Daniel Grossman Posted almost 3 years ago Happening Now: Live Q&A with TED Books Author Daniel Grossman on "Deep Water" and the Science of Rising Sea Levels With respect to CO2 output from the US, I'd make to some cautious comments. First, since it just happened and was not part of a policy to make it happen, we can't reply on the drop continuing. I bet part of the drop has to do with the current recession we're in. We hope that our economy will recover somehow and we wouldn't want that to come with renewed growth and CO2 emissions. Some of the reduction probably came from increased use of natural gas. The new technique of hydrofracturing to extract national gas (fracking) has brought down the price of natural gas, which produces less carbon dioxide per unit of energy. That's good in principle. But in practice fracking also releases a fair amount of natural gas into the atmosphere. Natural gas also causes the greenhouse effect, much more powerfully than carbon dioxide. So if even a small fraction of the natural gas escapes into the air before it's collected, the benefits of using natural gas are wiped out.