Gavin Schmidt Admits He Hasn't Got A Clue Why 2023 Was So Warm But He Now Rules Out Hunga Tonga

NASA climate scientist Gavin Schmidt has just published an article in Nature:

For the past nine months, mean land and sea surface temperatures have overshot previous records each month by up to 0.2 °C — a huge margin at the planetary scale. A general warming trend is expected because of rising greenhouse-gas emissions, but this sudden heat spike greatly exceeds predictions made by statistical climate models that rely on past observations. Many reasons for this discrepancy have been proposed but, as yet, no combination of them has been able to reconcile our theories with what has happened.

El Niño — the inverse of La Niña — causes the eastern tropical Pacific Ocean to warm up. This weather pattern set in only in the second half of the year, and the current spell is milder than similar events in 1997–98 and 2015–16.

However, starting last March, sea surface temperatures in the North Atlantic Ocean began to shoot up. By June, the extent of sea ice around Antarctica was by far the lowest on record. Compared with the average ice cover between 1981 and 2010, a patch of sea ice roughly the size of Alaska was missing. The observed temperature anomaly has not only been much larger than expected, but also started showing up several months before the onset of El Niño.

So, what might have caused this heat spike? Atmospheric greenhouse-gas levels have continued to rise, but the extra load since 2022 can account for further warming of only about 0.02 °C. Other theories put forward by climate scientists include fallout from the January 2022 Hunga Tonga–Hunga Ha‘apai volcanic eruption in Tonga, which had both cooling effects from aerosols and warming ones from stratospheric water vapour, and the ramping up of solar activity in the run-up to a predicted solar maximum. But these factors explain, at most, a few hundredths of a degree in warming (Schoeberl, M. R. et al. Geophys. Res. Lett. 50, e2023GL104634; 2023). Even after taking all plausible explanations into account, the divergence between expected and observed annual mean temperatures in 2023 remains about 0.2 °C — roughly the gap between the previous and current annual record.

The ‘few hundredths of a degree’ claim is based on a paper which I wrote about here:

As I said at the time, the claim by Schoeberl et al 2023 is suspect because it models an equilibrium response after a quadrupling of atmospheric CO2. The HTHH eruption was clearly a very different non equilibrium event:

So the authors make a fairly good job of explaining why their surface temperature response to an increase in SWV is so very different from Wang et al (and Solomon et al): it comes down to the fact that they are simulating the equilibrium response after a quadrupling of CO2 concentration (resulting in a long term increase in SWV concentration) whereas Wang et al were considering the non-equilibrium response to different radiative forcings (e.g. short term natural fluctuations in SWV - including those due to volcanoes).

So in my opinion Gavin Schmidt unjustifiably rules out Hunga Tonga and then compounds his error by hinting darkly that we may now be in ‘unknown territory’ with current global warming (suggestive once again of the dreaded ‘tipping points’).

It could imply that a warming planet is already fundamentally altering how the climate system operates, much sooner than scientists had anticipated. It could also mean that statistical inferences based on past events are less reliable than we thought, adding more uncertainty to seasonal predictions of droughts and rainfall patterns.

Much of the world’s climate is driven by intricate, long-distance links — known as teleconnections — fuelled by sea and atmospheric currents. If their behaviour is in flux or markedly diverging from previous observations, we need to know about such changes in real time. We need answers for why 2023 turned out to be the warmest year in possibly the past 100,000 years. And we need them quickly.

This is nonsense. Scientists and their models got warming wrong and they got caught out by a natural event which they are loathe to give due credit to for much of the warming which occurred in 2023.