Do Tipping Points mean Runaway Global Warming after 12 years?

Is it 12 years?

That’s a belief I am finding increasingly common, but it really isn’t what the science is telling us.

The science is saying that things are very serious and every year we fail to “bend the curve down” as Greta Thunberg puts it, the worse the outcomes. We know from the IPCC (Intergovernmental Panel on Climate Change) 1.5oC Special Report that 2oC is significantly, perhaps surprisingly, worse than 1.5oC.

That is not a reason for a dystopian view that all is lost if we fail to get to zero after 12 (or is it now 11 years) if we don’t get to net zero by then.

The science is not that certain. The IPCC said that 2030 global net emissions must reduce by 45% versus 2010 emissions to achieve 1.5oC, and get to zero by 2050.

That is not to say we should not have highly ambitious targets, because the sooner we peak the atmospheric concentration of CO2 in the atmosphere, the sooner we peak the global warming (see Note 1).

Because it is such a huge challenge to decarbonise every sector of our economies, we should have started 30 years ago, and now we have to move very fast; whatever date you put on it. So, if I question some of the dystopian memes out there it is certainly not to question the need for urgent action.

Feedbacks and Tipping Points

I think what lies at the root of the dystopian message is a belief that tipping points – and there are quite a number in the Earth system – are like dominoes, and if one goes over, then all the rest follow. At a meeting I went to that included policy experts, XR, scientists, and others, I got into a chat about feedbacks and tipping points.

The person I spoke to was basically 100% convinced that if we did not get to net zero after ’12 years’ we would set off feedbacks and tipping points. It really would be game over. I want to summarise my side of the conversation:

I appreciate your concern about tipping points; they are real and need to be taken into account.

It is complicated and there are cases that can runaway (take Venus), but there is often a response that limits a particular feedback.

For example, extra CO2 causes warming, which due to the Clausius–Clapeyron relation means that additional water vapour (gaseous form of water, not clouds) is added to the atmosphere (7% extra for every 1C of warming). Since H2O is also a strong greenhouse gas that causes more warming.

This is a crucial ‘fast feedback’ included in climate models. It means that the expected 3oC of warming from doubling CO2 in the atmosphere is actually 1oC from the CO2 and 2oC extra from the H2O feedback (see Note 2).

Ok, so why doesn’t this warming carry on as a runaway (there is plenty of water in the ocean)?

The reason is Stefan’s Law (or ‘Planck Response’).

A body at temperature T emits energy at a rate proportional to T to the power 4. So the loss of heat accelerates and this at some points stops the feedback process (see Note 3).

A way to think about this is a plastic container with a hole at the bottom (say 7mm wide). Pour water from a tap at a constant rate, say half a litre per minute, into the container. What happens? The water level in the container rises to a point that maintains this level. At this point the pressure at the base of the container has increased to the point that the rate of flow of water out of the bottom is equal to the rate of flow in. They are in balance, or ‘equilibrium’.

If I now plug the 7mm hole and drill a 6mm one instead (yes I did this for a talk!), then with the same flow rate coming in, the level of water rises, because it requires more pressure at the base to drive water out at the rate required, to bring the system back into balance (when the level of water stops rising).

We are in both cases having the same amount of energy leaving as entering the system, but in the latter case, energy has been trapped in the system. 

This is a very good analogy for what happens with the Greenhouse Effect (see Note 4), and the level of water is analogous to the trapped energy (which means a hotter planet), and the world warms even though the rate at which energy is coming in (from the Sun) is constant. We can explain the Greenhouse Effect via this analogy simply:

The increased heat trapping power of the atmosphere with an increased concentration of COrestricts the exiting (infra-red) radiation to space – this is analogous to the reduced hole size in the container – and so …

The temperature of the Earth rises in order to force out radiation at the correct rate to balance the incoming energy – this is analogous to the increased level of water in the container. 

This demonstrates that the planet must stabilise the flow of energy out so that it equals the energy in, but with extra energy behind captured in the process (see Note 5).

The main point is that feedbacks do not inevitably mean there is a runaway.

Professor Pierrehumbert wrote a paper reviewing the possibility of a runaway in the sense of heading for a Venus scenario, and it seems unlikely “it is estimated that triggering a runaway under modern conditions would require CO2 in excess of 30,000 ppm”.

Even in more complex cases, such as melting sea ice and ice sheets, the feedbacks do not imply inevitable runaway, because in each case there is often a compensating effect that means a new equilibrium is reached.

But there is not one possible end state for a particular level of warming, there are numerous ones, and we know from the climate record that flips from one state to another can happen quite fast (the ocean conveyor belt transports huge amounts of heat around the planet and this is often implicated in these rapid transitions).

So, this is not to say that the new equilibirum reached is a good place to end up. Far from it. I agree it is serious, and the level of CO2 in the atmosphere is now unprecedented for over 3 million years. We are warming at an unprecedented rate, thousands of times faster than the Earth has seen in that period.

It is very scary and we don’t need to say a runaway is inevitable to make it even more scary!

Arguments that a feedback will trigger another, and so on, ad infinitum, may sound plausible but are not science, however confident and high profile the speaker may be. It does the XR cause no good to simply repeat wild speculation that has no scientific foundation, merely on the basis of a freewheeling use of the ‘precautionary principle’.

I hope this clarifies my point, which was not to minimise the urgency for action – far from it – I am 100% behind urgent action.

However, I think that sometimes it is important to be scientifically pedantic on the question of feedbacks and runaway. The situation is scary enough.

I really worry about the dystopian message for our collective mental health, and that this might freeze people and even limit action amongst the wider public who are not activitists (but need to participate in our collective actions).

We need a message of hope, and this is it:

The sooner we can peak the atmospheric concentration of CO2 (by stopping emissions), the sooner we can halt warming, and

the lower that peak in the atmospheric concentration, the lower the level of warming.

We can make a difference!

We have to act to make hope meaningful, because being alarmed, and frozen in the headlights, and unable to act, is not a recipe for hope.

However, being duly alarmed and having hope are not mutually exclusive, if we recognise we have agency. We can all make a contribution, to agitate for, or implement, a plan of actions and the actions that follow.

(c) Richard W. Erskine, 2019



(1)   The IPCC 1.5C Special Report (p.64) talks about ‘committed warming’ in the oceans that is often assumed to mean that the Earth will continue to warm even when we stop CO2 emissions due to thermal inertia of heated oceans. Surprisingly for many, this is not the case. The IPCC reiterate what is a long known effect, regarding what they term the Zero Emissions Commitment:

“The ZEC from past COemissions is small because the continued warming effect from ocean thermal inertia is approximately balanced by declining radiative forcing due to COuptake by the ocean … Thus, although present-day CO2-induced warming is irreversible on millennial time scales … past COemissions do not commit substantial further warming”

(2)   This excludes clouds, and the effect of clouds at lower and higher levels can, for this simple example, can be regarded as cancelling each other out in terms of warming and cooling. Water Vapour in the atmosphere referred to here is not condensed into droplets but is a gas that is transparent to the human eye, but like carbon dioxide, is a strong absorber of infra-red. Because carbon dioxide is a non-condensing gas, but water does condense, it is the concentration of carbon dioxide that is the ‘control knob’ when it comes to their combined warming effect.  In 1905, T.C. Chamberlin writing to Charles Abbott, eloquently explains the feedback role of water vapour, and the controlling power of carbon dioxide:

“Water vapour, confessedly the greatest thermal absorbent in the atmosphere, is dependent on temperature for its amount, and if another agent, as CO2 not so dependent, raises the temperature of the surface, it calls into function a certain amount of water vapour, which further absorbs heat, raises the temperature and calls forth more [water] vapour …”

(3)  Strictly, it is a ‘black body’ – that absorbs (and emits) energy at all frequencies – that obeys Stefan’s Law. When using the law, we express T in Kelvin units. To a reasonable approximation, we can treat the Earth as a black body for a back of the envelope calculation, and we find that without carbon dioxide in the atmosphere, the Earth – at its distance from the sun – would be 258K, or -15oC on average, a frozen world. That would be 30oC colder than our current, or pre-industrial, average of 15oC.

(4) John Tyndall originated this analogy in his memoirs Contributions to Molecular Physics in the Domain of Radiant Heat published in 1872, although he used the example of a stream and dam, which is raised, my exposition is essentially based on his precedent.

(5) One other aspect of this re-established equilibrium is that the so-called ‘Top of Atmosphere’ (TOA) – where the energy out in the form of infra-red, is balancing the energy in – is at higher altitiude. The more carbon dioxide we add, the higher this TOA. Professor Pierrehumbert explains it in this Youtube exposition, from the film Thin Ice, where he pulls in a few other aspects of the warming process, as it works on planet Earth (e.g. convection).



Filed under Climate Science, Science Communications

7 responses to “Do Tipping Points mean Runaway Global Warming after 12 years?

  1. AA

    Thank you for writing this. What about the case where melting Arctic sea ice heats the Arctic Ocean, thawing the permafrost under the seabed of the East Siberian Arctic Shelf (very shallow c.50m deep sea), and thereby releasing methane from the gigatons of methane hydrate deposits that can bubble up through the shallow sea and escape into the atmosphere? Even a tiny fraction of the methane escaping would equate to tens of gigatons of methane. What would be the stabilising factor in this scenario? (that would prevent runaway warming)


    • Thanks for the comment. In the case of sea ice, the balancing ‘force’ is, simply, winter. See … however, the prospect of sea-ice free summers is increasingly likely within a matter of decades. There is also the concern that while there is winter re-icing, we are losing a lot of ‘old ice’, and it also depends on how the heat in the warming oceans is distributed. It is certainly a bad situation for artic sea-ice, but it is not as simple as saying there is an inevitable feedback to zero ice. It will depend on how much more carbon dioxide we emit (I need to pop out now so will come back to you on the other points). I recommend you follow @kevpluck on Twitter who does some brilliant animations related to the cryosphere.


    • AA, my response to Gravandrew includes a response on methane escape, so I won’t repeat that here (I was thinking of both of you when responding). The stabilising factors are the degradation of methane, which will be effective if the release is ‘not too fast’. The Planck Response always applies, not preventing warming, but acting like a ‘governor’ to enable a new equilibrium to be reached, albeit in many cases not one we wish to end up in, but not a dominoe effect at least (was my original point).


  2. gravandrew

    Thanks for the link & Twitter suggestion. If we could focus this example on, say, the energy absorption by the ocean during summer of the East Siberian Arctic Shelf (due to massive loss of summer sea-ice extent, that’s already taking place), with that energy warming the shallow ESAS water and thawing the permafrost under the seabed, leading to release of methane from the methane hydrates – that’s the specific scenario I’m interested in knowing whether the Earth can find an equilibrium from, say, a 50Gt methane release, or whether that would be the start of more warming and thawing of permafrost. I ask, because of recent direct observations from the Academic Mstislav Keldysh research ship of methane bubbling out of the sea, and current daily measurements of methane over the Arctic by the Copernicus Sentinel 5P satellite. I’m aware some experts have dismissed the possibility of an abrupt, massive release of methane from the ESAS, and I’m equally aware of other experts who haven’t – so I’m very interested in, given an hypothetical abrupt 50Gt+ methane release, how Earth’s system would find an equilibrium that prevents runaway warming. I am very much hoping there is one, which is why your blog post was of such interest to me. Perhaps we’d just have to rely on ‘Stefan’s Law’ in such a scenario, accepting whatever consequences there’d be in a sudden addition to global temperatures.


    • This is a contested area. Some basics first. While a molecule of methane is say 25 times more ‘heat trapping’ than a moelecule of carbon dioxide, an increased concentration of methane in the atmosphere is not ‘long-lived’- a matter of years – whereas for carbon dioxide it is (methane is broken down through atmospheric chemistry into carbon dioxide no less). So comparing their ‘global warming potential’ is not so trivial (the film Cowspiracy made this error, which undermined the film, even though livestock methane IS an issue). Currently, carbon dioxide remains the biggest greenhouse gas issue. The issue with warming tundra is therefore very worrying but very much depends on the rate at which it is released. If it is a slow enough rate, the degradation of the methane could significantly offset the release of the gas (this is the counteracting effect, if you like, in addition to the Planck Response [Stefan’s Law], of course that applies across the board). You talk of hypothetical 50Gt+ methane release, but I think the discussion needs to look at realistics scenarios. Prof. David Archer is quite critical of the talk of methane hydrates (a methane bomb some call it) as a realistic scenario because they are not lying is easy reach of the ocean floor, and any proposed mechanism has to deal with actual geological/ chemical realities (see article here I still believe that the key focus is on getting to zero carbon dioxide emissions, because if we do that, we can take a whole lot of feedbacks effectively out of play. The danger from a communications perspective is we spend too much time discussing future debatable scenarios, when we have the reality of our current climate emergency. The deniers like to talk of future energy such as Fusion, and I call this ‘techno-fetishist delayism’, but those like myself who are alarmed (not in denial), can equally spend too much time in a dystopian future, instead of working on the transition that is needed today and tomorrow. That is my take.


  3. gravandrew

    Thanks Richard for this detailed answer, it provides info I can use in follow up research on this issue (btw: ‘gravandrew’ and ‘AA’ are two posts by me, thanks for answering both). I understand CH4’s residence time in the atmosphere is, on average, only about 8-9 years, but it’s GWP, using UNFCCC data, is 56 over 20yrs, 21 over 100yrs, and 6.5 over 500yrs ( – which I assume is the best data we have for it at the moment ( gives similar figures) – and that’s not insignificant (and already takes into account the various methane oxidation pathways that break it down). I haven’t seen Cowspiracy, but it looks like (from a quick search) they got their data wrong (e.g. overstating the % of GHG directly contributed by animal farming).

    I agree CO2 is currently the biggest GHG issue, because IPCC hasn’t accounted for unanticipated release of GHGs from permafrost or methane hydrates in their assessments (stating such in TFE.8 WG1AR5). To my mind, it’s like a wildcard factor, and I appreciate it’s a contested issue. I agree that much depends on the rate of release, and it’s the probability of an abrupt, massive release that’s highly contested.

    With regard to what’s a ‘realistic scenario’, thanks for mentioning Prof. David Archer, I’ll look more deeply into his work, plus the MotherJones article you link to. I notice the MotherJones article is from August 2013, when this was being debated. In terms of “actual geological/ chemical realities”, I refer you to the recent June 2019 paper “Understanding the Permafrost–Hydrate System and Associated Methane Releases in the East Siberian Arctic Shelf” by Shakhova, Semiletov and Evgeny Chuvilin (, which I appreciate you might already be familiar with. I hope you’ll agree they are world experts when it comes to methane hydrate deposits of the ESAS, and they state “The lack of understanding of this process creates some of the largest uncertainties in climate research related to cryosphere–climate–carbon couplings”. They point out how much is unknown, and call for an extensive monitoring network to be set up to better understand the likelihood of sudden, large-scale CH4releases.

    So, whilst I agree with you that resources to tackle the climate emergency are limited, and getting to net Zero CO2 emissions is critical (and will reduce other dangers), I’m not sure that the ‘ESAS methane release’ potential is a “future debatable scenario”, because of its unique potential to make our CO2 emissions irrelevant. The Arctic is warming at an astounding rate. Your mentioning of the Planck Response as something that helps the Earth system tend towards equilibrium is reassuring to some extent, and it’s something I’ll look into far more deeply than I have done so far.


  4. Will Mayall

    It would seem that the big issue with “tipping points” is that they are so very complex and we almost certainly know so little. There also seems to be little knowledge regarding how the various systems behind tipping points may interact to create even more complex tipping points. For example, do ocean currents, polar ice, and permafrost melting interact?

    Given that we know so little, is it any wonder that many of us err on the side of doom and gloom?


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