After a modest decline over the first half of the year (and after record 2024 warmth), global temperatures are ticking back up. The past two days have been the warmest on record for this time of year in ERA5 and the highest temperature anomalies since January. With 26 days of October now reporting in ERA5, October 2025 will be the third warmest on record after 2023 and 2024.

The EPA cited my paper in their argument against the endangerment finding today. However, their point is completely backwards: my paper actually supports the EPA's 2009 range of 1.8C to 4C warming by 2100. nature.com/articles/d4158… Specifically, in our paper we argue that RCP4.5 or RCP6.0 are more realistic representations of 2100 warming under current policy than the increasingly implausible RCP8.5 scenario. But the lower of those two – RCP4.5 – gives a 2100 warming range of 1.8C to 4C!

I just published an explainer on aerosols and their role in the climate that I've been working on for the past few months! It includes both how aerosols work, how emissions have changed, and how thats driven recent warming (link below). Human-caused emissions of aerosols – tiny, light‑scattering particles produced mainly by burning fossil fuels – have long acted as an invisible brake on global warming. This is largely because they absorb or reflect incoming sunlight and influence the formation and brightness of clouds.

Check out the full Carbon Brief article here carbonbrief.org/explainer-how-…

Whenever I post about climate, skeptical folks inevitable respond with this graph. So I decided to do something radical: actually read the underling scientific paper and ask the authors.

As it turns out, it actually says the opposite of what skeptics claim. Rather than arguing against human influence on the climate, the paper makes the stark claim that "CO2 is the dominant driver of Phanerozoic climate [the past 485 million years], emphasizing the importance of this greenhouse gas in shaping Earth history."

science.org/doi/10.1126/sc…

Every wildfire starts with an ignition – downed powerlines, lightning, arson – and we can do a lot to reduce these.

But in California the number of fires has dropped while the area burned has doubled. What has changed is conditions, not ignitions: Why have conditions changed? A legacy of poor forest management has led to fuel loading (particularly in the Sierras), contributing to more destructive fires. But vegetation has also gotten much drier as fire season temperatures have warmed (+3.6F since 1980s)

I have a new paper in Dialogues on Climate Change exploring climate outcomes under current policies. I find that we are likely headed toward 2.7C by 2100 (with uncertainties from 1.9C to 3.7C), and that high end emissions scenarios have become much less likely This reflects a bit of good news; 2.7C is a lot better than the 4C that many thought we were heading for a decade ago, and reflects real progress on moving away from a 21st century dominated by coal. At the same time, its far from what is needed.

I have a new analysis over at The Climate Brink exploring how rates of warming have changed over the past century.

Post-1970, GHGs (CO2, CH4, etc.) would have led to just under 0.2C per decade, but falling aerosols (SO2) have increased that rate to 0.25C. These falling aerosols have "unmasked" of some of the warming that would have otherwise occurred due to past emissions of greenhouse gases. Its been driven by large declines in Chinese and shipping SO2 emissions over the past decade, among other contributors.

Theres been a bit of confusion lately around how the climate system response to carbon dioxide removal. While there are complexities, under realistic assumptions a ton of removal is still equal and opposite in its effects to a ton of emissions.

A thread: 1/x When we emit a ton of CO2 into the atmosphere, a bit more than half is reabsorbed by the ocean and the biosphere today (though this may change as a warming world weakens carbon sinks). Put simply, 2 tons of CO2 emissions -> 1 ton of atmospheric accumulation.

The carbon cycle has been close to equilibrium through the Holocene; we know this because we measure atmospheric CO2 concentrations in ice cores. But in the past few centuries CO2 has increased by 50%, and is now at the highest level in millions of years due to human emissions. Starting 250 years ago, we began putting lots of carbon that was buried underground for millions of years into the atmosphere. All in all we’ve emitted nearly 2 trillion tons of CO2 from fossil fuels, which is more than the total mass of the biosphere or all human structures:

We just published our State of the Climate Q2 update over at @CarbonBrief:

⬆️ Now a ~95% chance 2024 will be the warmest year on record.
⬆️ 13 month streak of records set between June 2023 and June 2024.
⬆️ July 22nd 2024 was the warmest day on record (in absolute terms).
⬇️ July 2024 will very likely come in below July 2023, breaking the record streak.
⬇️ The rest of 2024 is likely to be cooler than 2023 as El Nino fades and La Nina potentially develops.
⬇️ Second lowest Antarctic sea ice on record.carbonbrief.org/state-of-the-c… The past 13 months have each set a new record, with 2024 being quite a bit warmer than 2023 (at ~1.63C above preindustrial levels) in the ERA5 dataset:

Global surface temperatures from @BerkeleyEarth are now out for June. It was the warmest June on record for land, oceans, and the globe as a whole by a sizable margin (~0.14C), and came in at 1.6C above preindustrial levels. berkeleyearth.org/june-2024-temp…
This was the 13th consecutive record setting month, and the 12th month in a row above 1.5C:

Global temperatures were extremely hot in June 2024, at just over 1.5C, beating June 2023's previous record-setting temperatures by 0.14C and coming in around 0.4C warmer than 2016 (the last major El Nino event).

Now 2024 is very likely to beat 2023 as the warmest year on record June 2024 was so warm that – in the absence of 2023's exceptional warmth – it would have beaten any past July as the warmest absolute monthly temperature experienced by the planet in the historical record:

We’ve long talked about the carbon budget, but given that the world is on track to pass the 1.5C target in the coming decade its time to start talking about the "carbon debt".

My latest piece over at The Climate Brink: theclimatebrink.com/p/the-growing-… Carbon dioxide accumulates in the atmosphere where it lasts for an extremely long time. While about half of our emissions are removed by land and ocean carbon sinks over the first century, it takes on the order of 400,000 years for nature to fully remove a ton of CO2.

Recently we've seen a vibrant debate on when the world will firmly pass 1.5C.

Over at @CarbonBrief I weigh in with a new analysis, finding that it will most likely occur in the late 2020s or early 2030s in a world where emissions do not rapidly decrease. carbonbrief.org/analysis-what-…
Global temperatures in any given year reflect short-term natural variability on top of longer-term human-driven warming. For example, a big El Niño or La Niña event can result in global temperatures up to 0.2C warmer or cooler, respectively, than they would otherwise be.

There is something of a genre of very online individuals™ discovering stratospheric aerosol injection and proclaiming it as a low-cost solution to climate change. Spoiler alert: its not.

In this case the thread uses a bunch of my figures so its worth responding.

https://twitter.com/cremieuxrecueil/status/1794231057815867807

Climate change is driven primarily by our emissions of carbon dioxide. We've emitted a lot of CO2: around 2.5 trillion tons since 1750, or the weight of the the biosphere and everything humans have ever built combined theclimatebrink.com/p/the-staggeri…

The first quarter of the year is off to an exceptionally warm start, as I discuss in a new Q1 State of the Climate Report over at @CarbonBrief:
⬆️ Warmest Jan, Feb, March, and April (to date) by ~0.1C
⬆️ 2024 on track to be warmest or second warmest year carbonbrief.org/state-of-the-c…
Based on first three months of the year and the current El Nino / La Nina forecast, we expect 2024 to be similar to or slightly warmer than 2023. With only 3 months in we can't know precisely where the year will end up, but its virtually certain to be at least the 2nd warmest:

The rate of warming has increased notably over the past 15 years. This is not just natural variability – there is increasing evidence that the world is now warming faster than it has since 1970.

However, this should not come as a surprise; acceleration is exactly what our models expect: carbonbrief.org/factcheck-why-… In a new piece over at @CarbonBrief I compare observed warming (and its historic rate) to three different future projections:
1) The IPCC AR6 assessed warming (SSP2-4.5)
2) The full CMIP6 ensemble (SSP2-4.5)
3) Hansen et al 2023's projected acceleration.

February 2024 was the warmest February on record in the ERA5 dataset, at around 1.79C above preindustrial records.

It beat the prior record set during the 2016 super-El Nino by 0.12C: pulse.climate.copernicus.eu
It wasn't only the warmest February on record – this past month saw the largest anomaly (change from the 1850-1900 preindustrial baseline) at 1.79C of any month on record, beating out December (1.77C) and September (1.73C) 2023.

The past 12 months are 1.56C above preindustrial.

Despite today's grim milestone with the world passing 1.5C over the past 12 months, I see some reasons for cautious climate hope.

We stand both on the brink of severe climate impacts, but also on the brink of a rapid energy transition away from fossil fuels. A decade ago global emissions were skyrocketing, and many thought we were heading toward a particularly dark climate future where the 21st century would be dominated by coal and global emissions would double or triple by 2100.

I've been working over the past year on a promising new pathway to remove carbon from the atmosphere: Enhanced Rock Weathering.

With today's $57 million offtake agreement with @LithosCarbon the approach has gone mainstream:

A thread on the science:frontierclimate.com/writing/lithos Over geologic time the amount of carbon in the atmosphere is determined largely by the balance of volcanism and weathering of silicate rocks (which largely come from volcanoes!).

Today around a billion tons of CO2 is removed from the atmosphere annually by natural weathering.

Global temperatures in October smashed the prior monthly record by 0.4C, and were ~1.7C above preindustrial levels.

It wasn't quite as gobsmacking as September, but still comes in as the second most anomalous month in what has been an exceptionally hot year already. Here is a comparison of October 2023 compared to all prior Octobers in the two leading reanalysis products: ERA5 and JRA-55. Note that HadCRUT5 is used here to help estimate warming since preindustrial: