Radiative forcing
Radiative forcing is the change in Earth’s net downward radiative flux at the top of the atmosphere or tropopause caused by an external climate driver, expressed in watts per square metre. Positive forcing tends to warm the climate system; negative forcing tends to cool it. Effective radiative forcing includes rapid atmospheric and surface adjustments.
In simple terms
Earth receives solar energy and emits energy to space. A change in greenhouse gas concentrations, aerosols, solar output, volcanic particles, or surface reflectivity can disturb that balance. Radiative forcing quantifies the imposed energy-budget change, making different climate drivers comparable on a common physical scale. Definitions vary according to which rapid adjustments are included: instantaneous forcing excludes adjustments, while effective radiative forcing includes rapid responses but excludes the radiative response caused by global surface-temperature change. The forcing is a driver; the subsequent temperature-dependent processes are climate feedbacks.
Why it matters
Radiative forcing links a physical driver to its initial influence on Earth’s energy balance and underpins attribution, climate modelling, and emissions metrics such as global warming potential. Its sign and magnitude do not alone specify the final regional climate response, timing, or impacts, because feedbacks, ocean heat uptake, spatial patterns, and the persistence of the forcing agent also matter.
Example
Increasing atmospheric carbon dioxide reduces outgoing infrared energy, creating positive radiative forcing. The climate then warms, and temperature-dependent changes in water vapour, snow and ice, clouds, and outgoing radiation alter the response. Those later changes are feedbacks. Reflective volcanic aerosols can instead create negative forcing for a limited period by increasing reflected sunlight.
How it differs
Global warming potential
Radiative forcing is a physical change in Earth’s energy balance; global warming potential integrates the radiative forcing from a pulse emission over a chosen time horizon relative to carbon dioxide.