The 2023 heat spike: apocalyptic or unusual?

The Global Heat Anomaly 2023

Many climate scientists are very worried about the global heat anomaly seen in 2023, and for varying reasons. No single year has confounded their predictive capabilities more than 2023. They didn’t see it coming, but perhaps they were looking in the wrong direction?

Writing in the journal Nature, Gavin Schmidt of NASA’s Goddard Institute for Space Science says that:

“[the] 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.”

For the past nine months, average land and sea surface temperatures have exceeded records each month, sometimes by up to 0.2°C. This global heat event exceeds greatly forecasts by climate models. At the start of 2023, modellers put the chance of it being a record warm year at 20%, although this was actually just an educated guess. So from one point of view, 2023 has been a disaster for climate modelling. Many explanations have been proposed, but so far none of them – singly or in combination – can explain what happened. It wasn’t due to the El Niño, an upturn in oceanic temperature cycles, increased solar activity, or the reduction in aerosol shielding due to cleaner shipping fuels.

Javier Vinós, writing in Judith Curry’s blog, says that the January 2022 Hunga Tonga underwater volcanic eruption boosted stratospheric water vapour by a remarkable 10%, and is the most likely cause of the recent warming. The Hunga Tonga eruption produced an enormous amount of water vapour without any volcanic ash, which would normally bring a temporary cooling effect to the atmosphere, as in 1815 with the Mount Tambora explosion. ‘Unlike the lower troposphere, where the greenhouse effect is relatively saturated, the stratosphere, well above the Earth’s average emission altitude, experiences a much more pronounced effect from the addition of water vapour’, Vinós says.

The problem is that despite its less than once-in-a-century levels of violence, initial studies on the global impact of the stratospheric water vapour injections suggested that its effects would be minor. Clearly more work needs to be done; after all, could it merely be a coincidence that the global heat anomaly is adjacent to the Hunga Tonga event?

Unsurprisingly the 2023 temperature peak has sparked alarmist and apocalyptic predictions. Schmidt says if the anomaly does not stabilise by August the world will be in uncharted territory, and that the temperature of 2023 could imply that a warming planet is already fundamentally altering how the climate system operates, much sooner than scientists had anticipated.

But perhaps nothing fundamental has been altered and we have just witnessed the aftermath of a very rare event that shows us the power of natural climatic variations and that the science isn’t settled, or apocalyptic.

Vinós argues that we could see a reversing of all the warming caused by the Hunga Tonga volcano. When added to the decline in solar activity after the maximum of Solar Cycle 25, and a future ocean-current shift of the Atlantic Multidecadal Oscillation, we could see another global temperature hiatus similar to the one that ended with the 2015 super El Nino. ‘These are indeed interesting times in terms of climate dynamics’, observes Vinós.