Increases in the Greenhouse Gases

Carbon dioxide, methane, nitrous oxide, and fluorinated gases all trap outgoing infrared radiation, but they don't do it equally. CO2 comes mostly from burning fossil fuels and deforestation, and once released it lingers in the atmosphere for centuries, slowly getting absorbed by oceans and plants. Methane comes from livestock digestion, rice paddies, landfills, and leaking natural gas wells; it traps heat far more efficiently molecule for molecule, but breaks down in the atmosphere in about a decade. Nitrous oxide, largely from fertilized soils, sits in between on lifetime but is roughly 300 times more potent than CO2 by mass. Fluorinated gases, used in refrigeration, are rare but trap enormous amounts of heat per molecule and can last thousands of years.

Because these gases differ so much in potency and lifetime, scientists use global warming potential, or GWP, to put them on one scale. GWP tells you how much more heat a given mass of a gas traps compared to the same mass of CO2 over a set time period, usually 100 years. Multiplying a gas's mass by its GWP converts it into CO2 equivalent, a single number policymakers can add across every gas a country emits.

This matters for feedback loops too. Arctic permafrost holds huge stores of frozen organic matter; as it thaws, microbes decompose it and release methane, which warms the atmosphere further and thaws more permafrost. That self-reinforcing cycle is why methane draws special attention even though CO2 is far more abundant, and it connects directly to the warming oceans and shifting habitats covered elsewhere in this unit.