Multiple factors have contributed to the record rise. El Niño, the naturally occurring climate pattern that warms the eastern tropical Pacific, has been ongoing since last year. The change in ocean temperatures influences weather around the world, leading to drought in many parts of the tropics. The drought and heat that come with an El Niño event means that plants grow less, taking up less CO2 as a result. Increased wildfire activity also releases more CO2 into the atmosphere.

Burning fossil fuels is also a major driver. Emissions hit a peak last year, rising to 36.8 billion metric tons. That’s driven CO2 concentrations in the atmosphere higher, worsening a dizzying array of disasters, including heat waves, extreme rainfall, wildfires and floods, including amplifying some El Niño impacts.

“The emissions from the tropical forests are superimposed on these very large emissions from fossil fuel burning, which is bigger than ever,” says Keeling. “It’s not that El Niño events are unusual, it’s the fossil fuel burning is unusual in a historical sense. It’s an extreme. It’s never been higher.”