the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 02 Jan 2026
Attribution of the 2025 Mediterranean Marine Heatwave to Climate Change Using Analogues
Abstract. The Mediterranean Sea experienced a record-breaking marine heatwave in 2025, raising questions about the influence of human-induced climate change. Using an analogue-based attribution approach, we compared historical sea surface temperature (SST) patterns from ERA5 reanalysis (1950–2024) to those observed during the event. By identifying the most similar SST anomaly patterns in a past period (1950–1986) and a more recent one (1987–2024), we assessed changes in SST and related atmospheric variables. We find that, under present-day climate conditions, analogous patterns result in significantly higher SST anomalies and stronger atmospheric responses – such as warmer near-surface air temperatures and intensified radiative fluxes – compared to the past. Statistical tests confirm that long-term warming trend has amplified Mediterranean SST extremes by up to 1.5 °C and associated heat exchange processes, though shifts in large-scale natural climate variability may also influence these outcomes, complicating attribution. Nonetheless, the dominant contribution to the 2025 marine heatwave severity is attributable to anthropogenic forcing. This study proves the effectiveness of the analogue method for assessing extreme events, also including marine heatwaves, in a warming Mediterranean context.
Status: open (until 13 Feb 2026)
- RC1: 'Comment on egusphere-2025-5055', Anonymous Referee #1, 18 Jan 2026 reply
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- 1
Summary: The manuscript presents a novel application of the analogue method to attribute a Mediterranean heat wave to anthropogenic climate change. Although the application of the analog method for attribution is not new, this study adopts a different perspective: instead of searching for analogs of the atmospheric circulation and then comparing the observed extreme with those analog dates, this study searches for analogs dates of the observed extremes and then compares the atmospheric circulation of those dates with that observed at the dates of the extreme.
The conclusion reached for this particular Mediterranean heat wave is that the atmospheric dynamics in the past, while similar to that observed in the extreme, were linked to higher radiative and thermodynamic forcings.
Recommendation: I found the study interesting and, as I wrote above, considering this novel perspective that complements the standard application of the analog method for attribution. I have a recommendation that the authors may want to consider in a revised version
Main points:
1) The title and the abstract do not suggest that the perspective adopted in this study is different from other applications of the analog method. So the authors could better highlight this novel aspect. When reading the title, I first thought that this would be 'just another attribution study'. However, it is not, but this becomes clear when reading the complete manuscript. So I would recommend amending the title and the abstract.
2) In the conclusions section, the authors fall into their own trap. and write some sentences as if the conclusions came from a standard analog-attribution study. For instance, in line 389 they write 'This approach yields a physically transparent storyline: given the same atmospheric/oceanic setup that lead to the 2025 heatwave, a mid-20th-century climate would have produced a far less severe event'.
However, this is not what the study has done. It has not explored the outcome of the *same* (or similar) atmospheric/oceanic set up - it has explored the differences in the predictors of analogous heat waves
3) This different attribution scope, though interesting, makes it more difficult to quantify the impact of climate change. In the traditional approach, the difference between, say, the mean of past analogs and the observed extreme would be the climate change signal. But how can one quantify, with the approach presented in this manuscript, the contribution of climate change? Actually, the authors do not provide a number, perhaps because it is indeed more difficult to obtain.
This should be discussed.
Minor points
4) 'we compared historical sea surface temperature (SST) patterns from ERA5 reanalysis (1950–2024) to those observed during the event.'
The SST from the ER5 reanalysis come from two different sources, as the manuscript clearly states, depending on the period. However, in neither of these two periods are the SSTs a 'reanalysis' product in the classical sense. The OSTIA SSTs are indeed the result of a data assimilation methodology, but the 'model' is very simple, just persistence of the previous time step. A reader may think that SSts are also the result of data assimilation of observations and a proper ocean model.
5) Figure 1. 'Time series of daily sea surface temperature (SST) anomalies averaged (standard deviation
shaded in grey)'
I cannot see the shaded area in the downloaded pdf file. Perhaps the rendering of the figure is not totally correct
6) Section 5 consists of just one big paragraph (!). I would recommend splitting the paragraph, perhaps by the variables being described, to help the reader.
7) 'STR (q–t) presents positive Present–Past differences, implying reduced net longwave loss in the present climate, consistent with a warmer, moister atmosphere returning more longwave radiation to the surface (Trenberth et al., 2015; Vautardet al., 2023)'
I think this paragraph and the corresponding figure warrant a more detailed discussion or description. In principle, attributing it to climate change would entail stronger long-wave forcing from greenhouse gases. Feedbacks increase specific humidity, thereby amplifying the greenhouse effect. But in theory, another scenario is possible: solar radiation increases, warming the ocean surface and increasing specific humidity. In this scenario, anthropogenic climate change would not be ultimately responsible, or only indirectly through reduced cloudiness. So there are subtle questions to discuss based on this figure.
A clean attribution would find that the same MHW is linked to a similar or smaller solar radiation and to increased longwave radiation. I am aware that this reduces the number of possible analogs, but , again, this seems to me to be a complication of this novel attribution approach.