Greenhouse gases (GHGs) are molecules that absorb and retain thermal radiation emitted by the Earth’s atmosphere, making the Earth warmer. These gases are important natural and human-caused atmospheric components. They also help regulate Earth’s temperature. Some of these gases remain in the atmosphere for a short time and have little impact on climate change; others, like carbon dioxide, stay in the atmosphere for a long time.
Human activities, especially fossil fuel combustion since the Industrial Revolution, are responsible for the steady increase in concentrations of greenhouse gases. These include CO2, water vapor, and methane. Some of these gases are natural, while others (like hydrofluorocarbons and chlorofluorocarbons) are synthetic and produced entirely by humans.
The relative impact of different gases is determined by their Global Warming Potential, or GWP. This is a measure of how much energy 1 ton of gas will absorb over a century, compared with the amount of energy absorbed by a ton of CO2. Gases with higher GWPs warm the atmosphere more than those with lower GWPs.
The amount of GHGs in the atmosphere is measured in parts per million, parts per billion, or even parts per trillion. These concentrations are related to the quantity of greenhouse gases emitted, but can vary from year to year depending on changes in economic activity and weather conditions. For example, a large increase in CO2 emissions during the 1980s was followed by a stabilization until 2007 when the rate of growth resumed, largely due to the rise in fuel use to power homes and cars and to the ongoing recovery from the coronavirus pandemic.
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