Carbon dioxide emissions in the United States increased by approximately 2.9% between 1990 and 2017. Because fossil fuel combustion is the most important source of greenhouse gas emissions in the United States, changes in emissions The combustion of fossil fuels has historically been the factor with the greatest effect on trends in total emissions in the US Changes in CO 2 emissions from the combustion of fossil fuels are influenced by many factors a short and long term, such as population growth, economic expansion, changes in energy prices, new technologies, behavioral changes, and seasonal temperatures. Between 1990 and 2017, the increase in CO emissions2 corresponded to higher energy consumption due to expanding economies and populations, including overall growth in emissions from higher travel demand.