Fossil-fuel emissions rose again last year, yet NOAA's Mauna Loa record shows the annual increase in atmospheric carbon dioxide dropped from 3.33 to 2.23 parts per million, and 2026 is running slower still. The Global Carbon Budget puts the swing down mainly to natural sinks.
At NOAA's Mauna Loa observatory, carbon dioxide (CO2) rose by 3.32 parts per million (ppm) in 2023 and 3.33 ppm in 2024, then by 2.23 ppm in 2025. That is a 33% fall in a single year, and the lowest annual rise since 2022. The ten-year average for 2015 to 2024 is 2.64 ppm.2
Human emissions did not fall. The Global Carbon Budget estimates that fossil CO2 emissions rose by about 1.0% in 2025, with a range of 0.2% to 1.7%, to an expected 38.1 billion tonnes of CO2. Its own measure of the global atmospheric increase tells the same story as NOAA's: a record 3.7 ppm in 2024, then a preliminary 2.1 ppm in 2025.3 The two sets of numbers differ slightly because the Global Carbon Budget uses a global average and NOAA's series is a single site.
Around half of what humans emit stays in the air; the rest is taken up by oceans and land. The Global Carbon Budget attributes 2024's record rise mainly to the 2023/24 El Niño, when the land sink fell to 1.9 billion tonnes of carbon from a decade average of 2.4, and links the 2025 slowdown to the end of that El Niño.3 This is the authors' attribution of a one-year swing; it does not show that emissions have stopped mattering.
The monthly record suggests the slowdown has continued. Comparing each month with the same month a year earlier, the rise averaged 3.53 ppm over January to September 2024, 2.86 ppm in 2025 and 1.82 ppm in 2026. Individual months are noisy, ranging from 1.26 ppm in July to 2.26 ppm in February this year, and September's value is provisional.1
The pause may not last. Copernicus reported in September that El Niño conditions were present in the tropical Pacific and forecast to strengthen, potentially into one of the strongest on record.4 Given what happened in 2024, one reading is that a stronger El Niño would reduce natural uptake again. That is an inference from the Global Carbon Budget's account of the last event, not a forecast of 2027's rise.
One station is not the planet, and one year is not a trend: the annual rise swung between 1.8 and 3.3 ppm in the last four years alone. The Global Carbon Budget's 2025 emissions and growth figures are preliminary, and its fossil-emissions range (0.2% to 1.7%) is wide.3 Mauna Loa's recent values are subject to recalibration, and NOAA has said final-year data can change.2