Last year Earth warmed around 0.2 °C more than climate models predicted. While that may not seem like much in isolation, when you consider it’s a measure across an entire planet it amounts to a heck of a lot of unexplained heat.

“It’s humbling, and a bit worrying, to admit that no year has confounded climate scientists’ predictive capabilities more than 2023 has,” writes NASA climatologist Gavin Schmidt in an article for Nature.

“The 2023 temperature anomaly has come out of the blue, revealing an unprecedented knowledge gap perhaps for the first time since about 40 years ago, when satellite data began offering modellers an unparalleled, real-time view of Earth’s climate system.”

Schmidt warns if this unexplained anomaly doesn’t settle by August, in line with previous El Niño fluctuations, then we will be in uncharted territory.

Several theories have been posed for the excess heat beyond what is expected from the El Niño and known rates of increasing CO2. These include a decrease in surface-cooling aerosols from shipping after regulation changes in 2020; an increase in heat-trapping water vapor from the 2022 eruption of Hunga Tonga-Hunga Ha’apai; and peak activity in the current solar cycle sending more heat our way.

But even combined these all don’t fully account for observed extra heat, Schmidt argues.

The concern is we’re missing something critical in our understanding of Earth’s climate systems, that would explain an accelerated rate of warming, such as a potential miscalibration in the start date of humanity’s impact on the climate.

Being ahead of schedule would explain why extreme climate consequences, including deadly floods, fires, and storms, have been whacking us so hard and fast already.

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