Every year, forests and soils absorb some of the carbon dioxide emitted by factories and cars. It is like the planet taking a breath. But in 2023, that breath was weak. Atmospheric carbon dioxide grew at a rate of 3.66 parts per million per year, faster than in any year in the past 45 years of measurements.

The culprit was the warm El Niño current in the Pacific Ocean. It alters weather worldwide and brings drought to tropical forests. When trees lack water, they close the pores on their leaves to avoid drying out. With water, carbon dioxide uptake also stops. The forest stops growing and absorbing carbon, while the soil continues to breathe it back out.

Previously, such disruptions were only noticed a year later, when full reports came out. Now scientists have combined computer models of forests, rapid calculations for the ocean, and satellite measurements of carbon dioxide. It is like a pulse oximeter on a finger: the planet's breathing is visible almost immediately. The ocean tried to help and absorbed a bit more, but that only covered a small fraction of what the land failed to take up.