According to the United States Environmental Protection Agency , there is a decreasing trend in greenhouse gas emissions by gas from 2007 to 2012, mainly due to the increase in awareness. However, we are still generating about 6000 million tons of carbon dioxide per year.

Just to put the number in perspective, the CO2 emissions from a gallon of gasoline are only around 9000 grams. In addition, the average annual CO2 emissions of a typical passenger vehicle are about ( assume that an average person drives a 21.6 MPG car around 11,400 miles per year)

Annual CO2 emissions = (CO2 per gallon / MPG ) x miles = 9000 / 21.6 x 11,400 = 4.7 tons.

The total greenhouse gas emissions from transportation take up around 28% of the total GHS emissions. Fortunately, this means that there are still a lot of ways to reduce the total GHS emissions.