The greenhouse effect is the process where greenhouse gases in the atmosphere, like carbon dioxide (CO2) and methane (CH4), absorb heat from the sun in order to warm the Earth. The greenhouse effect is natural and helps make it possible for there to be life on Earth, but since the Industrial Revolution in the 1800's, humans have been putting much higher levels of greenhouse gases (GHGs) in the atmosphere. As a result, more heat is being trapped in Earth's atmosphere, and warming is happening at unnatural and alarming rates.

Fossil fuels are non-renewable, naturally-occurring energy sources such as coal, oil, and natural gas (not to be confused with gasoline, which is derived from oil). When fossil fuels are extracted, processed, and burned for energy, greenhouse gases such as carbon dioxide, methane, and nitrous oxide are released into the atmosphere.

From the EPA and NASA, the five main greenhouse gases are:

• carbon dioxide (CO2): a gas released when we breathe or when we burn fossil fuels, or during the production of cement, as well as when things decompose or volcanos erupt. Plants use carbon dioxide to photosynthesize. Carbon dioxide is an extremely potent GHG; according to NASA, carbon dioxide doesn't get destroyed over time, and so small increases in its levels have huge effects on the Earth's temperature.

• methane (CH4): a gas released when we burn fossil fuels or through agricultural processes, land use, and the decomposition of waste in our landfills. Raising cattle and producing rice also contribute greatly to methane levels. Methane is an extremely potent GHG.

• water vapor (H2O): a gas released through evaporation (when liquid water becomes water vapor, usually because of heat), sublimation (when solid water becomes water vapor, usually because of heat and pressure), and transpiration (when plants release water vapor). Water vapor might seem like an unlikely GHG, but it's potent in its own way: it amplifies the effects of the other GHGs around it. Water vapor is also the only GHG that both causes and is caused by climate change due to the water vapor positive feedback loop, a vicious cycle where levels of water vapor rise as the atmosphere gets hotter, and the atmosphere gets hotter as levels of water vapor rise.

• nitrous oxide (N2O): a gas released through agriculture in the form of nitrogen fertilizers or through the burning of fossil fuels. Nitrous oxide is also known as laughing gas and is used for anesthesia.

• fluorinated gases, AKA F-gases: synthetic gases used in household products such as refrigerators, air conditioning, heaters, insulation, power lines, etc., and in commercial and industrial products and activities. Hydrofluorocarbons, perfluorocarbons, sulfur hexafluoride, and nitrogen trifluoride are F-gases. F-gases are extremely potent---according to the European Commission, "their warming impact is often thousands of times higher than that of carbon dioxide."

A carbon sink is something that absorbs and stores carbon dioxide from the atmosphere, thus removing it. The ocean is an example of a carbon sink because phytoplankton in the waters absorb carbon dioxide to use for photosynthesis, and because carbon dioxide naturally dissolves in water.

Mangrove forests and peatlands are also examples of carbon sinks.