Radiative Forcing Calculator

Radiative forcing (ΔF) measures the change in energy flux in the atmosphere caused by a change in greenhouse gas concentration, expressed in watts per square meter (W m⁻²). A positive value means more energy is being trapped, leading to warming. It is the standard metric used by the IPCC and NOAA to quantify each gas's contribution to climate change.

This calculator uses the NOAA AGGI simplified radiative forcing expressions: ΔF(CO₂) = 5.35 × ln(C/C₀), ΔF(CH₄) = 0.036 × (√M − √M₀), and ΔF(N₂O) = 0.12 × (√N − √N₀), where C, M, and N are current concentrations and C₀, M₀, N₀ are baseline concentrations. These are the same formulas published by NOAA's Global Monitoring Laboratory.

The standard pre-industrial (year 1750) baseline concentrations are approximately 278 ppm for CO₂, 722 ppb for CH₄, and 270 ppb for N₂O. These are the reference values used by NOAA and the IPCC to define the starting point before significant human influence on the atmosphere.

The AGGI, published annually by NOAA's Global Monitoring Laboratory, quantifies total radiative forcing from long-lived greenhouse gases relative to the 1990 baseline. It combines CO₂, CH₄, N₂O, CFCs, HCFCs, and HFCs. As of 2024, the AGGI indicates radiative forcing is 54% greater than in 1990, with CO₂ being the dominant contributor.

CO₂'s absorption bands in the infrared spectrum become saturated as concentration increases, meaning each additional molecule has a smaller warming effect than the last. A logarithmic relationship captures this diminishing return accurately. CH₄ and N₂O, being less concentrated, follow a square-root relationship instead.

Per unit of concentration change, methane is far more potent than CO₂ — methane has a Global Warming Potential (GWP) of about 84 over 20 years and 28 over 100 years. However, because atmospheric CH₄ concentrations are much lower than CO₂ (ppb vs ppm), CO₂ still dominates the total accumulated radiative forcing observed today.

CO₂-equivalent (CO₂-eq) converts the combined radiative forcing of all greenhouse gases into the single CO₂ concentration that would produce the same warming effect. It allows scientists and policymakers to express the collective impact of multiple gases in a single, intuitive number. This calculator derives CO₂-eq from total ΔF using the inverse of the CO₂ forcing formula.

This tool focuses on the three primary long-lived greenhouse gases — CO₂, CH₄, and N₂O — for which simplified forcing expressions are well-established. Halogenated gases like CFCs, HCFCs, and HFCs also contribute to radiative forcing but require individual forcing coefficients for each compound. The NOAA AGGI report tracks these additional gases in its full dataset.