Zeke Hausfather

Very much an outlier: bsky.app/profile/haus...

It’s a good question! The multimodel mean has historically been used ( @climateofgavin.bsky.social might have more insight into why), but I agree that medians might be less sensitive to outliers.

I had a long plane ride back from the IPCC lead author meeting in Paris 😉

Increasing progressively only if you look at ever shorter trend periods.

If your trend starts at a local minimum it will be higher. Same reason you get higher trends if you start during a strong La Niña.

Pinatubo.

That being said, other new GSAT records like GloSAT are more or less in line with GMST records so 🤷

The models shown use GSAT. The observations are a mix of GMST (Berkeley, NASA, and NOAA) and GSAT (Copernicus ERA5) so you could use the difference between them as a proxy for GSAT uncertainty.

Comparing climate models with observations The latest generation of climate models shows too much long-term warming but better reproduces recent trends

Check out the full piece (with tons of model-observation comparison figures) over at The Climate Brink:

High rates of recent warming raise questions about if CMIP6 "hot models" are really so far off from observations. I suggest that 15 years remains a bit too short a period to draw too many conclusions, and we need more time to fully pin down current human-induced warming rates.

I suggest that looking at all possible trend periods can be more illuminating than just picking a few – albeit at the expense of being a bit more difficult to explain:

Looking back at the last 56 years (1970-present), the last 25 years, and the last 15 years, we find that recent warming is well outside the range of model projections for CMIP3 and CMIP5, but CMIP6 models tend to overestimate longer term trends.

One notable finding is that the trends over the past 15 years are more on the high-end of CMIP5 model expectations than trends were below expectations during the hiatus years. Though the end of the hiatus is a cautionary tale to not over-interpret short-term trends.

I have a new update to climate model-observation comparisons over at The Climate Brink, covering CMIP3, CMIP5, and CMIP6. Models perform well globally. The latest generation shows too much long-term warming but better reproduces recent trends: www.theclimatebrink....

Indicators of Global Climate Change 2024: annual update of key indicators of the state of the climate system and human influence Abstract. In a rapidly changing climate, evidence-based decision-making benefits from up-to-date and timely information. Here we compile monitoring datasets (published at https://doi.org/10.5281/zenodo.15639576; Smith et al., 2025a) to produce updated estimates for key indicators of the state of the climate system: net emissions of greenhouse gases and short-lived climate forcers, greenhouse gas concentrations, radiative forcing, the Earth's energy imbalance, surface temperature changes, warming attributed to human activities, the remaining carbon budget, and estimates of global temperature extremes. This year, we additionally include indicators for sea-level rise and land precipitation change. We follow methods as closely as possible to those used in the IPCC Sixth Assessment Report (AR6) Working Group One report. The indicators show that human activities are increasing the Earth's energy imbalance and driving faster sea-level rise compared to the AR6 assessment. For the 2015–2024 decade average, observed warming relative to 1850–1900 was 1.24 [1.11 to 1.35] °C, of which 1.22 [1.0 to 1.5] °C was human-induced. The 2024-observed best estimate of global surface temperature (1.52 °C) is well above the best estimate of human-caused warming (1.36 °C). However, the 2024 observed warming can still be regarded as a typical year, considering the human-induced warming level and the state of internal variability associated with the phase of El Niño and Atlantic variability. Human-induced warming has been increasing at a rate that is unprecedented in the instrumental record, reaching 0.27 [0.2–0.4] °C per decade over 2015–2024. This high rate of warming is caused by a combination of greenhouse gas emissions being at an all-time high of 53.6±5.2 Gt CO2e yr−1 over the last decade (2014–2023), as well as reductions in the strength of aerosol cooling. Despite this, there is evidence that the rate of increase in CO2 emissions over the last decade has slowed compared to the 2000s, and depending on societal choices, a continued series of these annual updates over the critical 2020s decade could track decreases or increases in the rate of the climatic changes presented here.

This (1.48C) is a bit higher than our best estimate of human-induced warming to-date (~1.4C) in the recent Forster et al paper (essd.copernicus.org/...), despite 2025 being characterized by weak La Nina conditions (which would typically push down global temps.

We now expect 2025 annual temperatures to more or less tie 2023 as the second warmest year on record in ERA5, at around 1.48C relative to preindustrial (1850-1900).

However, other surface temperature datasets (e.g. Berkeley Earth) may show a tad lower as the third warmest.

November 2025 was the third warmest November on record in ERA5 at 1.54C above preindustrial levels – below only the records set in the prior two years (2023 and 2024):

Indeed. Though at least early attempts to overtly bias models have ended well...

Consensus machines Will the AI future inadvertently recenter expertise?

LLMs are fast becoming a major source of information.

In a new piece over at The Climate Brink, I argue that LLMs are fundamentally consensus machines, and could help defragment our information ecosystem – at least if their creators do not put thumbs on the digital scale.

It’s almost like something dramatically changed after the Industrial Revolution! (figure via Ed Hawkins)

Forster and Rahmstorf doesn’t have that table in it, and they do not claim we can extrapolate the current rate of warming later in the century.

These estimates build on a broader literature of current policy estimates that I reviewed in a recent paper in Dialogues on Climate Change earlier this year: journals.sagepub.com...

These six studies show a central estimate of warming from 2.4C to 2.9C, with large climate system uncertainties due to climate sensitivity and carbon cycle feedbacks; its possible that current policy warming could be as high as 4C if we roll 6s on the proverbial climate dice.

A number of new estimates of current policy warming by 2100 have been released in recent months, including three prominent ones from UNEP, IEA, and CAT in the run-up to COP30.

I've got a new piece over at The Climate Brink digging into the details: www.theclimatebrink....

If CO2 emissions go to zero in 2050 (top), the sinks (green) will bring atmospheric CO2 back down (middle), & temperature will stabalise at ~1.7°C (bottom).

Going to zero today will keep us <1.5°C

Constant emissions leads to 2.6°C, rising rapidly thereafter.

www.nature.com/articles/s41...

Global Carbon Budget 2025 Abstract. Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere in a changing climate is critical to bette...

Published today in Earth System Science Data: The Global Carbon Budget 2025
essd.copernicus.org/preprints/es...

Small typo here: it’s falling land use emissions that have counterbalanced rising fossil emissions!

Sorry, that’s what I get from not proofreading the thread. The Carbon brief piece has it right!

Global CO2 emissions separated out into fossil and land-use change components between 1959 and 2025. Data from the Global Carbon Project. Chart by Carbon Brief.

NEW – Analysis: Fossil-fuel CO2 emissions to set new record in 2025, as land sink ‘recovers’ | @hausfath.bsky.social @pfriedling.bsky.social

Read here: buff.ly/F4rY1GP

Analysis: Fossil-fuel CO2 emissions to set new record in 2025, as land sink ‘recovers’ - Carbon Brief Carbon dioxide (CO2) emissions from fossil fuels and cement will rise around 1.1% in 2025,...

For more details, see my @carbonbrief.org article with Global Carbon Budget lead @pfriedling.bsky.social: www.carbonbrief.org/...

And the new Global Carbon Budget paper: essd.copernicus.org/...