Erratum: Previous Gavin Schmidt Post

Eagle eyed readers may have spotted that I made an error in my post here:

I said:

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:

I was in fact confusing Schoeberl et al 2023 with this study by Wang & Huang in 2020, where they modelled the equilibrium response to stratospheric water vapour due to a long term quadrupling of CO2. My excuse is that both papers include Wang as an author and I’m sticking to it!

Schoeberl et al base their claim of ‘a few hundredths of a degree’ on something totally different. They basically sum up the instantaneous (non equilibrium) radiative forcings of aerosols and stratospheric water vapour and find that the aerosol forcing (cooling) more than compensates for the stratospheric water vapour warming:

The Hunga-Tonga-Hunga Ha'apai (HT) eruption produced increased stratospheric water vapor and aerosols primarily in the Southern Hemisphere. Jenkins et al. (2023) suggested that the increased stratospheric water vapor would warm the climate slightly, but their study neglected the role of volcanic aerosols in reducing the solar flux. We use a radiative transfer model to estimate the changes in downward IR flux due to the MLS observed enhanced water vapor layer, and OMPS-LP data to compute the stratospheric AOD. We parameterize the reduction in solar flux due to HT aerosols using past volcanic events (Table 1). Our results are nearly identical to Yu and Huang (2023) results for clear skies, non-volcanic conditions. We subsequently use their clear and all sky parameterizations to assess the direct solar forcing. The solar flux reduction by aerosols is larger than the net IR flux increase due to stratospheric water vapor. In other words, the direct solar radiative cooling associated with the HT aerosols overwhelms the enhanced thermal radiation from stratospheric water vapor plume. Our results are in good agreement with net radiative forcing changes estimated by Sellitto et al. (2022) and Zhu et al. (2022). We find that the zonal mean peak change in net radiative forcing occurs in May 2022, but the SH average forcing peaks in June/July as the constituents spread throughout the SH. Using the observed impact on tropospheric temperatures from Pinatubo as a scale, Hunga-Tonga would produce an SH annual average surface temperature change of less than −0.038°C for clear skies and −0.021°C for all skies.

This is interesting because I suggested at the beginning of August 2023 that the reason we hadn’t seen rapid warming immediately following the explosion was that the significant amounts of aerosols were having a cooling effect. These aerosols would have been flushed out of the atmosphere fairly rapidly (by summer 2023), but the water vapour would have remained (as confirmed by another scientific study); thus the sudden uptick in warming. It’s just a theory of course, but one which is lent credibility by observations and by the work of Schoeberl et al.

So here’s my suggestion: we are beginning to see rapid warming now, in summer 2023, because the radiative warming effect of the water vapour is no longer being cancelled by the aerosol cooling effect of Tonga. It’s as simple as that. On that basis, we can expect further warming over the next year or two and, with the possibility of a moderate El Nino developing in the central Pacific, that will add to the warming by the end of this year and we may be seeing a very significant rise in global temperature which of course the climate propagandists will attribute to anthropogenic greenhouse gases, so be warned; there could be much hysteria ahead, even the global declaration of a ‘climate emergency’.

If this is the case, then the 2023 warming spike will begin to reverse as soon as the more persistent stratospheric water vapour due to Hunga Tonga is itself removed from the atmosphere. At present, I am unaware of exactly how rapidly or slowly this will happen, and when it will happen - watch this space.