WMO: Update on anomalies 2023/4

The WMO launched its annual (now) STate of the Climate Report this week. As well as the (now) standard set of graphics related to Increased greenhouse gas concentrations, Increasing temperaturesReduction of glacier mass, etc., Zeke Hausfather and I wrote a brief synthesis about contributions to recent temperature anomalies.

Readers will remember our"https://www.realclimate.org/index.php/archives/2024/05/new-journal-nature-2023/" Title ="Nuevo Diario: Nature 2023previousThe discussions about anomalies in 2023 in particular, and the myriad of ideas that people have published to explain them. After our AGU session on the subject in December, we were asked to provide a brief synthesis of the results so far. As far as we know, this is the first quantitative attribution of anomalies to specific processes (but clearly it will not be the last word).

First, what are we trying to explain? They are not long -term trends! The temperature increase in ~ 1.5ºC from the baseline 1850-1900 is very clearly associated With increases in greenhouse gases, slightly (and decreasingly) modulated by changes in air pollution. Rather, we are trying to explain the waste of that trend: why any year (or year) is much warmer or fresher than the trend. There is always something, of course, the weather is variable, but by 2023 and 2024 the waste was higher than in any other year in decades. And, as you will remember, anomalies in 2023 were not well predicted in advance.

We evaluate the long -term trend using a smooth 20 -year -old in the WMO at 2022 (which was then projected to 2024), and define waste as the difference in that trend. A smooth Loess has a little more structure than a linear regression, and deliberately we do not use the last two data points to define it. There is a slight acceleration since 2000 in the softened curve, but this is not material for our analysis.

However, as you can see, the size of the residual by 2023 was comparable to 2016 and 1998 (years that began with great events of El Niño), and 2024 had the highest residual in decades despite the fact that the recent child was only a moderate event. We estimate the Enso impacts of a statistical regression of the waste against the FEB/MAR Nino34 index, which implicitly assumes that the child in 2023/24 had impacts similar to the previous events.

We estimate the other potential components of a combination of statistical modeling (for the solar cycle) and the published radiative forcing estimates (for the impact of marine shipping and Hunga Tonga emissions) converted into temperature anomalies using the fair emulator. Oriental Asian impacts₂ The emission changes (which have fallen precipitously since ~ 2005) are notable in global average trends, but because they have been relatively soft, the impact on waste 2023/4 is small.

Several things stand out. There is a clear contribution to waste in both years from shipping aerosol changes, as expected widely, but given the published estimates of radiative forcing, these contributions are only a fraction of the observed waste. In fact, we estimate that the contribution of the solar cycle has been comparably large. We estimate that the impact of Hunga Tonga (using the radiative forcing estimates of Sphoeberl et al (2024) It is really negative (from the SO₂ The contribution exceeded the aggregate stratospheric water vapor). We found that Enso had an insignificant impact in 2023, but it was a substantial taxpayer in 2024. And (something to my surprise) the impact of changes in the Aerosols in East Asia was also insignificant.

When summarizing contributions (assuming that they are independent and taking into account statistical uncertainties), the expected values ​​do not reach observations in 2023, but coincide quite well. Within the uncertainties (everything here is drawn with a 95%confidence interval), I could say that things align, but keep in mind that the greatest uncertainty comes from the modeling of the Enso effects. The most sophisticated modeling could be able to reduce uncertainty there.

Therefore, the conclusion is, to anyone’s great surprise, that 2023 is more difficult to explain than 2024. As the community moves to the appropriate synthesis using enm with updated forcing, there may be some adjustments in this image, the regionality of the effects of aerosol could magnify its impact on the global temperature temperature and the specified of the effect of the child that could inject an effect broader. Effect range for volcano and solar cycle components.

Other new studies

In some other articles on this topic they have also recently appeared:

• Allen and merchant (2025) Give a “new interpretation of the drivers of the Earth’s energy budget and their links with the warm -up of the ocean.”
• Terhaar et al. (2025) Look at the jumps in SST in climatic models and conclude that “a leap in the world temperatures of the sea surface that breaks the previous record in at least 0.25 ° C is an event of 1 in 512 years”
• Stefan and Grant Foster is also available a new predimpression: Rahmsorf and Foster (2025) Look at a corrected data set and conclude that SAT acceleration is evident.

Stay tuned!

References

1. Mr. Schoeberl, Y. Wang, G. Taha, DJ Zawada, R. Ueyama and A. Dessler, “Evolution of climate forcing during the two years after the eruption Hunga Tonga – Hunga Ha’apai”, Geophysics Research Magazine: atmospheresvol. 129, 2024. http://dx.doi.org/10.1029/2024JD041296

2. RP Allan and CJ Merchant, “reconciling the growing energy imbalance of the Earth with the warm -up of the ocean”, Environmental Research Lettersvol. 20, pp. 044002, 2025. http://dx.doi.org/10.1088/1748-9326/adb448

3. J. Terhaar, Fa Burger, L. Vogt, Tl Frölicher and Tf Stocker, “record the surface temperature jump of the sea in 2023–2024 unlikely but not unexpected”, “,” Nature2025. http://dx.doi.org/10.1038/s41586-025-08674-z

4. S. Rahmsorf and G. Foster, “Global warming has accelerated significantly”, 2025. http://dx.doi.org/10.21203/rs.3.rs-6079807/v1