Lessons from the ‘hiatus‘ controversy for the 2023/2024 warming spike

Global mean annual temperature in 2023 did end up much warmer than anticipated, stirring up a lively debate as to what the potential reasons might be. 2024 continued that trend with another record warm year on top, exceeding 1.5°C globally for the first time in all temperature data sets on an annual basis.

Here we argue (1) that 2023 is entirely compatible with our understanding of the climate system and (2) that the so-called ‘hiatus‘ controversy from the early 2010s should be used as a reminder to be rather cautious with claims that suggest something puzzling might be going on.

We present results from statistical and model based analysis, demonstrating that the magnitude of the new September and annual temperature record in 2023 lies within the range of possible record margins under current warming / forcing conditions. We also show that random shifts in large scale circulation patterns led to record warm conditions in the North Atlantic and Antarctica, contributing to the 2023 and 2024 outcome (in addition to anthropogenic factors as well as El Niño).

We also discuss whether or not these shifts are partially attributable (directly or indirectly) to the 2022 Hunga Tonga eruption or the regulation-induced sulphur emissions reduction in the global shipping sector.