Which gas is considered the principal greenhouse gas?

Carbon dioxide is considered the principal greenhouse gas due to its significant role in the Earth's atmosphere and its impact on climate change. It is released into the atmosphere primarily through human activities, such as the burning of fossil fuels and deforestation. Although other gases like methane and nitrous oxide are more effective at trapping heat on a per-molecule basis, carbon dioxide is far more abundant. Its long atmospheric lifetime means that it accumulates over time, contributing to the overall greenhouse effect.

The significance of carbon dioxide in climate change is underscored by its contribution to global warming, as it can stay in the atmosphere for centuries, thereby impacting the climate long after it has been emitted. When energy is absorbed and re-emitted by greenhouse gases, the resulting effect is to trap heat in the lower atmosphere, leading to increased global temperatures.

In summary, carbon dioxide stands out among greenhouse gases due to its prevalence, long-term persistence in the atmosphere, and critical role in the enhanced greenhouse effect, making it the primary gas of concern in discussions about climate change.