This is scaring some people - because they describe dramatic things that could happen like floods tens of meters deep, and the world too hot for humans. Most of this is for far into the future. The sea rising 10s of meters would be thousands of years into the future - many of the news stories didn’t make that clear.


The article is mainly about things that could happen centuries to thousands of years into the future. It doesn't really conflict with the IPCC who have already concluded that these tipping points may have significant but probably minor effects before 2100 - because it is a meta study and it is just looking at ideas for future research. There are no dates in it, and there is no new fundamental research.

They are saying there are things we can do in the next couple of decades that can get the Earth into a good state, one in which it will neither get too hot nor too cold for hundreds of thousands of years.

They call this “Earth System Stewardship”

They talk about three scenarios, the Hothouse Earth, "Stabilized Earth" and "Glacial Interglacial cycle". We have already moved out of the last of those - we have probably done enough already to avert any future ice ages. So that's actually good. So the remaining options are the "stabilized Earth" where for hundreds of thousands of years Earthjust stays stable, and "Hothouse Earth" where it goes looping around to some very hot state and then back to where it is now.

They say that we should aim for the "Stabilized Earth" and they think that these tipping points mean that if we don't take the opportunity right now it will be much harder for people later on to make that choice. I.e. that there are things we can do in the next decade or two that will make life much easier for our grandchildren and great grandchildren.

It is an idea however and not proved, it is a suggestion for other researchers to follow up to see if what they suggest is right.

They say that we shoud work on not just being carbon neutral but carbon negative, to have forests and also machines for removing CO2 from the air.

Other scientists are skeptical of this report. It is not proved and there are no actual future dates in the article. It is all qualitative about things that might happen, mostly centuries to millenia into the future..


They recommend that we keep well within 2 C This is still possible.

The Paris agreement pledges are for 3.6 °C so far, but with the aim to ramp up to 1.5 °C.

It depends a lot on China if we can get within 1.5 °C, because this needs action quickly and China have said they will increase the proportion of green energy but will also increase the total power capacity through to 2030, they have said they will reach maximum emissions before 2030 but don’t say when. But they are making good progress and despite a glitch of an increase in power from coal last year, it might be that 2018 is their maximum emissions year. If so, then 1.5 °C seems a goal within reach.

We'd also need the US on board - but much of the US is already doing their best even while Trump is aiming to withdraw from Paris. Other countries are already ramping up their targets with several aiming to be carbon neutral by 2030 and earlier. Mainly small countries but - it's definitely possible.


The main message of this paper is that the authors think that once we reach 2 °C above pre-industrial then there may start to be some feedback effects that will put us on a path towards eventually getting much hotter (though they don’t say how hot, or over what timesecale).

So they are arguing to stay well within 2 °C. Although most events won’t play out for a long period of time, they say we need to act quickly because once we go over this level then various things start happening that, even thought hey may happen slowly, are hard to reverse. Such as the start of a long slow release of the carbon stores in the Siberian permafrost. They think that to avoid this happening, we should not just go carbon neutral, and stay within 2 °C by 2100, but aim to go carbon negative - to start taking carbon out of the atmosphere, as trees and through carbon capture and storage.


The press release didn’t give timescales, and many of the news stories just riffed off the press release, and the authors don’t read the paper itself. When you read the paper, they still don’t give timescales, but it becomes clear that for most of this, they are talking about things that could happen over centuries to millennia.

They are not conflicting with the IPCC, which does climate projections mainly through to 2100. It is more that they are looking at a much longer future timescale.

Also, they don’t have any proof, and no new data or research. As they say in their conclusion:

Our initial analysis here needs to be underpinned by more in-depth, quantitative Earth System analysis and modeling studies to address three critical questions. (i) Is humanity at risk for pushing the system across a planetary threshold and irreversibly down a Hothouse Earth pathway? (ii) What other pathways might be possible in the complex stability landscape of the Earth System, and what risks might they entail? (iii) What planetary stewardship strategies are required to maintain the Earth System in a manageable Stabilized Earth state?

It is all qualitative. The diagrams in it are just sketches with an arrow indicating time - but no markers along the time axis of centuries or millennia. It isn’t really adding anything new over the previous studies. It is more of a meta study.a result of looking at many other papers and then drawing up a hypothesis for other scientists to study


This is one of their diagrams:

There they say that we would notmally be heading towards an ice age in the blue loop. But instead we seem to be loopiong around in the smaller “Stabilized Earth” which is actually a rather good scenario to end up in.

If we stay well within 2 C, which is the ideal target of the Paris agreement, to stay within 1.5 C, then we are good for hundreds of thousands of years into the future, to have a stable temperature without the huge fluctuations of the ice ages.

However they say we are at a kind of decision point where the things we do for the next several decades could tip us into the “Hothouse Earth” cycle. That then could lead to Earth getting a lot hotter centuries to more like thousands of years into the future.


The article may seem to conflict with the IPCC which says we reach only 3.6 °C above pre-industrial by 2100. However, that’s not its real focus. It does not attempt to predict any temperature for 2100.

Now they don’t mean that we can transition to the Hothouse Earth right away.

“Hothouse Earth is likely to be uncontrollable and dangerous to many, particularly if we transition into it in only a century or two, and it poses severe risks for health, economies, political stability (12, 39, 49, 50) (especially for the most climate vulnerable), and ultimately, the habitability of the planet for humans.”

So - they are saying that we have to be careful about not getting into the loop that leads to a hotter Earth within the next one or two centuries.


The IPCC who do the climate change projections acknowledge that there are some things they leave out of their projections. They give reasoning about why they think it is okay to leave them out. See IPCC review of research from 2017

Permafrost: …. This led to a new estimate that about 100 Pg of cumulative carbon emissions (with a wide uncertainty) would be released from thawing permafrost by 2100 under RCP8.5. This leads to a significant positive feedback, but the review emphasised that emissions are “likely to be gradual and sustained rather than abrupt and massive”. A recent modelling study estimated that permafrost carbon releases could contribute up to 12% of the change in global mean temperature by 2100 Studies since 2013 therefore confirm the importance of permafrost carbon release as a positive feedback, and the need to include it accurately in Earth system models, but they do not support considering it to exhibit threshold behaviour.

Clathrates: Some economic assessments continue to emphasise the potential damage from very strong and rapid methane hydrate release, although AR5 did not consider this likely. Recent measurements of methane fluxes from the Siberian Shelf Seas are much lower than those inferred previously. A range of other studies have suggested a much smaller influence of clathrate release on the Arctic atmosphere than had been suggested. …. A recent modelling study joined earlier papers in assigning a relatively limited role to dissociation of methane hydrates as a climate feedback. Methane concentrations are rising globally, raising interesting questions (see section on methane) about what the cause is, finally new measurements of the 14C content of methane across the warming out of the last glacial period show that the release of old carbon reservoirs (including methane hydrates) played only a small role in the methane concentration increase that occurred then.

Amazon rainforest: The processes acting on tropical rainforests are very complex and a recent review still emphasised the possibility of a climate threshold … Recent work using a detailed ecosystem model (Levine et al., 2016) supports the possibility of a significant but heterogeneous transition in biomass type dependent on the length of the dry season, but in a continuous rather than “tipping point” manner. Resilience may be underestimated if plant trait diversity is not included in models


So, anyway, in this paper, they are saying that they think, without actually calculating anything - that these feedback effects, although not necessarily individually significant, might have a domino effect where each one affects the others and so that overall the effect is significant - at least on the very long term.

“We suggest 2 °C because of the risk that a 2 °C warming could activate important tipping elements (12, 17), raising the temperature further to activate other tipping elements in a domino-like cascade that could take the Earth System to even higher temperatures (Tipping Cascades). Such cascades comprise, in essence, the dynamical process that leads to thresholds in complex systems”

The philosophy behind it is explained in this paragraph:

“Our analysis focuses on the strength of the feedback between now and 2100. However, several of the feedbacks that show negligible or very small magnitude by 2100 could nevertheless be triggered well before then, and they could eventually generate significant feedback strength over longer timeframes—centuries and even millennia—and thus, influence the long-term trajectory of the Earth System. These feedback processes include permafrost thawing, decomposition of ocean methane hydrates, increased marine bacterial respiration, and loss of polar ice sheets accompanied by a rise in sea levels and potential amplification of temperature rise through changes in ocean circulation “

So - they are taking the long view. That we can take action now that would help make sure the Earth of our grandchildren and great grandchildren is much easier to manage.


This is another of their diagrams

They are saying that Earth swerved away from the glacial cycles already at the beginning when humans started to influence climate - and that if we follow what they call “Earth System Stewardship” we can guide the Earth climat system into a particularly good stable “notch” there where everything is optimal for humans and very stable for hundreds of thousands of years - but if we do not, then eventually, over the very long term, then parts of Earth get uninhabitable for humans.


As for the sea rising tens of meters, then they acknowledge this happens on very long timescales.

“A few of the changes associated with the feedbacks are reversible on short timeframes of 50–100 years (e.g., change in Arctic sea ice extent with a warming or cooling of the climate; Antarctic sea ice may be less reversible because of heat accumulation in the Southern Ocean), but most changes are largely irreversible on timeframes that matter to contemporary societies (e.g., loss of permafrost carbon). A few of the feedbacks do not have apparent thresholds (e.g., change in the land and ocean physiological carbon sinks, such as increasing carbon uptake due to the CO2 fertilization effect or decreasing uptake due to a decrease in rainfall). For some of the tipping elements, crossing the tipping point could trigger an abrupt, nonlinear response (e.g., conversion of large areas of the Amazon rainforest to a savanna or seasonally dry forest), while for others, crossing the tipping point would lead to a more gradual but self-perpetuating response (large-scale loss of permafrost). There could also be considerable lags after the crossing of a threshold, particularly for those tipping elements that involve the melting of large masses of ice. However, in some cases, ice loss can be very rapid when occurring as massive iceberg outbreaks (e.g., Heinrich Events).”

So - the melting of the Greenland ice sheet and the Antarctic ice sheet - that involves melting large masses of ice. Ice doesn’t melt easily. In the old days before refridgerators - as recently as the nineteenth century, people would collect ice in the winter, and store it underground, and it would last all summer, keeping their food cool, because ice has such a high heat capacity and doesn’t melt easily. It’s the same for Greenland and Antarctica. It is impossible for most of the ice to melt quickly.

Some of it can. The glaciers in Western Anatarctica are a particularly difficult unknown because glaciers can speed up, and rush to the sea (I mean at a snail’s pace but fast for a glacier) if there is enough of it melts to let it rise above obstacles that were stopping it before.

But the main parts of these ice sheets won’t melt for millennia, indeed, tens to hundreds of thousands of years. And the Antarctic ice sheet is actually continuing to accumulate ice at present - has done so through all the previous ice ages and interglacials.


On the sea level rise I’d like to clear up a common misconception I’ve come across, talking about this via PM’s. It will probably seem obvious once I explain it but people who are scared sometimes don’t think too clearly. Especially if you are panicking it can be hard to avoid being rather confused in your thinking.

Most of the land is a long way above sea level. Suppose for instance that the sea rises by 10 meters. It does not mean that the entire Earth, mountains and all, is covered in a layer of sea water to a depth of 10 meters. It just means that the sea rises along the sea shores of the Earth. You are only at risk from sea level rises if you are close to the sea shore or living somewhere very low lying. And the maximum sea level rises through to 2100 are only a few feet. If your house is so close to the sea that the sea gets to your front door at the very highest tides during a storm surge - then - by 2100 then depending where you live, the sea will rise to half way up your front door. The projections vary depending where you live. If you live in Greenland it is possible that the sea level actually drops (because the Greenland ice has a gravitational effect bunching the sea water around it - and as it melts the sea would recede).


The tipping points they identify wouldn’t all be triggered at once. But one after another. The first ones at 1–3 °C as this diagram shows


A lot of the articles about this have suggested it is saying the world will soon get too hot for humans.

The press release gives a quote that doesn’t seem to occur in the final paper, maybe from an earlier draft?

The press release says

A “Hothouse Earth” climate will in the long term stabilize at a global average of 4-5°C higher than pre-industrial temperatures with sea level 10-60 m higher than today, the paper says.

By long term in this context typically they mean centuries to thousands of years, could be tens or hundreds of thousands of years.

The paper itself says

“ Crossing the threshold would lead to a much higher global average temperature than any interglacial in the past 1.2 million years and to sea levels significantly higher than at any time in the Holocene.”

Then the press release has this quote from one of the co-authors

Places on Earth will become uninhabitable if “Hothouse Earth” becomes the reality," warns co-author Johan Rockström, former executive director of the Stockholm Resilience Centre and incoming co-director of the Potsdam Institute for Climate Impact Researc

This does not fit the previous quote in the press release, because 4 °C will not make places on Earth uninhabitable, or anything like.

NONE OF THE WORLD BECOMES UNINHABITABLE FOR HUMANS AT 4 °C. It actually gets more habitable if anything, especially if you can start to cultivate parts of Siberia and Canada. For more on this see

That puzzled me - but I think it is just a hastily put together press release since the supposed quote doesn’t occur in the final version of the article.

Basically the press release contradicts itself, such things can happen, some slip in copy editing.


At 7 °C some parts of the Persian gulf have occasional heat waves once a decade or so during which you have to have air conditioning to survive as a human. There is a limit to what any human can stand, however healthy you are. It is not just temperature. A combination of too hot, and the air too moist - and you will just die quickly. But with technology you can survive.

At 3–4 °C, which is within the ranage of what is possible using the climate change pledges so far - then parts of the Persian gulf will be very uncomfortable in heat waves without technology to cool you down. But not uninhabitable.

This paper from 2010 looks at the long term effects of small increases in temperature on these habitable regions, coming to the conclusion that the effects would dwarf the results of flooding, if the temperature increases reach 7 °C or higher.

"We conclude that a global-mean warming of roughly 7°C would create small zones where metabolic heat dissipation would for the first time become impossible, calling into question their suitability for human habitation. A warming of 11–12°C would expand these zones to encompass most of today’s human population. This likely overestimates what could practically be tolerated: Our limit applies to a person out of the sun, in gale-force winds, doused with water, wearing no clothing, and not working. A global-mean warming of only 3–4°C would in some locations halve the margin of safety (difference between TW max and 35°C) that now leaves room for additional burdens or limitations to cooling. Considering the impacts of heat stress that occur already, this would certainly be unpleasant and costly if not debilitating. More detailed heat stress studies incorporating physiological response characteristics and adaptations would be necessary to investigate this.

"If warmings of 10°C were really to occur in next three centuries, the area of land likely rendered uninhabitable by heat stress would dwarf that affected by rising sea level. Heat stress thus deserves more attention as a climate-change impact.

"The onset of TW max > 35 °C represents a well-defined reference point where devastating impacts on society seem assured even with adaptation efforts. This reference point contrasts with assumptions now used in integrated assessment models. Warmings of 10°C and above already occur in these models for some realizations of the future (33).

7°C is a high temperature increase, higher even than expected for "Business as usual" - RPC 8.5 in climate change jargon.

Chart from this page.

At 11–12°C then most of the areas where humans live today become uninhabitable. But even then - it does not make Earth uninhabitable. We certainly won’t go extinct.


I am not sure what they mean by “hothouse Earth” - if they mean 4–5 C then the Earth doesn’t become uninhabitable anywhere.

If they mean 10 - 11 C then places like the hottest parts of India, Southern China, Persian Gulf, the hottest parts of the Americas- they become uninhabitable.

But Canada, Alaska, Siberia - they become vast areas of agricultural land for humans. And even in the areas too hot for humans, you may have crops, maybe robot tended, or humans with air conditioning!

After all Antarctica is at present pretty much uninhabitable for humans without technology. This is a future world where places near the equator will be uninhabitable in much the same way Antarctica is today, but for different reasons.


This is a simple point but just to be clear. They are not talking about heat year round,unless you live in the equatorial regions. Areas far from the equator will still have winter and summer, as before.

The winters will be a bit warmer perhaps, but the heat waves will happen in the summer. As winter approaches, the heat waves are over. We still have winters no matter how warm it gets, because they are due to the tilt of Earth’s axis. Always going to have temperature variations between summer and winter, except at the equator and close to it.


The conclusion of hte paper is not that it is hopeless. They are arguing for carbon capture and storage. That we need to look into natural and also artificial ways of capturing carbon dioxide from the atmosphere and storing it.

“Stabilized Earth would require deep cuts in greenhouse gas emissions, protection and enhancement of biosphere carbon sinks, efforts to remove CO2 from the atmosphere, possibly solar radiation management, and adaptation to unavoidable impacts of the warming already occurring”

This is what the BBC says about it.

The only upside, if you can call it that, is that the worst impacts may not be felt for a century or two. The downside is that we wouldn't really be able to do anything about it, once it starts.

We can avoid the hothouse scenario but it's going to take a fundamental re-adjustment of our relationship with the planet.

"Climate and other global changes show us that we humans are impacting the Earth system at the global level. This means that we as a global community can also manage our relationship with the system to influence future planetary conditions.

"This study identifies some of the levers that can be used to do so," says co-author Katherine Richardson from the University of Copenhagen.

So not only are we going to have to stop burning fossil fuels by the middle of this century, we are going to have to get very busy with planting trees, protecting forests, working out how to block the Sun's rays and developing machines to suck carbon out of the air.

Risk of 'Hothouse Earth' despite CO2 cuts

This is what New Scientist says:

“The first cluster of tipping points in the climate system is centered around 2°C warming,” says team member John Schellnhuber of the Potsdam Institute for Climate Impact Research. “The perturbation could push the planetary machinery out of the glacial cycle.”

The team stress that they are pointing out a potential danger that needs study, not that they have shown conclusively that this will happen. “We are discussing a possibility, not a probability, and ask the scientific community to put our scenario to the test,” says Schellnhuber. Indeed, other climate scientists that New Scientist spoke to – who did not wish to be named – expressed scepticism at its findings although others thought it was reasonable.

Global warming may become unstoppable even if we stick to Paris target


Anyway - I think a lot of the confusion has come because it is qualitative and it doesn’t give any timescales at all. So - it is easy to agree with it if you think this domino effect will lead to a hotter Earth thousands of years into the future and will be hard to reverse and need significant mega technology over the next couple of centuries to prevent - and may be easy to prevent if we can stay within 2 °C using the methods proposed for the Paris agreement - and then combined with growing more forest and carbon capture and storage.

That I think is what it is saying myself.

If you think that it is saying that all those dominoes may tip one after another in the next century or two and that the Antarctic and Greenland ice may melt in a couple of centuries then it would seem very exaggerated indeed and rather unlikely.

Because they don’t give a timescale then people are reading it in different ways I think.

But - it is much more of a meta study - and a suggestion of things for future scientists to look into - it is not actually doing any new research as such. It is more an overview and trying to connect together different things and saying to scientists “Look at this, it’s important”.


I’d just like to say something briefly about this. You will see a lot of alarmist stuff online about clathrates destabilizing, leading to a sudden runaway greenhouse in a few decades. This is out of date research.

They look at the Siberian permafrost but not at clathrates. Nor does it appear on their map of tipping points. As with the IPCC they don’t treat it as an issue. So why is this?

First, some background, the clathrates are methane trapped in a form of ice that is stable at temperatures up to around 3 °C, in thick deposits on the Arctic sea floor.

Anyway researchers found methane seeps from the sea floor a few years back and worried that it meant the clathrates were destabilizing because of the warming Arctic ocean.

The latest research suggests it probably formed 6 million years ago. And that it started to get released 2 million years ago as the Arctic ice sheets formed - and that it has been leaking ever since. The leakes don’t actually come from the clathrates themselves but rather from deep gas fields well below the methane plumes.

Recent observations of extensive methane release from the seafloor into the ocean and atmosphere cause concern as to whether increasing air temperatures across the Arctic are causing rapid melting of natural methane hydrates. Other studies, however, indicate that methane flares released in the Arctic today were created by processes that began way back in time – during the last Ice Age.

Newest research from the Center for Arctic Gas Hydrate, Climate and Environment (CAGE) shows that methane has been leaking in the Arctic for millions of years, independent of warm or cold climate. Methane has been forming in organic carbon rich sediments below the leakage spots off the coast of western Svalbard for a period of about 6 million years (since the late Miocene). According to our models, methane flares occurred at the seafloor for the first time at around 2 million years ago; at the exact time when ice sheets started to expand in the Arctic.

The acceleration of leakage occurred when the ice sheets were big enough to erode and deliver huge amounts of sediments towards the continental slope. Methane leakage was promoted due to formation of natural gas in organic-rich sediments under heavy loads of glacial sediments. Faults and fractures opened within the Earth’s crust as a consequence of growth and decay of the massive ice masses. This brought up the gases from deeper sediments higher up towards the seafloor. These gases then fueled the gas hydrate system off the Svalbard coast for the past 2 million years. It is, to this day, controlling the leakage of methane from the seabed. BLOG: Whether warm or cold, methane keeps leaking in the Arctic

This casts it into a different light.

Their temperature fluctuation plots show that the temperature fluctuations in the ocean only get high enough to destabilize the clathrates even occasinoally, down to 1.65 meters below the sea floor,

The clathrates are destabilizing in the area shown in blue in this plot. The rest of the clathrates at depth remain at a little over 2 °C year round, not high enough to destabilize. The shaded area shows the region of temperature / depth that clathrates have to reach to destabilize. The areas that do destabilize do so only very slowly (centuries) because they are only warmed sufficiently for less than half the year - and this doesn’t seem to be enough for fast destabilizing

So their studies and models do not back up the clathrate gun hypothesis. And the original hypothesis was not based on detailed studies like this.

A USGS metastudy in 2017 by the USGS Gas Hydrates Project concluded Gas Hydrate Breakdown Unlikely to Cause Massive Greenhouse Gas Release,

“Our review is the culmination of nearly a decade of original research by the USGS, my coauthor Professor John Kessler at the University of Rochester, and many other groups in the community,” said USGS geophysicist Carolyn Ruppel, who is the paper’s lead author and oversees the USGS Gas Hydrates Project. “After so many years spent determining where gas hydrates are breaking down and measuring methane flux at the sea-air interface, we suggest that conclusive evidence for release of hydrate-related methane to the atmosphere is lacking.”

The paper itself is here: The interaction of climate change and methane hydrates.

In short, it is a hypothesis not yet supported by evidence. At one point the methane seeps seemed to be evidence, now they are not. At one point analysis of some of the previous warming events of Earth suggested it was responsible for them, now, it seems it was not. See Permian–Triassic extinction event#Methane hydrate gasification.

So - there is basically at present no reason to accept it as something that could happen.


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