The Earth is on a “disastrous trajectory” with “no adequate global governance” to deal with the scale of threats posed by climate tipping points, warns a major new report.
These tipping points “pose some of the gravest threats faced by humanity”, according to the authors.
They identify more than 25 tipping points across the Earth system, ranging from ice-sheet collapse to rainforest dieback.
“Five major tipping points are already at risk of being crossed due to warming right now and three more are threatened in the 2030s as the world exceeds 1.5C global warming,” the report finds.
Crossing Earth system tipping points would have “catastrophic” impacts on societies, with the potential to “escalate violent conflicts, mass displacement and financial instability”, the report also warns.
The authors say that promoting “positive social tipping points” in socio-behavioural, technological, economic and political systems is “the only realistic systemic risk governance option” to limit the risks.
Many positive tipping points have already been crossed – such as renewable energy becoming the cheapest form of electricity in some countries, and electric vehicles gaining the largest share of the market in others – the report finds.
An international team of more than 200 researchers have contributed to this report, which was initiated at a conference on tipping points in September 2022. (See Carbon Brief’s coverage of the event.) The report was funded by the Bezos Earth Fund.
The authors of the report support a proposal – currently under consideration – for the Intergovernmental Panel on Climate Change (IPCC) to prepare a special report on the topic of tipping points.
They also call for the risks and opportunities around tipping points to be included in the global stocktake of progress towards the goals of the Paris Agreement, as well as future revisions of Nationally Determined Contributions and national and sub-national policy measures.
In this Q&A, Carbon Brief unpacks the report’s findings on “negative” Earth system tipping points and “positive” social tipping points.
- What are tipping points?
- What are the main Earth system tipping points?
- When could key thresholds be crossed?
- What are the impacts of crossing tipping points?
- Can ‘positive tipping points’ mitigate the risks?
What are tipping points?
Scientists have warned for decades that many Earth systems are at risk of crossing “tipping points” – critical thresholds that, if exceeded, could push a system into an entirely new state.
Prof Tim Lenton is the chair of climate change and Earth system science at the University of Exeter and lead author of the new report on “global tipping points”. He describes a tipping point as a system in which “a small change makes a big difference and changes the state or the fate of a system”.
The report uses the analogy of a ball in a valley to describe tipping points, as shown in the graphic below.
In the left-most panel (blue), the ball sits in the left-side valley. If the ball is given a small push, it rolls briefly up the side of the valley before returning to its starting position. This “resilience” – the system’s ability to withstand changes – shows that the system is stable, the report says.
However, the report warns that human activity – including climate change, ecosystem degradation and pollution – are making many Earth systems less stable. This is shown by the left-hand valley getting shallower in the middle panel (purple) and the lowering of the hill between it and the right-hand valley. Now it would be easier for the ball to move into the right-hand valley when pushed.
As a system comes close to a tipping point, it may be slower to return to its original state after a “perturbation” or disturbance, the report says. This would be shown by the ball returning more slowly to its original position after it is pushed.
Dr David McKay – an independent research consultant and visiting fellow at the University of Exeter’s Global Systems Institute – is a section lead on the new report. He describes this behaviour as a “wobble” and tells a press briefing that it can often be picked up using observational data. This is important, because it can provide an early warning signal that a tipping point is approaching.
A “tipping point” is crossed when the ball rolls past the point of no return into the right-side valley, leaving its original state and settling into a new stable state. This is shown in the right-hand panel (red). It is now very difficult for the ball to return to its original state in the left-hand valley.
The report says that a tipping point occurs “when change in part of a system becomes self-perpetuating beyond a threshold, leading to substantial, widespread, frequently abrupt and often irreversible impact”.
Under this definition, it is also possible for tipping points to be reversible and “non-abrupt” – although this is not usually the case, the authors note.
What are the main Earth system tipping points?
In recent years, there has been plenty of academic discussion about which elements of the Earth system might exhibit tipping points.
The report synthesises hundreds of peer-reviewed articles to identify more than 25 parts of the Earth system that have tipping points across the cryosphere, biosphere, atmosphere and oceans. (Carbon Brief has previously unpacked nine of them in detail.)
Importantly, the authors also show which systems they do not believe to exhibit tipping behaviour.
Cryosphere
The report identifies multiple tipping points in the cryosphere, as shown on the map below.
The colours and markers indicate how confident the authors are that each system has a tipping point. A red bar and “+++” marker indicates that the authors are very confident that the system is a tipping point. A blue bar and “- – -” marker indicates that the authors are very confident that the system is not a tipping point. The four arrows and globe symbols indicate regional and global systems, respectively.
There are “multiple lines of evidence” to support the existence of “large-scale” tipping points from the melting of the Greenland and Antarctic ice sheets, the report says, explaining that if ice loss exceeds a threshold amount, self-amplifying feedbacks could cause the ice to disintegrate even faster, leading to large-scale ice-sheet “collapse”.
Conversely, the authors have “high confidence” that Arctic summer sea ice loss is not a tipping system, finding that in models and observations, summer sea ice loss tends to increase “gradually, but surely” in line with warming.
Meanwhile, the authors find evidence for “localised and regional” tipping points in glaciers and permafrost, but find that these systems do not exhibit “large-scale tipping dynamics”.
Oceans and atmosphere
There are four further tipping points in the oceans and atmosphere, including monsoons over west Africa, India and South America, clouds and El Niño southern oscillation (ENSO), according to the report. These are shown in the map below.
The Atlantic Meridional Overturning Circulation (AMOC) is a major system of ocean currents that plays an important role in regulating the global climate. The report explains that rising temperatures, combined with an influx of cold, fresh water from the melting of the Greenland ice sheet, could destabilise these ocean currents, potentially causing the entire system to “shut down”.
Similarly, the authors find evidence for tipping points in the overturning circulations in the Atlantic and the Southern oceans, as well as for the west African monsoon.
The authors also assess the literature on cloud-induced tipping points. Various different mechanisms linked to incoming solar radiation and outgoing infrared radiation have been suggested, but the authors conclude that “concern about cloud-driven tipping points is relatively low”.
Biosphere
The report finds the most tipping points in the biosphere, as shown in the map below. Different colours of shading indicate different biomes – for example, coral reefs in red and mangroves in pink.
Systems in the biosphere have more “co-drivers” that can reduce their resilience – such as climate change, habitat loss and pollution – making tipping points easier to reach, the report finds.
For example, it notes that the Amazon provides much of its own rainfall by cycling water between the atmosphere and vegetation. Deforestation and climate change can disrupt this mechanism, pushing the system over a tipping point where it turns from forest into savannah. This process is called forest “dieback”.
Among tropical forests, there is most evidence of a tipping point for the Amazon, the report finds. Other tropical forests such as the Congo have evidence for local tipping points, but are less likely to cross them, the report finds.
The authors also find that mangroves and sea grasses – which are “historically among the most human-threatened ecosystems in the world” – are at risk tipping regionally. They highlight regional examples of “mangrove die-off”, which typically occur when the mangroves are “physiologically stressed”.
The report also looks at marine food webs and fisheries, finding that “marine community shifts take place when abrupt changes cascade through several species or functional groups of an ecosystem”.
When could key thresholds be crossed?
Assessing when key climate tipping points may be crossed has been a key area of research for many years. One way to identify imminent tipping points is by looking for the “wobble” or “loss of resistance” in a system.
For example, the report cites research that finds three-quarters of the Amazon rainforest has lost “resilience” since 2003, making it slower to recover from droughts and heatwaves. This indicates that the forest could be approaching a tipping point, the authors say.
Parts of the Greenland ice sheet and AMOC are also exhibiting a loss of resilience, the report finds. It adds that given present-day warming of 1.2C, tipping of warm-water coral reefs is likely:
“Coral reefs are already experiencing tipping points, as more frequent warming-driven bleaching events, along with pollution, extreme weather events and diseases, tip them to degraded algae-dominated states.”
As the planet continues to warm, the likelihood of crossing key thresholds increases. The report also draws on research recently published by McKay, which assesses how many tipping points could be triggered at different levels of global warming.
The upper half of the plot below shows the likelihood of triggering 15 tipping elements at different temperature levels. Yellow indicates a low likelihood and red indicates a high likelihood, while the dotted line indicates a central estimate.
The grey line underneath shows observed warming to the present day and projections out to 2100 from 1.5C (green) to more than 4C (red). The grey shading in the upper chart indicates expected warming given current climate policies.
The report says that five different tipping points are already “at risk of being crossed due to warming right now”. These are Greenland and West Antarctic ice sheet collapse, warm-water coral reef die-off, widespread localised abrupt thaw in permafrost and overturning circulation collapse in the North Atlantic subpolar gyre.
The North Atlantic subpolar gyre is a counter-clockwise ocean current to the south of Greenland, which drives the oceanic currents and redistributes heat and freshwater in the high latitude North Atlantic. The gyre is a component of AMOC, and is considered as a major tipping element of the climate system.
The report adds that three more tipping points are at risk of being crossed in the 2030s as the world exceeds 1.5C above pre-industrial temperatures.
However, the report warns that key thresholds could be crossed “at lower levels of global warming than previously thought”, adding:
“Our best models likely underestimate tipping point risks. The world is largely flying blind into this vast threat.”
This underestimation is largely due to “patchy and fragmented” knowledge, the authors say. For example, they note that “typical modelling approaches struggle to accurately represent ice sheet dynamics”.
The authors of the report support a proposal for the IPCC to prepare a special report on the topic of tipping points. The proposal was put forward by Switzerland in May 2022 and is currently under consideration.
What are the impacts of crossing tipping points?
The impacts of crossing Earth system tipping points “could be catastrophic”, the report warns.
Melting of the Greenland and Antarctic ice sheets would endanger coastal communities, and could lead to the complete loss of many small island nations, the report finds. Antarctic ice sheet instability alone could lead to a potential sea level rise of two metres by 2100, exposing 480 million people to annual coastal flooding events, it says.
Amazon dieback would be a “catastrophe for biodiversity”, the report finds. Reduced river flow would lead to transport difficulties in the region, and some six million people would face “extreme heat stress risk”. Overall, the report estimates that a complete Amazon dieback would cause damages of between $1tn and $3.5tn.
Thawing permafrost causes the ground to become unstable or “slump”, and the report warns that 70% of current infrastructure in permafrost regions is in areas with “high potential for thaw by 2050”.
It adds that crossing a tipping point in the AMOC would lead to global changes in rainfall patterns, with implications for water security and crop production around the world. The warm water that the AMOC carries northwards releases heat into the atmosphere, which means it plays a crucial role in keeping Western Europe warm.
However, the Earth system tipping points do not act in isolation. The authors find that crossing some tipping points, such as the dieback of rainforests or thawing of permafrost, releases more CO2 into the atmosphere, causing further warming.
Furthermore, many Earth systems are interlinked, meaning that crossing one tipping point can increase the likelihood of crossing others. The authors describe this as a “domino effect” or “tipping cascade”.
The map below shows these interactions. Red arrows indicate that crossing one tipping point causes another system to become more unstable, making it more likely to tip. Blue arrows indicate the opposite. Grey arrows indicate unclear effects.
Systems that may not tip on their own – but are still important due to their interactions with other systems – are shown with a blue outer circle. Tipping systems that exert a notable feedback on global average temperature when they tip are denoted by a red inner ring.
The report finds that the majority of interactions between climate tipping systems are destabilising – indicating that crossing one tipping point will generally lead to further tipping points being crossed.
For example, disintegration of the Greenland ice sheet would result in large volumes of cool freshwater flowing into the ocean, which could push the AMOC beyond a tipping point. This, in turn, could lead to an intensification of ENSO, which could go on to influence weather patterns over the Amazon, causing rainforest dieback, the report explains.
Crossing key tipping points “could have catastrophic impacts on human societies”, including an increase in violence and conflict, large-scale displacement and financial destabilisation, the authors warn.
The report says that Earth system destabilisation could lead to “social cohesion breaking down”, driving an increase in “mental disorders”, as well as “greater radicalisation of various groups and polarisation, making it harder to find collective solutions”. The report adds:
“These impacts could escalate to threaten the breakdown of economic, social and political systems, triggering destructive tipping points in societies experiencing stresses beyond their ability to cope.”
The authors add that each time a tipping point is crossed, humanity will be forced to divert more attention and resources into disaster response, “eroding away some of our agency
to tackle the underlying drivers”. This in turn would make it more likely for more tipping points to be crossed in the future, creating a “vicious cycle”, they say.
Can ‘positive tipping points’ mitigate the risks?
“The existence of tipping points means that ‘business as usual’ is now over,” the report warns. It adds:
“Rapid changes to nature and society are occurring, and more are coming. If we don’t revise our governance approach, these changes could overwhelm societies as the natural world rapidly comes apart.”
However, the authors add that “currently, there is no adequate global governance at the scale of the threats posed by negative tipping points”.
The authors argue that “positive social tipping points” – feedbacks in socio-behavioural, technological, economic and political systems that trigger a positive change – could be “the only realistic systemic risk governance option” to limit the risks.
Lenton told the press briefing that humanity has “left it basically too late for incremental action on the climate crisis”, adding that positive tipping points are key to limiting dangerous levels of warming.
Many positive social tipping points are being reached or have already been crossed, the authors say.
For example, they say that renewable energy has reached a tipping point of cost parity with fossil-fuelled power generation. They add that electric vehicles “show evidence of passing or approaching tipping points in major markets including China and Europe”.
Dr Tom Powell – a research impact fellow at Exeter’s Global Systems Institute and section lead on the report – told the press briefing that “the more of something we build, the cheaper it gets to build”.
He called this a “powerful reinforcing feedback”, adding that it is responsible for some of those cost reductions and renewable energies and electric vehicles.
In a similar way to negative Earth system tipping points, one positive social tipping point can trigger another, leading to a domino or cascade that generates “widespread societal change”, the authors say. Lenton outlined a positive tipping cascade in electric vehicle manufacture:
“As electric vehicles pass the positive tipping point of market dominance, this produces lots of cheap batteries, and those low cost batteries are crucial to provide essential storage capacity to reinforce a different positive tipping point towards renewable energy for our power supply.
“And that can in turn trigger positive tipping points in producing green ammonia and green hydrogen fuels for fertiliser, shipping and so on.”
Powell adds that “social contagion is a really powerful force”, noting that “the more people around you who are adopting sustainable choices, the more likely you are to do so yourself”. He adds:
“The more visible sustainable choices are among the general population, the easier it becomes for politicians to make policy choices that might have seemed very difficult a few years ago.”
However, positive social tipping points “don’t just happen by magic”, Lenton told the press briefing. Instead, he said they need “coordinated action”.
The report’s authors call for Earth system tipping point risks, corresponding action and positive tipping point opportunities to be included in the global stocktake under the Paris Agreement, as well as future revisions of Nationally Determined Contributions (NDCs) and national and sub-national policy measures.
The most recent iteration of the global stocktake text mentions climate tipping points twice. In one, it invites the scientific community to:
“Generate information relevant for NDCs and aligning them with 1.5C, cross-cutting considerations such as tipping points, guidance on risks and impacts, vulnerability, cryosphere and closing observation gaps.”
Dr Manjana Milkoreit – a postdoctoral fellow at the University of Oslo and section lead on the report – adds that decisions and actions taken in the coming decades will commit us to “really long-term changes”, adding that the issue of tipping points is important for our notions of intergenerational justice.
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Q&A: Climate tipping points have put Earth on ‘disastrous trajectory’, says new report
Among a flurry of posts on social media last weekend, US president Donald Trump declared “good riddance” to a specific emissions scenario used in global climate projections.
The “RCP8.5” scenario, which envisages a future of very high carbon emissions, was “wrong, wrong, wrong”, the president wrote in block capitals.
This was “just admitted” by the UN’s “top climate committee”, he falsely claimed, referring to the Intergovernmental Panel on Climate Change (IPCC).
The post was quickly picked up by right-leaning media, amplifying Trump’s misrepresentation of emissions scenarios and the role of the IPCC.
His claim follows the publication of a new set of emissions scenarios that will feed into the next IPCC reports.
While the new scenarios no longer include such high emissions as in RCP8.5, they also show it is “not possible” to limit global warming to 1.5C above pre-industrial levels without significant “overshoot”, one of the authors tells Carbon Brief.
Moreover, projections suggest that the world is still on course for between 2.5C and 3C of warming, another author says.
This level of warming was previously described as “catastrophic” by the UN.
In this factcheck, Carbon Brief looks at Trump’s comments, the debate around RCP8.5 and the “good” and “bad” news within the latest scenarios.
- What did Trump say?
- What is RCP8.5?
- Why is RCP8.5 so hotly debated?
- How has RCP8.5 been replaced?
- How is the IPCC involved?
What did Trump say?
In the late evening of Saturday 16 May, Trump posted the following message on his Truth Social social-media platform:
“Dumocrats” is a derogatory nickname for Democrat politicians, debuted by the president in a televised Fox News interview on Thursday 14 May, according to the Independent.
By “top climate committee”, the president was presumably referring to the IPCC, the UN body responsible for assessing science about human-caused climate change.
However, the IPCC does not develop, control or own climate scenarios. Moreover, it has not published anything stating that any climate scenario is “wrong”. (For more, see: How is the IPCC involved?)
Nevertheless, right-leaning media outlets have reported on Trump’s comments, in many instances repeating his false assertion that the RCP8.5 climate scenario had been developed by the IPCC.
The New York Post misleadingly claimed that the IPCC “had quietly adjusted” its framework of emission scenarios. The Daily Caller, a pro-Trump conspiratorial US outlet, adds its own falsehoods stating that “IPCC researchers revised their modelling approach last month, swapping the extreme pathway for seven alternative scenarios”. The climate-sceptic Australian claimed that scientists had “quietly scrapped the apocalyptic forecasts that have terrified policymakers and the public”.
With Fox News also covering Trump’s comments, along with an earlier article by the Times, much of the reporting around RCP8.5 in recent days has been driven by media controlled by the climate-sceptic mogul Rupert Murdoch.
It is not the first time the Trump administration has attacked RCP8.5. In an executive order issued in May 2025 – entitled, “Restoring gold-standard science” – the White House included the climate scenario in a list of examples of how the previous government had “used or promoted scientific information in a highly misleading manner”.
Federal agencies, it claimed, had been using RCP8.5 to “assess the potential effects of climate change in a higher warming scenario”, despite scientists warning that “presenting RCP8.5 as a likely outcome is misleading”.
The executive order came after Project 2025 – a policy wishlist for Trump’s second term published in 2023 by the Heritage Foundation, an influential rightwing, climate-sceptic thinktank in the US – criticised the climate scenario.
The manifesto said a “day-one” priority for the new government should be to “eliminate” the US Environmental Protection Agency’s “use of unauthorised regulatory inputs”, such as “unrealistic climate scenarios, including those based on RCP8.5”.
What is RCP8.5?
Scientists use emissions scenarios to explore potential future climates, based on how global energy and land use could change in the decades to come.
These scenarios are not predictions or forecasts of what will happen in the future. Therefore, Trump’s declaration that projections under RCP8.5 were “wrong, wrong, wrong” misrepresents the purpose of emissions scenarios.
Different modelling groups have produced thousands of different scenarios over the years. RCP8.5 was developed by scientists back in the early 2010s as one of a set of four consistent “representative concentration pathways”, or RCPs, for climate modellers to use.
As their name suggests, the RCPs were representative of the vast array of scenarios in the scientific literature.
Their corresponding numbers – 2.6, 4.5, 6.0 and 8.5 – do not describe temperature rise (as some mistakenly assume), but the level of “radiative forcing” that each pathway reaches by 2100. This forcing level is a measure of the change in the Earth’s “energy balance” (in watts per square metre) caused by human-caused greenhouse gas emissions.
As the highest forcing of the set, RCP8.5 was a scenario of very high emissions and extensive global warming.
When it was originally published in 2011, RCP8.5 was intended to reflect the high end – roughly the 90th percentile – of the baseline scenarios available in the scientific literature at the time.
A “baseline” scenario is one that assumes no climate mitigation, explains Dr Chris Smith, senior research scholar at the International Institute for Applied Systems Analysis (IIASA) in Austria. He tells Carbon Brief:
“RCP8.5 was developed as a no-climate-policy scenario, often called ‘reference’ or ‘baseline’ scenarios. These are used to benchmark the actions of climate policy.”
Under RCP8.5, the IPCC’s fifth assessment report (AR5) in 2013 projected a best estimate of 4.3C of temperature rise by 2081-2100, compared to the pre-industrial period, with a “likely” range of 3.2C to 5.4C.
The RCPs were succeeded in 2017 by the “shared socioeconomic pathways”, or SSPs. The SSPs included a set of five socioeconomic “narratives”, which described factors such as population change, economic growth and the rate of technological development.
The SSPs were then used in the IPCC’s sixth assessment (AR6) cycle, which ran over 2015-23. The upper end of the AR6 temperature projections was provided by the successor to RCP8.5, known as SSP5-8.5, which indicated warming of 4.4C by 2081-2100, with a “very likely” range of 3.3C to 5.7C.
Why is RCP8.5 so hotly debated?
Prof Detlef van Vuuren from Utrecht University, a leading figure in the development of emissions scenarios for many years, tells Carbon Brief that RCP8.5 is a “low-probability, high-risk scenario and it was always meant like that”.
The scenario assumed a world without climate policy and was designed to explore the consequences of high levels of greenhouse gases and global warming. It was not, van Vueren says, a “best-guess scenario” of what the future held in store.
However, in some research papers, RCP8.5 was characterised as “business as usual”, suggesting that it was the likely outcome if society did not pursue climate action.
This was “incorrect”, says van Vuuren, noting that RCP8.5 “is not a likely outcome”. He adds: “It’s never been a likely outcome.”
Over time, RCP8.5 became hotly debated in academic circles, with some scientists arguing that such high emissions were becoming increasingly unlikely and others claiming that RCP8.5 was still consistent with historical cumulative carbon dioxide (CO2) emissions.
Carbon Brief unpacked the arguments in this debate in a detailed explainer in 2019.
The charts below, originally included in a 2012 Nature commentary and then updated each year by the authors, shows how projected CO2 emissions under RCP8.5 (red line) compares with the other RCPs (bold coloured lines) and observations (black line).
The left-hand chart shows total CO2 emissions, including land-use change, while the right-hand chart shows CO2 emissions from burning fossil fuels and producing cement – the dominant drivers of 21st century emissions.
While emission trends up to the early 2010s approximately tracked RCP8.5, a flattening of emissions growth in the years since has meant they have not kept pace with the sustained rises that were assumed in the scenario.
Over the past decade, global emissions have more closely tracked RCP4.5, one of the two “medium stabilisation scenarios” of the original four RCPs.
The debate around RCP8.5 has not just focused on current emissions, but also on the scenarios underlying assumptions for the future.
When it was published in 2011, the world had just seen unprecedented growth in global CO2 emissions, which had increased by 30% over the previous decade. Global coal use had increased by nearly 50% over the same period. Cleaner alternatives remained expensive in most countries and the idea of continued rapid growth in coal use seemed realistic.
Critics of RCP8.5 point to its assumptions for a dramatic expansion of coal use in the future, as well as high growth in global population.
For example, in a 2017 paper, two scientists argued that the “return to coal” envisaged in RCP8.5 would require an unprecedented five-fold increase in global coal use by the end of the century. Such an outcome was “exceptionally unlikely”, the authors wrote.
However, others have argued that while high-emissions scenarios are becoming increasingly unlikely, they still have an important role to play. For example, they highlight risks that only emerge under higher levels of warming.
In addition, research has shown that feedbacks in the climate system – where warming triggers the release of more CO2 and methane, which warms the planet further – could mean that human-caused emissions lead to a higher radiative forcing and have a greater climate impact than initially assumed.
How has RCP8.5 been replaced?
As the IPCC heads into its seventh assessment cycle (AR7), scientists have been developing the emissions scenarios and climate model projections that will – eventually – feed into its reports.
For the emissions scenarios, that process – known as ScenarioMIP – started back in 2023 at a meeting in Reading, UK. This involved scientists representing “different climate research communities”, explains van Vuuren.
This “brainstorming” session devised the outlines for the new scenarios, he says. After more meetings, these were subsequently developed into a proposal that was – after review – translated into a journal paper. After review from scientists and the public, the final paper was published in April.
The paper sets out seven all-new emissions scenarios, replacing the SSPs (and its predecessors, the RCPs). For simplicity, the new scenarios are named according to their levels of greenhouse gas emissions.
The figures below show the emissions (left) and the estimated global temperature changes (right) under the proposed scenarios, from the “low-to-negative” emissions scenario (turquoise) up to a “high-emissions” scenario (brown).
(It should be noted that, while the ScenarioMIP paper has been published, there remains an embargo on using the scenario data produced by integrated assessment models – often referred to as IAMs – to publish academic papers, analysis or even social media posts until 1 September this year. Carbon Brief will publish a detailed explainer on the new scenarios once the embargo lifts.)
When compared to the SSPs that came before, the range in future emissions in the new scenarios “will be smaller”, the authors say in the paper:
“On the high-end of the range, the…high emission levels (quantified by SSP5-8.5) have become implausible, based on trends in the costs of renewables, the emergence of climate policy and recent emission trends…At the low end, many…emission trajectories have become inconsistent with observed trends during the 2020-30 period.”
In other words, the combination of technological progress and action on climate change that, to date, remains insufficient, means that scenarios of very high or very low emissions are now not considered plausible.
Another way of looking at it is that the “range of potential futures has narrowed”, explains Smith, one of the authors on the paper.
If you “draw a fan or plume of potential future emissions that start in 2025”, it lies entirely within the spread of scenarios from a decade ago, he says:
“So you’ve ruled out futures at the high end. You’ve also ruled out futures at the low end – so it’s now not possible to limit warming to 1.5C, at least in the short term or the medium term.
This is a mix of “good” and “bad” news, Smith adds.
“In the latest set of scenarios, the lowest [scenario sees] peaking at about 1.7C, so we’ve also lost that low end, but the good news is we’ve lost the high end…Back in 2010, RCP8.5 wasn’t an implausible future, we’ve now made it an implausible future, because we’ve actually bent the curve [on emissions] enough to eliminate that possibility.”
The new “high” scenario projects warming in 2100 of closer to 3.2C (with a range of 2.5C to 4.3C).
To be clear, this “high” scenario would still come with catastrophic climate impacts, even if the level of warming would remain slightly below what was set out in RCP8.5.
Van Vuuren adds that the world is “now on a trajectory to 2.5-3C of warming”. As a result, “we don’t have any scenario anymore that can reach 1.5C with limited overshoot – we will have a significant overshoot”.
How is the IPCC involved?
Contrary to Trump’s claims, the common set of future emissions scenarios used by climate scientists are not developed by the IPCC, the UN climate-science body that produces landmark reports about climate change.
Instead, the development process described above is driven by a group of Earth system modelling experts convened by the Coupled Model Intercomparison Project (CMIP).
CMIP – an initiative of another UN body, the World Climate Research Programme – coordinates the work of dozens of climate modelling centres around the world.
Working in six-to-eight year cycles, CMIP asks modelling centres around the world to run a common set of climate-model experiments – simulations that use the same inputs and conditions – that allows for results to be collected together and more easily compared.
For experiments that explore how the climate might change in the future, modelling centres are instructed to run simulations against a fixed set of future climate scenarios, each with different levels of concentrations of greenhouse gases, aerosols and other drivers of climate change.
These future emissions scenarios are revisited each time CMIP embarks on a new “phase” of climate-modelling coordination, to reflect advances in scientific understanding and the pace of real-world climate action.
The group tasked with producing the design of future scenarios, as well as the “input files” for climate models, is the “scenario model intercomparison project”, or ScenarioMIP.
CMIP aligns its work with the schedule of the IPCC, coordinating a new set of model runs for each IPCC assessment cycle.
For example, the IPCC’s AR5 in 2013 featured climate models from the fifth phase of CMIP (CMIP5), whereas AR6 in 2021 used climate models from CMIP’s sixth phase (CMIP6).
AR7 will feature models from CMIP’s ongoing seventh phase (CMIP7). The first results from CMIP7 model runs are expected later this year.
The IPCC is consulted during the CMIP process, van Vuuren tells Carbon Brief, but their input is “no different from any other review comment” that the ScenarioMIP team received.
Thus, while the IPCC relies on model runs coordinated by CMIP in its landmark reports, it does not play a role in designing future emissions scenarios, nor in deciding when they should be retired.
Dr Robert Vautard, co-chair of IPCC AR7 Working Group I, tells Carbon Brief that the IPCC does not “do or coordinate research”. Its role, he says, is to “synthesise existing knowledge” and produce “regular” reviews of climate-science literature.
He adds that ScenarioMIP is just one set of scenarios the climate-science body assesses in its reports:
“IPCC assesses all scenarios, or sets of scenarios, that the scientific community produces. IPCC does not produce scenarios. CMIP7 will be [one] set of scenarios assessed by IPCC [for AR7] – but there will be many others.”
The post Factcheck: Trump’s false claims about the IPCC and ‘RCP8.5’ climate scenario appeared first on Carbon Brief.
Factcheck: Trump’s false claims about the IPCC and ‘RCP8.5’ climate scenario
Climate Change
Corpus Christi Leaders Believe Data Center Plans May Be Behind Delays to Emergency Water Supply
Authorities in Sinton won’t confirm or deny Corpus Christi’s suggestion that the small town is hoarding its precious groundwater for data centers. Across Texas, a booming buildout of server farms is adding strain to water resources that are already stretched to their limit.
This story was produced in partnership by Inside Climate News and the Texas Newsroom, the state’s network of public radio stations.
Corpus Christi Leaders Believe Data Center Plans May Be Behind Delays to Emergency Water Supply
Climate Change
New Zealand Moves to Ban Tort Liability for Greenhouse Gas Emissions and Climate Damage
The move comes as the American Petroleum Institute and Republicans in Congress push legislation in the U.S. to shield the oil and gas industry from climate accountability.
New Zealand’s government has announced that it plans to amend the country’s signature climate law to prohibit liability arising from climate change damages, a controversial move that critics say would shield polluters from climate lawsuits and undermine the rule of law. It comes amidst recent legislative action from Republican lawmakers in the U.S. to similarly restrict liability for climate-related harms.
New Zealand Moves to Ban Tort Liability for Greenhouse Gas Emissions and Climate Damage
How Climate Change Is Raising the Cost of Living
Factcheck: Trump’s false claims about the IPCC and ‘RCP8.5’ climate scenario
Corpus Christi Leaders Believe Data Center Plans May Be Behind Delays to Emergency Water Supply
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