Greenhouse gases are natural and synthetic chemicals that absorb some of the Earth's outgoing radiation and trap heat in the atmosphere, causing climate changes on global and regional scales. These changes, known as the greenhouse effect, alter the Earth's energy balance and affect weather patterns. Carbon dioxide, methane and nitrous oxide are well-known greenhouse gases, but there are many other substances that have a significant impact on the climate system. Tracking trends of these other substances can be challenging, and data are often not available for many of them.
In general, the importance of a gas in the greenhouse gas mix depends on its absorption of the Earth's thermal IR radiation (often referred to as its radiative forcing) and its atmospheric lifetime and concentration. The former is determined by the intrinsic property of the gas itself and the latter by its competition for absorbing radiation in different parts of the spectrum (band overlaps).
Nitrous oxide is not considered a direct greenhouse gas because it does not absorb terrestrial IR radiation strongly enough, but it increases the concentration of other greenhouse gases such as methane and tropospheric ozone through its reaction with atmospheric HOHO, thus contributing to the formation of these gases.
Several human activities contribute to the production of greenhouse gases, especially CO2. These include fossil fuel combustion (e.g. for electricity generation, transportation and heating) and land clearing. To reduce these emissions, we can use alternative sources of energy such as solar panels and biodiesel and take a variety of other steps to lower our emissions. For example, replacing incandescent bulbs with fluorescents uses 75% less energy and reduces carbon emissions; driving a hybrid vehicle can lower emissions by up to 40%; and traveling on foot or riding a bike can decrease greenhouse gas emissions considerably.