This page shows the atmospheric concentrations of the three major greenhouse gases — carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) — over the past 800,000 years. The data comes from air bubbles trapped in Antarctic ice cores, extended to the present day with direct atmospheric measurements.
For 800,000 years, these gases oscillated within natural bounds as Earth cycled between ice ages and warm periods. CO₂ never exceeded 300 ppm. Since the Industrial Revolution, all three have risen sharply beyond any level seen in this record — and the rate of increase is at least 10 times faster than any natural change in the ice-core record.
The data was compiled by the U.S. Environmental Protection Agency (EPA) as part of their Climate Change Indicators in the United States report (last updated June 2024). After the EPA datasets were taken offline, Leon Simons preserved a public backup.
The sidebar calculates the radiative forcing — the change in Earth's energy balance caused by each gas — using the standard simplified formulas from Myhre et al. (1998) as adopted by the IPCC:
These three gases together account for approximately 3 W/m² of forcing. Including halocarbons, ozone, and other minor gases brings the total to approximately 4 W/m² (IPCC AR6, 2021). The CERES satellite measures Earth's actual energy imbalance at approximately 1 W/m² — the difference is offset by cooling aerosols (~1 W/m²) and warming that has already been expressed in rising surface temperatures (~2 W/m²).
References: Lüthi et al. 2008 (EPICA CO₂), Loulergue et al. 2008 (EPICA CH₄), Schilt et al. 2010 (EPICA N₂O), Keeling et al. 1976 (Mauna Loa), Myhre et al. 1998 (forcing formulas), IPCC AR6 WG1 Chapter 7 (2021).