Climate Tipping Points Fact-Check series: Introduction

In the last year there has been a surge in interest in and news on climate change, inspired in part by high-impact reports like the IPCC’s special report on keeping global warming within 1.5°C (which gave a limit of only 12 years for significant emission cuts) and the Hothouse Earth paper, along with an intense summer wildfire season and the fifth year of record-breaking temperatures. This has been accompanied by a wave of new climate activism seeking to initiate greater action on achieving decarbonisation to limit climate change, such as the School Strike for Climate movement started by Greta Thunberg in Sweden. 2018 also saw the start of the Extinction Rebellion (XR) movement in the UK, who have organised non-violent civil disobedience inspired by their popular Heading for Extinction speaking tour in dozens of towns in the UK.

But some activists, journalists, and academics have recently made widely seen and circulated claims that several climate tipping points may have already been triggered and that devastating warming is now almost inevitable. Commonly discussed scenarios include:

  • An ice-free Arctic will happen within the next few years and trigger a “Blue Ocean Event”, leading to a sudden and devastating increase in global warming
  • A “Methane Bomb” scenario, in which vast amounts of the potent greenhouse gas methane is released soon from the Arctic, triggering sudden catastrophic warming
  • That even if we stopped emitting greenhouse gases now, we’re already committed to catastrophic warming far worse than the 1.5°C or 2°C Paris targets
  • That “Global Dimming” from aerosol pollution is masking a large amount of warming, so a cut in emissions would actually trigger sudden dangerous warming
  • That there are no significant stabilising negative feedbacks that counter the self-reinforcing positive feedbacks in the climate system, leading to runaway warming
  • The events of the Permian-Triassic Extinction 252 million years ago – in which 90-95% of all species died out in the “Great Dying” – could soon happen again

Many of these scenarios rely on the premise that many climate tipping points are on the verge of being triggered, and these will cause immediate and severe climate consequences rather than acting as gradual irreversible feedbacks.

Extreme climate scenarios have been posited before by fringe activists and commentators, but they are now entering into more mainstream activist, political, and media discussion. There has also been growing awareness and interest in the scientific (and not-so-scientific) discussion of climate tipping points and feedbacks, and has led to a surge in hits for by people wanting to find out more.

While this increase in interest in climate tipping points and their implications is welcome, some scientists are worried that the attention-grabbing extremely unlikely catastrophic scenarios are dominating discussions. Many articles take the worst-case scenario (or beyond) and assume it is likely or even certain, when in reality they have a low – but importantly not insignificant – chance. And although climate change in some cases (like sea level or sea ice loss) is happening faster than the IPCC originally projected, and many models do not yet fully include the tipping points and feedbacks we know of, this doesn’t mean that the IPCC is unreliable and that the worst-case scenario is now inevitable.

On the other hand, there are also many commentators and politicians who are still sceptical that serious climate change exists at all. In trying to be clear about the realities and uncertainties of climate tipping points we should not give false comfort and suggest that they are not a problem. Climate change is a matter of uncertain risks, with tipping points making higher warming scenarios more likely and ‘lukewarm’ scenarios less likely.

For example, some recent analyses have found that on current emission trajectories we have a 50% chance of exceeding 3.2°C and a 5% chance of exceeding 4.9°C by 2100 (and conversely only a 5% chance of keeping below the 2°C Paris target). However, adding some possible climate tipping points and feedbacks moves the 50% value up to 4.1°C and the upper 5% value up to 6.5°C, values well into the realms of what many believe represents an existential risk. A 5% chance seems low, but it represents a one-in-twenty chance of an unacceptable outcome. Discussions of the extreme possibilities should be clear that they are still unlikely, but still likely enough to make these scenarios well worth avoiding by keeping below 1.5-2°C as a safe precaution. Climate tipping points load the dice a bit more against us, but are not yet a foregone conclusion.

In this new Fact-Check series, aims to clear up some confusion about climate tipping points, so that people can be clear about how best to act as a result. The conversation about climate tipping points is important and needs to be well informed in both what we know and what we don’t know, otherwise we risk the discussion becoming mired with misinformation and its warnings unheard.

Click each link below to find out more about each claim and the reality behind it (links will be updated as the series is published):

Fact-Check: will an ice-free Arctic trigger a climate catastrophe?

Claim: A summer ice-free Arctic (called by some the “Blue Ocean Event”) will happen within the next few years and will cause an abrupt worsening of climate change and possible runaway feedbacks.

Reality: A summer ice-free Arctic will probably happen within the next few decades, but the exact year will depend on unpredictable natural variability. A summer ice-free Arctic would worsen regional warming and impacts, but would not cause a big or sudden increase in global temperatures.

Fact-Check: do tipping points and feedbacks commit us to rapid catastrophic warming?

Claim: More than 3°C of warming is already locked in over the next ~10 years even if we reduced or stopped emissions now, making catastrophic warming inevitable.

Reality: By 2030 we’ll likely reach an average of ~1.3oC. If all carbon emissions ceased now we’d reach ~1.7°C by 2100 (and more with reduced aerosol emissions), but our current trajectory is for far higher. Many of the values in committed warming lists are excessive, double-counted, or happen far slower than claimed.

Fact-Check: is an Arctic “Methane Bomb” about to go off?

Claim: A huge amount of methane is trapped in permafrost and methane hydrates in the Arctic and is starting to leak out, and even a partial release could at any time trigger a sudden shock increase in global warming of up to 5°C within 5 years.

Reality: Methane levels have recently increased but so far have a mainly tropical or fossil fuel source. Methane release from permafrost and hydrates will happen as a gradual chronic leak acting as an unwelcome but modest feedback on warming, rather than being a sudden, catastrophic release.

Fact-Check: is “global dimming” shielding us from catastrophe?

Claim: Global dimming (due to cooling by aerosols, as opposed to global warming from greenhouse gases) is masking a large amount of warming (0.7-1.5°C), so if we stopped carbon emissions now we’d get a catastrophic jump in global warming.

Reality: Global dimming is masking around 0.6°C of anthropogenic warming. There are many aerosol sources – including some that cause warming – and so shutting down the worst carbon emitters (like coal power stations) now would not lead to all aerosols disappearing immediately or a sudden, dramatic warming.

Fact-Check: will 2°C of global warming trigger rapid runaway feedbacks?

Claim: Once global warming reaches 2°C (which we’ve nearly reached already, but scientists are downplaying it), positive feedback loops and tipping points will trigger rapid runaway warming and guarantee apocalyptic climate change in the next few decades.

Reality: The risk of tipping points grows significantly above 2°C, but this is an uncertain precautionary boundary and not a sharp definite threshold. Most feedbacks are long-term, committing to a Hothouse by the year ~3000 rather than 2100. Current warming is 1.1°C above the 1850-1900 baseline, not ~2°C. The 1.5°C & 2°C targets are still geophysically possible, and reduce the risk of passing more tipping points.

Fact-Check: are there no negative feedbacks to stop runaway warming?

Claim: There are lots of amplifying positive feedbacks in the climate system and no significant stabilising negative feedbacks, making runaway climate change likely.

Reality: Outgoing longwave radiation acts as the main major negative feedback, as hot things radiate more heat away. Positive feedbacks do not inevitably lead to runaway warming, as negative feedbacks will eventually counter them – if there were no negative feedbacks Earth would have become as hot as Venus long ago.

Fact-Check: are we re-triggering the Permian-Triassic Extinction?

Claim: Four out of five previous mass extinction events were caused by massive CO2 increases triggering methane releases, stagnant oceans, and crashing oxygen levels and led to 95% of life dying, and human warming is on the verge of doing the same.

Reality: Only two past extinctions definitely featured CO2-driven warming (PTX & TJX), with another two featuring CO2-linked cooling. The Permian-Triassic extinction featured far more extreme emissions and was amplified by many other factors that are not the case now. A total plankton die-off and low oxygen is nigh-on impossible.

Fact-Check: are climate tipping points always sudden and dramatic?

Claim: Tipping points are always abrupt events with big, immediate impacts. Passing a climate tipping point like with Arctic sea-ice or methane release will result sudden jumps in warming within only a few years.

Reality: The most important feature of tipping points is irreversibility, even if they only happen gradually. Once a process passes a tipping point it will keep on going even if you remove the initial driver. For example, Arctic methane may start leaking out even if we cut back emissions, but it’ll come out over centuries rather than years.


This post was written by Dr. David A. McKay, currently a Postdoctoral Researcher at Stockholm Resilience Centre (Stockholm University), where he is part of the Earth Resilience in the Anthropocene Project (funded by the European Research Council) and is researching non-linear climate-biosphere feedbacks. This post was written in his spare time with no funding support for this site, and was proofread and edited by Dr. Rachael Avery.


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