The greenhouse effect refers to the ability of certain gases in the atmosphere, such as water vapor, carbon dioxide, nitrous oxide, and methane, to trap heat reflected by Earth's surface. Since the start of the Industrial Revolution, greenhouse gases such as carbon dioxide and methane have greatly increased.

Respiration by living things, together with other natural activities, produces carbon dioxide. In respiration, plants and animals break down glucose and release carbon dioxide and water. Respiration occurs at night as well as during the day. The forests and oceans, acting as sinks, absorb carbon dioxide, maintaining a fairly consistent level of carbon dioxide in the atmosphere. In the process of photosynthesis, plants use carbon dioxide and water to produce food and oxygen in the presence of sunlight. In oceans, CO₂ is absorbed by phytoplankton that use the carbon in CO₂ to create their skeletons, which are made of calcite (CaCO₃).

While these natural processes help maintain a healthy balance for ecosystems, human activities have now tipped the delicate balance. This increase in CO₂ has caused the amount of energy trapped within the atmosphere to increase, thus causing average temperature to rise. Today, most scientists agree that human activities, like driving less efficient cars and trucks and burning fossil fuels for home heating, have altered Earth's atmospheric chemistry. In fact, our heavy use of fossil fuels is the primary cause of increased carbon dioxide concentrations.

Research scientists like those at Biosphere 2 Center in Arizona are studying how various ecosystems, such as tropical rainforests, coral reefs, and cottonwood forests respond to increased levels of CO₂. They are also looking into whether we should capture and store CO₂ at the bottom of the ocean floor, where the combination of high pressure and low temperatures would make the carbon dioxide more dense than the surrounding water. This process is still being researched because it would pose risks to ocean life, and there is the possibility that unless the CO₂ is confined to deep areas it could be carried into shallow areas where it may reenter the atmosphere.