Earth’s atmosphere works something like a giant glass greenhouse. As the sun’s rays enter our atmosphere, most continue right down to the planet’s surface. As they hit the soil and surface waters, those rays release much of their energy as heat. Some of the heat then radiates back out into space.
However, certain gases in our atmosphere, such as carbon dioxide, methane and water vapor, work like a blanket to retain much of that heat. This helps to warm our atmosphere. The gases do this by absorbing the heat and radiating it back to Earth’s surface. These gases are nicknamed “greenhouse gases” because of their heat-trapping effect. Without the “greenhouse effect,” Earth would be too cold to support most forms of life.
But there can be too much of a good thing. Carbon dioxide is released when we use fossil fuels, such as coal, oil and natural gas. We burn these fuels, made from the ancient remains of plants and animals, to run electricity-generating plants that power factories, homes and schools. Products of these fossil fuels, such as gasoline and diesel fuel, power most of the engines that drive cars, airplanes and ships.
By examining air bubbles in ice cores taken from Antarctica, scientists can go back and calculate what the concentrations of carbon dioxide in the atmosphere have been throughout the last 650,000 years. The amount of carbon dioxide in the atmosphere has been climbing to where today it is 30 percent greater than 650,000 years ago. That rise in carbon dioxide “is essentially entirely due to the burning of fuels,” Susan Solomon says. She’s a senior scientist with the National Oceanic and Atmospheric Administration, in Boulder, Colo., and studies factors that affect climate.
Humans have further increased the levels of greenhouse gases in the air by changing the landscape. Plants take up carbon dioxide to make food in a process called photosynthesis. Once cut down, they can no longer take in carbon dioxide, and this gas begins building up in the air instead of fueling the growth of plants. So by cutting down trees and forests for farmland and other human uses, more carbon dioxide is also added into the atmosphere.
“We’ve always had some greenhouse gases in the atmosphere,” Solomon says. “But because we’ve burned a lot of fossil fuels and deforested parts of the planet, we’ve increased the amount of greenhouse gases, and as a result have changed the temperature of the planet.”