The NOAA Annual Greenhouse Gas Index (AGGI)
NOAA Global Monitoring LaboratoryLive page, updated annually. Current edition reports the 2024 data year and was last updated in autumn 2025 — date-stamp any republication.public-domainRead the original
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NOAA's Annual Greenhouse Gas Index measures the change in radiative forcing from long-lived greenhouse gases relative to 1990. For 2024 the index stood at 1.54, meaning effective radiative forcing from these gases was 54 percent greater than in 1990. Carbon dioxide in the marine boundary layer reached 422.80 parts per million in 2024, and the increase over the following twelve months was a record 3.72 parts per million. Methane reached 1929.56 parts per billion and rose 7.1 parts per billion during the year; nitrous oxide reached 337.71 parts per billion, rising 1.02. Carbon dioxide contributed 2.33 watts per square metre of effective radiative forcing, 66 percent of the total, with methane second at 0.57 watts per square metre, or 16 percent. Halocarbons including CFCs, HCFCs and HFCs contribute roughly 12 percent and nitrous oxide about 6 percent. Total forcing from these gases since pre-industrial times is 3.54 watts per square metre.
Extract
"The AGGI quantifies radiative forcing from long-lived trace gases and its change over time…formulated to provide an understanding of the change in radiative forcing in any given year relative to 1990, which was an important reference year in early global climate agreements." "For 2024, the AGGI was 1.54, which represents a 54% increase in effective radiative forcing from these gases since 1990." "The atmospheric abundance of methane (CH4) reached 1929.56 ± 0.61 ppb in 2024… The annual methane increase during 2024 was 7.1 ± 0.6 ppb." "Carbon dioxide was by far the largest contributor to effective radiative forcing from these gases (2.33 W m-2, or 66% of the total) and methane was the second largest contributor (0.57 W m-2, or 16% of the total)." "the extra 3.54 W m-2 of heat retained in 2024 by the increases measured in long-lived greenhouse gas abundances since pre-industrial time represents an increase of 1.47% in the amount of heat retained in the Earth system."
NOAA Global Monitoring Laboratory · public-domain · Read the original
The MyGreenSuit briefing
Commentary by MyGreenSuit, not the words of NOAA Global Monitoring Laboratory.
This is the beat's founding document, and it fits on one page.
Carbon dioxide accounts for 66 percent of the radiative forcing from long-lived greenhouse gases. Methane is 16 percent, halocarbons around 12, nitrous oxide about 6. So roughly a third of the problem is not CO2 — and it receives nothing like a third of the policy attention, the reporting or the corporate disclosure.
The reason to trust these numbers over almost anything else in the field: they are direct atmospheric measurements, not inventories. Nobody self-reports to NOAA. When an inventory and this dataset disagree, this one is the referee.
The 2024 carbon dioxide jump of 3.72 parts per million is the largest in the record, and it happened in a year of continued renewable expansion. Concentration responds to cumulative emissions, not to the rate of change in the electricity mix — a distinction that gets lost constantly.
One housekeeping point: the index is a live page that updates annually. Date-stamp whichever version you cite.