UNEP's route back to 1.5C rests on removing 10 gigatonnes of CO2 a year
UNEP now accepts the overshoot and describes a way back to 1.5C by 2100 that needs global emissions halved by 2035 and then removal running at a scale one outside researcher puts at 100,000 times today's.
The Scientist · Science desk
What happened
- A UNEP report acknowledges the world is likely to pass 1.5C of warming within the next few years, while maintaining that cooling the planet back to that level by the end of the century remains possible.
- Nature reports that on the planet's current emissions trajectory, the best outcome the report sees for this century is warming of about 1.8C above pre-industrial levels.
- The return scenario runs on carbon dioxide removal of around 10 gigatonnes a year beyond net zero, set against current global emissions of roughly 40 gigatonnes a year.
- Report author Joeri Rogelj of Imperial College London says holding warming to 1.8C would require global emissions to be halved by 2035.
- Konstantin Weber at ETH Zurich says only two scenarios in the latest set prepared for climate modellers imply a return to 1.5C before 2150.
Why it matters
- What it limits constraint The removal side of the pathway is a procurement problem before it is a science problem: the cheap option is capped by available land, and the option that can scale is the expensive one, so someone has to fund gigatonne-scale capture for decades.
- Who has to decide decision Adaptation planners are being handed two different design numbers, the report's 1.8C return path and Knutti's advice to build for at least 2C, and long-lived infrastructure cannot be sized to both.
- What doesn't add up contradiction Nature presents about 1.8C as the ceiling of current-trajectory hope while Weber's current-policies scenario lands near 3C by 2100, and which of those you adopt changes what overshoot adaptation is actually preparing for.
- What it sets up precedent Geden's concern is institutional rather than physical: once overshoot-and-return becomes the official fallback, further delay can be absorbed into a longer return date without any goal formally being missed.
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Start with the removal number, because it is what carries the scenario. Around 10 gigatonnes of CO2 taken out of the air each year is a quarter of the roughly 40 gigatonnes the world emits now [5][18], and it is required after residual emissions from sources like farming have already been balanced out, not instead of that [5]. Reto Knutti at ETH Zurich, who did not work on the report, puts the necessary scale-up at a factor of about 100,000 [6]. Run the factor backwards and the implied base is roughly 100,000 tonnes a year: ten gigatonnes is ten billion tonnes, divided by 100,000 [19]. What the factor does not tell you is which methods sit in that denominator, which matters because Knutti's point is that the cheap method and the scalable method are not the same one. Planting forests is cheap and runs out of land; direct air capture can scale and is, in his words, really expensive [7].
The emissions half of the pathway is no gentler. Halving global emissions by 2035 [9] means going from about 40 gigatonnes to about 20, which leaves the 10 gigatonnes of net-negative removal at half the size of what would still be there to cancel [20]. New Scientist points out that emissions are still rising worldwide [22].
What makes the return conditional rather than merely expensive is the peak. Debra Roberts of the University of KwaZulu-Natal, one of the report's authors, says a return depends on warming staying under 1.8C, because past that the irreversible changes begin to cascade and the job gets much harder [3]. Nature reads that same 1.8C differently, as the best this century can deliver on the current trajectory [2]. Konstantin Weber at ETH Zurich notes that the current-policies scenario in the latest modelling set points to about 3C by 2100 [21].
The honest description, then, is that overshoot-and-return is arithmetically available and, in Knutti's assessment, technically and financially possible but not politically plausible; his advice to policymakers is to plan adaptation for at least 2C, if not more [15][16]. James Dyke at the University of Exeter goes further, saying there are still no credible plans for large-scale carbon dioxide removal and that societies should prepare for a warmer, more dangerous world that could persist for centuries [10]. Oliver Geden, who has watched the concept move from thought experiment toward official plan B, says it may amount to a way of masking ongoing failure [11].
Inger Andersen of UNEP describes the new posture as approaching 1.5C differently, from above [4]. That framing does real work: it keeps a number nearly 200 Paris signatories adopted in 2015 [8] and that the IPCC ties to tipping-point risk growing with every tenth of a degree [13]. It also has a limit Roberts states plainly, which is that arriving back at 1.5C is not arriving back at the world that existed at 1.5C, because some of the losses in between do not reverse [12].
What to watch
- Whether the next round of national pledges contains anything resembling a halving of global emissions by 2035, or whether the annual total keeps rising.
- Whether modelling groups add scenarios that come back below 1.5C before 2150, a set that currently numbers two.
- Whether COP language moves from keeping 1.5C in reach toward explicit overshoot-and-return wording, after last year's Brazil resolution.
Clarity's read
What the record supports and how the coverage leans. The claims behind it follow.
Reality
- Evidence62
- Adoption6
- Hype gap+45
- Incentives50
- Confidence60
Perspective Coverage
5 publishers- Builder
- Builder 28%
- Operator
- Operator 53%
- Investor
- Investor 19%
Claim ledger
Ranked by verification strength, evidence, and original report placement.
- [1]
A report by the UN Environment Programme acknowledges that the world is likely to overshoot 1.5C of warming within the next few years, but says it is still possible to cool the planet back down to that level by the end of the century.
- [2]
According to Nature, the UNEP report finds that the best the planet can hope for on its current emissions trajectory is warming of about 1.8C above pre-industrial levels this century.
- [3]
Report author Debra Roberts of the University of KwaZulu-Natal says achieving a return to 1.5C would require limiting temperature rises to no more than 1.8C, because beyond that there will be cascading effects from irreversible changes that make it much harder.
- [4]
Inger Andersen of UNEP: "Even if we exceed 1.5, let's be very clear: that 1.5 target is still the goal. But now we need to approach it differently, from above."
- [5]
The report's return scenario requires carbon removal beyond net zero of around 10 gigatonnes of CO2 each year, over and above balancing hard-to-tackle sources such as farming, compared with current emissions of around 40 gigatonnes.
- [6]
Reto Knutti at ETH Zurich, who was not involved in the report, says the scenario means scaling up carbon removal by a factor of around 100,000.
- [7]
Knutti says cheap forms of carbon removal such as planting forests cannot be scaled up that far because there is not enough land, while direct air capture could be scaled up but is really expensive.
- [8]
The nearly 200 countries that signed the Paris climate accord in 2015 agreed to keep the rise in global average temperatures well below 2C relative to the pre-industrial average, with a stretch goal of 1.5C.
- [9]
Report author Joeri Rogelj at Imperial College London says restricting warming to 1.8C requires a halving of global emissions by 2035.
- [10]
James Dyke at the University of Exeter says there are still no credible plans for large-scale carbon dioxide removal, and that human societies must adapt and prepare for a warmer and more dangerous world that will persist potentially for centuries.
- [11]
Oliver Geden of the German Institute for International and Security Affairs says overshooting and returning to 1.5C was until recently no more than a scientific thought experiment and could now become the official plan B, and that the overshoot concept may turn out to be no more than a way to mask ongoing failure.
- [12]
Roberts says some losses will be irreversible, which means returning to 1.5C does not mean returning to the same world we left.
- [13]
According to the IPCC, beyond the 1.5C threshold the risks of triggering dangerous tipping points in the climate system grow more acute, and rise with every tenth of a degree of warming beyond that point.
- [14]
The 2021 UN climate summit in Glasgow was themed "keep 1.5C alive", and last year's UN climate meeting in Brazil ended with a resolution to keep 1.5C in reach.
- [15]
Knutti thinks achieving the removal scale-up is technically and financially possible, but not politically plausible, and says policymakers and the public should be told this is not the thing to plan for.
- [16]
Knutti says the plan should be to adapt for at least 2 degrees of warming, if not more.
- [17]
Konstantin Weber at ETH Zurich says that among the latest emissions scenarios that will be used by climate modellers, only two imply a return to 1.5C before 2150.
- [18]
Removing 10 gigatonnes of CO2 a year equals 25 per cent of current global emissions of about 40 gigatonnes a year.
- [19]
A 100,000-fold scale-up ending at 10 gigatonnes a year implies a starting point of about 100,000 tonnes of CO2 removal a year.
- [20]
Halving emissions of about 40 gigatonnes by 2035 leaves roughly 20 gigatonnes a year, so the 10 gigatonnes of net-negative removal is about half the size of the residual emissions still to be cancelled.
- [21]
Weber says the scenario based on current policies forecasts warming of around 3C by 2100.
- [22]
New Scientist judges the halving of emissions by 2035 highly unlikely given that emissions are still rising worldwide.
Sources
5 independent publishers whose own reporting we read for this story.
- eos.orgThe World Will Overshoot 1.5°C and Must Now Remove Carbon, United Nations Says
1 article · September 2, 2026
- nature.comUN finally admits global warming will shoot past 1.5 ºC climate limit
1 article · September 1, 2026
- newscientist.comCan we really reverse global warming after overshooting 1.5°C?
1 article · September 1, 2026
- phys.orgGlobal warming will exceed limit, UN says in a report that maps path to get back below danger zone
4 articles · September 2, 2026
- scientificamerican.comU.N. admits exceeding Paris Agreement’s 1.5-degree-C warming target is “unavoidable”
1 article · September 2, 2026
Topics and entities
Topics
- Climate Tipping Points
- 1.5C overshoot and return
- Carbon Dioxide Removal
- Climate Adaptation