While global carbon emissions grow every year, year-to-year carbon emissions in the USA have been as likely to go down as up over the last ten years. From 2003 to 2012, US carbon emissions have been both down and up in 5 years. The down years were 2006, 2008, 2009, 2011, and 2012.
Interestingly, emissions declines are no longer simply a product of a contracting economy, although the deep recession from November 2007 through 2009 was a major cause of carbon decreases in 2008 and 2009. Importantly, carbon emissions actually declined in three years when the GDP grew--2006, 2011, and 2012. Declining carbon emissions, even when the economy grows, demonstrates that the economy is becoming less carbon intensive as a result of rising energy efficiency and market share gains of lower or zero carbon fuels like biofuels, natural gas, wind and solar.
Yet, just a change in the market share of coal and gas in electricity production can make the difference between total carbon emissions rising or falling from year to year. Indeed, rising coal generation in 2013 makes it highly probable that US carbon emissions will increase in 2013 over 2012.
The fact that US carbon emissions fell in absolute numbers in 5 of the last 10 years is a very different pattern, compared to the 12-year period from 1990 to 2002, when carbon emissions fell just twice. In that period, emissions fell only in 1991 and 2001, years when the economy was in recession.
With the rise of energy efficiency, zero carbon wind and solar, and the displacement of coal and oil by lower carbon biofuels and natural gas, US carbon emissions now have and can fall in years when the economy grows. That's a good fact that must be repeated.