The nations of the world agreed in 1992 at the Earth Summit in Rio de Janeiro to the U.N. Framework Convention on Climate Change. The goal of the UNFCCC is to stabilize greenhouse gas concentrations "at a level that would prevent dangerous anthropogenic (human induced) interference with the climate system." It states that "such a level should be achieved within a time-frame sufficient to allow ecosystems to adapt naturally to climate change, to ensure that food production is not threatened, and to enable economic development to proceed in a sustainable manner."
U.S. energy-related carbon dioxide (CO2) emissions totaled 2,530 million metric tons in the first six months of 2016. This was the lowest emissions level for the first six months of the year since 1991, as mild weather and changes in the fuels used to generate electricity contributed to the decline in energy-related emissions. EIA's Short-Term Energy Outlook projects that energy-associated CO2 emissions will fall to 5,179 million metric tons in 2016, the lowest annual level since 1992.
Changing fossil fuel consumption mix. Coal and natural gas consumption each decreased compared to the first six months of 2015. However, the decrease was greater for coal, which generates more carbon emissions when burned than natural gas. Coal consumption fell 18%, while natural gas consumption fell 1%. These declines more than offset a 1% increase in total petroleum consumption, which rose during that period as a result of low gasoline prices.
In a 2015 report, the EIA noted, "Natural gas emissions have risen every year since 2009. Because it is the least carbon-intensive fuel, subsitution of natural gas for other fossil fuel inputs has served to mitigate overall CO2 growth in the industrial sector."
Those who worry about man-made global warming should thank shale gas fracking for this result.