Around the turn of the 20th century, Svante Arrhenius was the first to suggest that people could, through the burning of coal, increase the amount of greenhouse gases in the atmosphere and amplify the natural warming effect, thereby causing the atmosphere to warm more than it would through strictly natural processes.
When humans burn gasoline, coal, natural gas, and other common fuels to make electricity or drive cars, they release a substantial amount of carbon dioxide into the atmosphere. For every gallon (or liter) of gasoline your car burns, 1300 times that volume of CO2 is released (a gallon of gas weighs about 6 pounds or 2.8 kilograms, but the released CO2 would weigh over 19 pounds or 8.75 kilograms).
Greenhouse gases are emitted from power plants and cars, but also from landfills, from farms and cleared forests, and through other subtle processes.
Further more,To see how climate change affects different parts of the Earth, climate scientists break the models down into smaller pieces, calculate how small parts of the Earth’s surface react to the Sun and greenhouse gases, and then connect those small parts together, based on measurements of how the atmosphere and ocean interact.
To ensure the accuracy of the models at projecting future climate trends, the models are often run backwards in time to “retrodict” past climate changes, and then compared with paleoclimate observations. The models through this process have become remarkably accurate and give the climate research community confidence that the future projections are robust.’
An interactive map from the Environmental Protection Agency shows US sources of key greenhouse gases. The World Resources Institute cataloged (PDF) global sources of greenhouse gases in 2005.
In the 1950s, scientists began methodically measuring global increases in carbon dioxide. Since then they’ve been able to confirm that the increase has been caused primarily from the burning of fossil fuels (and through other human activities, such as clearing land, as well). This increase, and changes in the type of CO2 being added to the atmosphere provide the “smoking gun” that shows that humans are responsible for the increased levels of carbon dioxide in the atmosphere.