What are greenhouse gases and why do they matter?
Greenhouse gases (GHGs) are a category of gases that absorb heat energy emitted from the planet's surface and they remain in Earth's atmosphere for a long time (from decades to centuries). Though they make up only a small portion of the atmosphere (less than 1% of all air molecules), GHGs absorb a significant amount of heat energy and re-radiate some of it back toward the surface. They're called "greenhouse gases" because they trap heat near the Earth's surface in a manner somewhat similar to how a greenhouse allows in the sun’s rays and then holds in the resulting heat.
By adding more GHGs, like carbon dioxide and methane, to the atmosphere, humans are causing average global temperature to rise at an unprecedented rate. Earth has warmed by an average of 0.11°F (0.06°C) per decade since 1850, or about 2°F (1.1°C) in total. If yearly emissions continue to increase as rapidly as they have since 2000, climate models project that by the end of this century global temperature will be between 2.7°F (1.5°C) warmer than the 1901-1960 average, and possibly as much as 7.9°F (4.4°C) warmer, which would be catastrophic to human civilization.
Scientists warn that if our world warms by 2.7°F (1.5°C) or more above pre-industrial temperatures, then there will very likely be harmful impacts to human health and well-being as well as human-built environments and natural systems.
Download the Climate Change 2023 Synthesis Report PDF