This month’s open thread for climate topics. Please try to stay focused on climate instead of generic (and tedious) political sniping.
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172 Responses to "Unforced Variations: Apr 2025"
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FYI:
“Donald Trump’s administration has dismissed all contributors to the US government’s flagship study on how to prepare for climate change impacts, prompting strong criticism from experts over a ‘senseless’ move. The climate assessment is used by federal and local governments to understand how to prepare for climate crisis impacts including from extreme heat, hurricanes, flooding and drought.
“The dismissal of nearly 400 contributors, who are scientists and other experts, to the sixth National Climate Assessment (NCA), which is mandated by Congress, leaves the future of the report in doubt since the multi-year, peer-reviewed analysis is due for publication in 2028.”
https://www.theguardian.com/us-news/2025/apr/29/trump-fires-climate-report-contributors
Another month draws to a close allowing another monthly dot to be plotted on the global temperature record.
The daily ERA5 numbers at Climate Pulse show April’s SAT averaging +0.60ºC, down on previous months of 2025-so-far (Jan +0.79ºC, Feb +0.63ºC, Mar +0.66ºC) with Jan-Apr2025 (+0.67ºC) also lower than Jan-Apr2024 (+0.73ºC). (A plot of the daily numbers sequenced 2022-to-date is posted here – First POSTED 17th March 2025.)
This 2024-2025 comparison is what James Hansen considers to be the “acid” test for his proposal that the “bananas” temperatures of late 2023-into-2024 were “due about equally to a moderate El Nino and reduction of ship aerosols, with a smaller contribution from the present solar maximum.” Thus:-
The Jan-Apr averages using the same anomaly base as Hansen’s “1.5°C level” (1850-1900 base) run 2023 +1.29°C, 2024 +1.67°C, 2025 +1.61°C. (** The ENSO looks like its stuck on neutral for the year. Up-to-date, April’s NINO3.4 sits at -0.1ºC.)
While I am not myself convinced of Hansen’s proposed role of “reduction of ship aerosols,” I would suggest that the wibbly-wobbly global SAT is not the best data to use for this “acid test” and would suggest the 60N-60S SST (also provided by Climate Pulse) gives a better indication. That SST shows things without such large wobbles and is thus showing the level of 2025 cooling more clearly.
Thus, while the April SAT over the last 3 years run 2023 +0.32ºC, 2024 +0.67ºC, 2025 +0.60ºC (1850-1900 base +1.23°C,+1.58°C * +1.51°C), this is not very clear as to where 2025 is progressing.
Using the SST does have the wrinkle that the SST anomalies don’t readily translate to an 1850-1900 base and if it did the “1.5°C level” wouldn’t apply. But that said,the 60N-60S SST is a lot easier to meaningfully ‘eyeball’ at Climate Pulse. This shows SSTs still struggling to dip below the +0.4ºC but also it is still managing to show slow-but-on-going cooling. Thus comparing Apr2025 with previous year – 2025 +0.39ºC, 2024 +0.54ºC & 2023 +0.36ºC. And note this last 2023 anomaly would have been subject to AGW of +0.03ºC in the following 2 years although there is a strong “bananas” flavour arriving by April 2023. I would thus suggest as a better “acid test”, that 60-60 SST dropping towards +0.3ºC by the year’s-end. This measure would at least avoid objections to the 1988 & 2016 SAT comparisons having to negotiate these earlier El Niño years showing their peak temperatures respectively 8-months and 4-months later than their 2024 counterpart.
Mind, I would still not see even that “acid test” convincing me that there was a big “reduction of ship aerosols” in the “bananas.” (I should explain why.)
FYI: For those who don’t already know of it, this looks like a useful website:
“ClimaMeter is a rapid experimental framework for putting weather extremes in a climate perspective, developed by the ESTIMR team at the Laboratoire des Sciences du Climat et de l’Environnement (Institut Pierre Simon Laplace) in Paris-Saclay. ClimaMeter is led by Davide Faranda (CNRS & London Mathematical Laboratory), Mathieu Vrac (CNRS), Pascal Yiou (CEA-Saclay) & Robert Vautard (IPSL), in collaboration with Gabriele Messori (Uppsala University, Uppsala), Erika Coppola (International Centre for Theoretical Physics, Trieste) and Tommaso Alberti (Istituto Nazionale di Geofisica e Vulcanologia, Rome).
“We provide an easily interpretable contextualisation of extreme weather immediately after the actual event, as well as a more technical description and discussion of the event with a slightly longer delay.”
https://www.climameter.org/home