulatory Agency, Ever

"There is a huge challenge ahead to reduce carbon dioxide emissions to stay below 2C of global warming, and without damaging the economy, " he said.

BBC: 2011 is UK's second warmest year on record - Met Office

One of the most damaging proposals is a cap-and-trade system to limit greenhouse gas emissions.

FORBES: Brrr!