Gavin Schmidt Comes Clean About The Unexpectedly Very Warm Year Of 2023

Here it is at last: the first real admission from a climate scientist that they got it badly wrong about 2023, how the year greatly exceeded predictions in terms of warmth and why that might be the case. Here’s Gavin on Twitter:

This is what the post at RealClimate says [my bold]:

For the last few years (since at least 2016), I’ve shared predictions for the next annual global mean surface air temperature (GMSAT) anomaly based on the long term trend and the state of ENSO at the start of the year. Generally speaking, this has been quite skillful compared to persistence or just the long term trend alone – the eventual anomaly was consistently within the predicted bounds. Until 2023.

Here was Gavin’s projection (in light blue) vs. the actual data for 2023 (in brown). You can see that the large upper error bars don’t even come near the actual 2023 figure. The projection was way off.

Gavin describes the method he uses, which involves (naturally enough) examining the long term trend and taking into account likely ENSO conditions:

As described in my original post on 538, I take a loess smooth for the GISTEMP long term trend (using roughly 20 year smoothing) and add a term based on the linear regression of the beginning of the year Multivariate ENSO Index (MEI2) (similar to Nino34) to the detrended anomalies (not including some big volcanic years). This makes sense since, historically, the interannual variations in GMSAT were largest in the first half of the year and dominated by the phase of ENSO (El Niño or La Niña). This pattern was important for recent record or near-record years like 2016 or 2020 which started with El Niño, as well as below-trend years like 2017, 2021 etc. that started with La Niña. The development of the ENSO phase in the latter part of the year (which peaks around December/January) generally has less of an impact because of the lag of ~3 months or so of its affect on global temperatures.

Gavin makes it clear, as I have done until I am blue in the face in numerous posts on Substack, that the El Nino conditions developing later in the year do not have much of an effect upon the overall global temperature for that year; the real effect comes in the following year. So Gavin’s projection was based on an assessment of existing ENSO conditions, figuring that even if an El Nino developed during the year, it would not significantly affect global temperature.

Gavin then speculates on the reasons why he might have got 2023 so wrong:

This could be due to a real anomaly in the interannual variability that was outside the 95% expectation, a mis-specification in the statistical model (e.g. we could have included an autumnal ENSO state as an additional predictor, or taken predicted forcings (solar, aerosols, volcanoes) into account), or something extra that we just haven’t seen before.

But how are we going to find out? What happens in 2024 will be important. Does it go back to being predictable based on ENSO (in which case 2024 is expected to just be a little warmer than 2023), or does the positive anomaly persist? We will also be seeing more comprehensive estimates of the impact of the Hunga-Tonga eruption, and also of the impacts of the decreases in marine shipping emissions. It might be that the initial estimates of their impacts were underestimated. We will also see more in depth explorations of the spring to fall anomalies in the North Atlantic/North Pacific which contributed strongly to the temperature changes, but aren’t obviously related to El Niño.

If nothing else, 2023 reminds us that the climate system still has surprises for us, and that this would be a very bad time to our eyes off the ball.

Well buy that man a beer! I haven’t read such an open and honest admission from a climate scientist who got it wrong . . . . . ever! Note, he doesn’t even mention that ‘climate change’ might be responsible for the sudden acceleration in global temperature, presumably because he’s a physical scientist and he realises how absurd a proposition that is. One thing he does mention is the rather odd north Atlantic and north Pacific sea temperature anomalies, which is something I would like to look at in a forthcoming post, because they undoubtedly contributed in some way to the warmth in 2023. I’m still not convinced by the shipping aerosol emissions explanation, so that leaves the possibility that the ‘small effect’ of Hunga Tonga might not have been so small after all. Well what do you know?

Update: 06/01/24

Zeke Hausfather has also tweeted about 2023:

Just two years have been well outside expectations: 1992 a lot colder due to Pinatubo eruption and 2023 a lot warmer due to . . . . . . . ? I wonder what?