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:

The claim by Hansen et al today that climate sensitivity is 4.8°C ± 1.2°C per doubling CO2 is just as plausible as the claim by Cropper et al four days ago that its 2.8°C ± 0.8°C.

Across hundreds of different studies, and our best estimate remains somewhere between 2C and 5C. Given all the conflicting estimates, I'd strongly advise folks against glomming onto any single new study (particularly if it informs ones priors that sensitivity is high or low). Instead, we should synthesize all the different lines of evidence: agupubs.onlinelibrary.wiley.com/doi/full/10.10…

Our 2023 Q3 State of the Climate is out over at @CarbonBrief:
⬆️ Record global temps since June
⬆️ Virtually certain to be hottest year on record
⬆️ Record-setting ocean heat content
⬆️ October on track for record warmth
⬇️ Record low Antarctic sea ice
carbonbrief.org/state-of-the-c…
The past few months were exceptionally warm for the Earth's surface, with September smashing prior records by around 0.5C (the largest margin a new monthly record has been set):

The first global temperature data is in for the full month of September. This month was, in my professional opinion as a climate scientist – absolutely gobsmackingly bananas. JRA-55 beat the prior monthly record by over 0.5C, and was around 1.8C warmer than preindutrial levels. Here are monthly absolute temperatures (compared to anomalies). This September would not have been out of place as a typical July this decade in terms of global temperatures.

This is mind boggling silly. We’ve put 2.5 trillion tons of CO2 in the atmosphere. The amount of CO2 in the atmosphere has increased by 1.1 trillion tons after being relatively stable for millennia before we started emitting. It’s hard to get more clear-cut causality.

https://twitter.com/curryja/status/1706821548588630282

If you believe temperature rather than emissions are driving atmospheric CO2 increase you quickly run into a mass balance problem. We know both the oceans and biosphere are net CO2 sinks today (we measure them!). We know atmospheric accumulation is ~half of our emissions.

Its hard to overstate just how exceptionally high global temperatures are at the moment. They have blown past anything we've previously experienced by a huge margin.

Over at The Climate Brink, we try and visualize this summer of extremes in seven charts. theclimatebrink.com/p/visualizing-…
Daily global surface temperatures over the past week have been a full 1C above the recent 1991-2020 baseline period use in the JRA-55 reanalysis dataset, or around 1.9C above preindustrial.

August 2023 shattered prior August records by ~0.3C, with temperatures at 1.68C above the 1850-1900 period.

In our August update we find that 2023 as a whole is virtually certain to be the warmest year on record, with a roughly 50% chance of reaching 1.5C berkeleyearth.org/august-2023-te…
The Earth's average temperature has been at record setting levels for June, July, and August (and roughly tied prior records in May). September seems to be keeping up the trend of exceptionally warm temperatures so far: climatereanalyzer.org/clim/t2_daily/…

One of the most important findings in the recent IPCC report is that we ultimately determine how much warming will occur.

There is likely no warming "in the pipeline" once emissions get to zero. Rather, CO2 concentrations fall and temperatures stabilize https://t.co/SQl5waLZtRcarbonbrief.org/explainer-will…
Why does this happen? As emissions fall, land and ocean carbon sinks start taking up more CO2 than we emit, as they work through a backlog of our past emissions. This causes atmospheric CO2 to fall and (all things being equal) would cause cooling. bg.copernicus.org/articles/17/29…