Zeke Hausfather

2025 was an exceptional year for the Earth's climate
⬆️ Warmest ocean heat content
⬆️ Tied as second warmest surface temps
⬆️ Second warmest troposphere
⬆️ Record high sea level and GHGs
⬇️ Record low winter Arctic ice

New State of the Climate over at Carbon Brief: https://www.carbonbrief.org/state-of-the-climate-2025-in-top-three-hottest-years-on-record-as-ocean-heat-surges/

Jan 14 at 2:58pmWeb
Show threadZeke HausfatherJan 14
Ocean heat content increased by 23 billion trillion joules, which was around 39 times greater than global primary energy use this year. This is the largest rise in OHC since 2017; overall OHC has increased by over 500 zettajoules since the 1940s.
Show threadZeke HausfatherJan 14
2025 tied with 2023 as the second warmest surface temperatures. It was nominally the second warmest in NASA and DCENT datasets, and third warmest in NOAA, Hadley, Berkeley, Copernicus, JRA-3Q, and China-MST. In all cases uncertainties overlap with 2023.
Show threadZeke HausfatherJan 14
We are including a number of additional surface temperature datasets, including DCENT (out of Harvard), the Japanese JRA-3Q reanalysis product, and the China-MST dataset. Here are the values for each, both as reported and using a common preindustrial baseline:
Show threadZeke HausfatherJan 14
Global land regions saw their second second warmest year on record at around 2C above preindustrial levels, while global oceans were the third warmest at around 1C:
Show threadZeke HausfatherJan 14
About 9% of the planet saw record warmth, an area where around 770 million people live (including 450 million people in China).
Show threadZeke HausfatherJan 14
Global surface temperatures have been exceptionally high over the past three years – well above the long-term trend the world has experienced since 1970:
Show threadZeke HausfatherJan 14
This was driven by a number of factors, including a strong El Nino event in 2023/2024, reductions in sulfur emissions from shipping and East Asia, and a stronger than expected solar cycle:
Show threadZeke HausfatherJan 14
El Nino is the single largest driver of year-to-year variability. 2024 (and to a lesser extent 2023) were boosted by a strong El Nino, while 2025 saw neutral to modest La Nina conditions:
Show threadZeke HausfatherJan 14
If we remove the effect of El Nino and La Nina from the surface temperature record, 2025 would have been the warmest year on record. The switch from El Nino in 2024 to La Nina in 2025 essentially explains all the difference in temperature between the years:
Show threadZeke HausfatherJan 14
At the end of 2024 a number of groups (Gavin Schmidt at NASA, the UK Met Office, Berkeley Earth, and Carbon Brief) provided estimates of where 2025 would likely end up. This time around we did pretty well, with the Met Office estimate ending up spot on:
Show threadZeke HausfatherJan 14
Turning to climate models, 2025 was more or less dead on the CMIP6 multimodel mean (the latest generation of models featured in the IPCC AR6 report):
Show threadZeke HausfatherJan 14
The IPCC also provided their own assessed warming projections (which effectively down-weight some very high climate sensitivity models). Compared to these observations are a tad on the high end but still broadly within the model range:
Show threadZeke HausfatherJan 14
2025 came in as second warmest in the lower troposphere, above 2023 but below 2024. The lower troposphere generally sees a much bigger effect from El Nino and La Nina events than surface temperatures:
Show threadZeke HausfatherJan 14
Looking ahead to 2026, we expect it to end up pretty similar to 2025, at somewhere between the second and fourth warmest year on record:
Show threadZeke HausfatherJan 14
Check out the full article over at Carbon Brief for more charts and analysis covering what happened in 2025 for sea level rise, glaciers, Greenland ice loss, greenhouse gas concentrations, sea ice, and many other climate variables: https://www.carbonbrief.org/state-of-the-climate-2025-in-top-three-hottest-years-on-record-as-ocean-heat-surges/
State of the climate: 2025 in top-three hottest years on record as ocean heat surges - Carbon Brief

The year 2025 was in the top-three warmest years on record

Carbon Brief