Which major greenhouse gas is most abundant in the atmosphere?

Water vapor is considered the most abundant greenhouse gas in the atmosphere. It plays a critical role in the Earth's climate system by helping to trap heat. Water vapor is unique among greenhouse gases because its concentration in the atmosphere is primarily controlled by natural processes, such as evaporation and condensation, rather than directly by human activities.

The presence of water vapor forms clouds and influences weather patterns, and it has a variable concentration depending on temperature and location. As the temperature increases due to other greenhouse gases like carbon dioxide, more water vapor enters the atmosphere, creating a feedback loop that can enhance the greenhouse effect.

While other gases, like carbon dioxide, methane, and nitrous oxide, are also significant contributors to human-induced climate change, their atmospheric concentrations are lower compared to water vapor. Carbon dioxide, although more impactful in terms of long-term climate change effects, does not occur in concentrations as high as water vapor. This reinforces why water vapor is identified as the most abundant greenhouse gas overall.