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New study reconciles a dispute about how fast global warming will happen

Posted on 24 September 2018 by dana1981

We’re currently on pace to double the carbon dioxide-equivalent (including other greenhouse gases) in the atmosphere by around mid-century.  Since the late 1800s scientists have been trying to answer the question, how much global warming will that cause?

In 1979, top climate scientists led by Jule Charney published a reportestimating that if we double the amount of carbon dioxide in the atmosphere from pre-industrial levels of 280 ppm to 560 ppm, temperatures will warm by 3 ± 1.5°C.  Four decades later, ‘climate sensitivity’ estimates remain virtually unchanged, but some climate contrarians have argued that the number is at the low end of that range, around 2°C or less.

It’s an important question because if the contrarians are right, the 2°C resulting global warming would represent significantly less severe climate change consequences than if mainstream climate scientists are right and temperatures rise by 3°C.  It would also mean our remaining carbon budgetfor meeting the 2°C Paris target is about twice as large than if the mainstream consensus is right.  If the consensus is correct, we’re on pace to blow through the remaining Paris carbon budget by around 2030.

Another nail in the contrarian ‘low sensitivity’ coffin

Studies published in March 2014May 2014, and December 2015 identified two critical flaws in the contrarians’ preferred so-called ‘energy balance model’ approach: it doesn’t account for the fact that Earth’s sensitivity can change over time, for example as large ice sheets continue to melt, or that the planet responds differently to different climate ‘forcings’.

Last week, the journal Earth’s Future published a study by the University of Southampton’s Philip Goodwin that took both of these factors into account.  Goodwin ran climate model simulations treating every forcing separately, including changes in greenhouse gases, solar activity, particulates from volcanic eruptions, and from human fossil fuel combustion.  For each, he included feedbacks from changes in factors like atmospheric water vapor, clouds, snow, and sea ice, including how these factors change over different timescales, as Goodwin explained:

I ran 10 million simulations with a relatively simple climate model. These 10 million simulations each used different climate feedback strengths, and so the way that climate sensitivity responded over time was different in each simulation.  To check which of the 10 million simulations were most realistic, I checked each simulation against observations of warming in the atmosphere and ocean up to the present day. I kept only the simulations that agreed with the observations for the real world.

This left 4600 simulations, where the values of the climate sensitivity (and changes in climate sensitivity over different timescales) agree with the atmosphere and ocean warming observed so far. It is from these final 4600 simulations that evaluate how the climate sensitivity evolves over time.

Essentially, adding up all of the warming contributions from all of these factors at any given time tells us how sensitive the climate is on that timescale, whether it be a month, a year, a decade, or a century after atmospheric carbon dioxide levels have doubled. 

Over the shortest timeframes of a year or less, Goodwin found that temperatures will rise by about 2°C once carbon dioxide levels have doubled, consistent with the conclusions of the contrarian studies.  That makes sense because those studies applied current climate measurements into energy balance models, but since carbon pollution is still rising, the climate still has a large energy imbalance.  Climate sensitivity, on the other hand, is usually evaluated at the point when the Earth reaches a new energy equilibrium, long after carbon dioxide levels have stopped rising.

Once our carbon pollution levels decline close to zero (hopefully by mid-to-late century), the planet will start to reach that new equilibrium.  The slower feedbacks like melting ice will continue to kick in, and Goodwin found that on timescales close to a century thereafter, temperatures will rise by 1.9–4.6°C, most likely 2.9°C, consistent with mainstream climate science estimates since the 1979 Charney report.


 How Earth’s climate sensitivity evolves to a doubling of atmospheric carbon dioxide over different timescales, starting at close to 2°C warming and then rising to about 3°C warming after a decade. Illustration: Goodwin (2018), Earth’s Future

We need to hit the brakes or blow past Paris

In other words, we are indeed on track to burn through the remaining Paris carbon budget by 2030, and under current international climate policies, we’re most likely headed for about 3.4°C warming by 2100

Click here to read the rest

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Comments 1 to 28:

  1. 2100 isn't the endpoint, we need to be looking at where the Earth will enter into a stable balance again.

    With the feedbacks that will almost certainly result from a +3.4 Celsius increase by 2100, how much warmer will the Earth become after that. 

    The inpacts of a +3.4 C warmer Earth will be catastrophic to most life here, what if that carries through to a +12 C Earth or worse which is also possible with our current understanding.

    That will kill off all complex life on Earth taking us back to a time dominated by bacteria and viruses.

    The contrarians are almost certainly the most inaccurate at predicting outcomes with climate change because they look at the data as something to contradict not genuinely analyze.

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  2. I was thinking something similar to Doug C. We think in terms of warming projections by the year 2100, but its rather an arbitrary date related to our own lifetimes. This is natural of course, but  I think its the next 1 - 5 centuries that are crucial for humanity as a whole if one thinks in a futurist sense. Firstly its this period of about 1- 5 centuries where the full results of climate sensitivity (and climate tipping points) will be felt with sea level rise and full development of temperatures and their various consequences.

    Secondly the planet is going through a population demographic transition where the most likely track will be the current 7.6 billion people increasing to 11 billion by the year 2100, then population levelling off or possibly falling very slowly. (refer projections of population growth on wikipedia). The point is a huge population bulge of about 11 billion people from perhaps about 2100 - 2500 seems likely and will coincide with the unfolding of the worst climate impacts. Of course this is a trend based on family size, and climate change itself could well become so catastrophic that it forces population down through significantly increased mortality. Either way, its an existential threat.

    I recall reading that climate models that have best predicted the trends with clouds have high climate sensitivity. Sorry tried to find the source article but couldn't.

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  3. The simple fact is we are emitting massive amounts of the primary persistent greenhouse gas into the atmosphere every year and some are still trying to find ever more convoluted ways to justify this.

    Are Volcanoes or Humans Harder on the Atmosphere?

    "This argument that human-caused carbon emissions are merely a drop in the bucket compared to greenhouse gases generated by volcanoes has been making its way around the rumor mill for years. And while it may sound plausible, the science just doesn’t back it up.

    According to the U.S. Geological Survey (USGS), the world’s volcanoes, both on land and undersea, generate about 200 million tons of carbon dioxide (CO2) annually, while our automotive and industrial activities cause some 24 billion tons of CO2 emissions every year worldwide. Despite the arguments to the contrary, the facts speak for themselves: Greenhouse gas emissions from volcanoes comprise less than one percent of those generated by today’s human endeavors."

    If there was a supervolcano or a massive flood basalt somewhere on the Earth's surface would we be debating at all the catastrophic impacts of it emitting 100 times the average amount of CO2 from tectonic activity every year.

    We'd be preparing for the same kind of massive die-offs that the geological record indictates are associated with similar events like this in the past.

    Something we are already beginning to see on a large scale when you consider the massive and rapid die-offs on the Great Barrier Reef alone.

    This is a supervolcano we can shut of and in fact be much better for in terms of air quality, ecological integrity and financial cost.

    The Data Says Climate Change Could Cost Investors Trillions

    "If we stay on the current emissions path, the study predicts, the value at risk in global portfolios could range from about $2 trillion to $25 trillion. In a bit of understatement, Simon Dietz of the London School of Economics, the lead author of the report, told The Guardian, “long-term investors…would be better off in a low-carbon world.”

    Estimates of climate risk in the trillions are unfortunately getting more common. Last year, Citi produced a powerful study of the costs and benefits of shifting the energy system toward low-carbon technologies. Unchecked climate change, Citi said, could cost the world $72 trillion by the middle of the century. But the big surprise in Citi’s report was the cost of building the low-carbon economy: the world can spend $2 trillion less in total on energy infrastructure and ongoing fuel costs than it would in the business-as-usual scenario. So we save $2 trillion and avoid losing up to $72 trillion in economic activity."

    Fossil fuels are a lose-lose no matter how contrarians still try and load the dice in the favour of the fossil fuel sector by consistently downplaying the likely impacts of the continued emissions of tens of billions of tons of CO2 a year.

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  4. The aspirational objective of only 1.5 C warming is a key point of the Paris Agreement.

    Leaving CO2 at the level that results in 2 C warming is unacceptable. And the lack of responsible leadership means that it is highly likely that non-profitable actions to sustainably remove CO2 from the atmosphere will be required (more if the impacts exceed the 2 C limit.

    Since it is already unfair to impose the challenges of climate change on future generations (even unfair to impose 1.5 C impact), the current generation should be obliged to start un-profitably removing CO2 from the atmosphere, and back-tax the people who got wealthy undeservingly as much as possible to pay for what undeniably needs to start to be done.

    It needs to be clear that wealth will be removed from people who benefit from the burning of fossil fuels to correct the harm done. That way the entire issue is in 'Their' hands. They want more wealth from the production of more excess CO2? They can only have what is left after paying to remove excess CO2.

    Making the people who benefit from a harmful activity understand that they will be the ones to pay to fully neutralize the impacts of their pursuits, pro-rated by how much benefit they personally get, appears to be the only way those people will 'get the message'.

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  5. I agree volcanic  activity is clearly not responsible for the modern global warming period. It could only be implicated in the recent global warming period if there was some substantial change in volcanic activity in recent decades compared to earlier decades. Given the quantities of CO2 emitted by volcanoes are quite small compared to human emissions, according to sources mentioned above, there would need to be a very substantial and obvious change.

    A quick look at "list of large volcanic eruptions of the 20th century" on wikipedia shows no obvious change in activity between the early part of the 20th century, and the part after 1975 when the "modern" warming period related strongly to CO2 emissions started.  Ditto theres no difference in volcanic activity overall between the 19th and 20th centuries. Yes its eyeballing a list but that is sufficient in this case.

    This is reasonably basic detective work, so the fact that the "denialists" don't register it looks like wilful ignorance to me in many cases. Head in the sand stuff. I'm so sick and tired of it. We should be able to have grown up conversation with this obvious material on the table, and not disputed and ignored. I'm all for genuine scepticism if its intelligent and evidence based, but I haven't seen any for years now.

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  6. Doug_C @1,
    The bleak future you paint for AGW is not one I see.
    ♦ Firstly, "a +3.4ºC warmer Earth" mentioned in the OP says its based on this which is the projected warming if we restrict our mitigation to 'current policies'. As the world ramps up its mitigation, that projected value will drop.
    ♦ Secondly, you do not set out the "current understanding" which you say demonstrates a possible +12ºC world. I am not aware of research that shows such warming (without unmitigated emissions continuing). Mind, I would add that there is much research to suggest that "a +3.4ºC warmer Earth" would come with added bonus warming from natural feedbacks which science cannot/doesn't yet quantify and even if there were no added bonus warming, "a +3.4ºC warmer Earth" is still not a good place to be.
    ♦ Thirdly, when it comes to that "stable balance" in global temperatures at the end of the AGW process, the forcing from CO2 & other GHGs will be in decline well before we reach the equilibrium temperature of our peak forcing. Indeed, with zero emissions the forcing level will be dropping fast enough to pretty-much cancel-out temperature rise. (Note, we will still be left with half our CO2 and thus more than half our CO2-forcing at the end of the coming millenium unless future generations act the reduce it further.)
    ♦ Fourthly, it is probably the sea-level rise that sets a limit for long-term AGW. I am always a bit pigged-off by SLR being only projected to 2100 rather than shown on a multi-century basis. IPCC AR5 SPM E.6 doesn't once countenance the problems of SLR post-2100. You have to dig a lot deeper to see what lies in store. You find Fig IPCC AR5 Fig 13.14 (pasted below) showing that even a +1.0ºC warmer Earth will experience multi-metre SLR which our decendants may prefer not to experience. (In 13.14, the left-hand graphics are 'multi-millenual', the right-hand SLR after 2000 years, respectively for thermal expansion, glaciers, Greenland, Antarctica, total.) And note the 7-metre rise caused by Greenland going into melt-down in a +1.5ºC world, a process which will become irreversible if it gets the chance. AR5 rather plays down the chances of any surprises from Antarctica in a sub+4.0ºC world but the message from Greenland is shocking enough.

    AR5 FIG13.14

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  7. nigelj @2,
    The paper you perhaps recall saying that the models best at reproducing the climate have higher climate sensitivity due to clouds was likely Brown & Caldeira (2017) which I've not seen in full but lead-author Patrick Brown has a useful post on his website about it.

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  8. 2°C are almost impossible as temps have already risen by 1.2 degrees at 405 ppm CO2.

    Scratching the 1.5°C Jazz

    => Scratching the 1.5°C Jazz

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    Moderator Response:

    [DB] Shortened image width to 450, as it was breaking page formatting.  Please be mindful of this in the future.

  9. SirCharles,

    It is undeniable that non-profitable removal of CO2 from the atmosphere, starting now, will be required to limit the harm done to the future of humanity.

    The more important understanding is that minimizing the harm done to the future of humanity by the 'people pursuing the Best Possible Present for Themselves any way they can get away with' will require a significant correction of the incorrectly developed socioeconomic-political games that people play.

    If the systems are not corrected the developed results will be more harmful to the future of humanity, and in many more ways that the impacts of the production of excess CO2 from the burning up of non-renewable buried ancient hydrocarbons.

    A caring and considerate portion of the population will not be able to overcome the damage done by 'those who care less and can get a competitive advantage in the competitions to appear to be superior relative to others by behaving less responsibly (more harmfully)'.

    The systems need to change in ways that ensure that 'improved awareness and understanding of what is going on and the application of that knowledge to develop a sustainable and improving future for humanity' Governs the actions of everyone (the key part of the word Government).

    And the thing that pursuers of personal liberty and smaller government appear to deliberately fail to understand is that 'the more people who self-govern more altruistically, the smaller the Government (the collective actions to limit the people who do not responsibly self-govern) will need to be'. And that increased proportion of altruistic power and wealth has to happen first - only then can Government get smaller. And until that imrpoved behaviour occurs in the general population and business world, the Government (of the people, by the people, for the people) must be ruled by caring, considerate, thoughtful altruistic people responsibly limiting what is gotten away with in the games people play.

    Right now many of the supposedly most advanced nations are struggling to have the type of leadership that the future of humanity clearly requires. Some of the less developed nations appear to be getting more responsible leadership.

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  10. MA Rodger @6

    1. I'm not looking at a bleak future, I'm looking at a very disturbing present, catastrophic climate change isn't soemthing that is going to hit at some undefined point in the distant future it is here now. What does an almost complete loss of coral reef systems alone mean to an overall ecological integrity, something that is almost inevitable now with the decades of warming already locked in with the CO2 we've already emitted. Every extra year of emissions is locking in futher warming years down the road. I'm very concerned about what is already happening with a full expectation it will get much worse even if we fundamentally changed course today which we have not.

    2. I'm going by what researchers like James Hansen have to say and acknowledging that much of research is conservative when compared to what we are actually seeing in a real world response. Whether it is ice loss, changing climate patterns and more. And some of them have made it clear they expect far more warming than the current predictions are estimating.

    3. As long as we are emitting billions of tons of CO2 a year the positive forcing will continue, some nations like the one I live in are still projecting decades of large scale fossil fuel use. The Canadian federal government just spent $4.5 billion dollars to buy a dilbit pipeline to enable a tripling of capacity of this one line of one of the most carbon intensive fossil fuels there is, oil sands bitumen. There is not going to be any leveling off of the radiative forcing of CO2 as long as we are rapidly increasing atmospheric levels of CO2 by burning fuels like oil sands bitumen. And the lag in ocean warming means that the CO2 we emit today is not going to be rebalanced for decades.

    4. It's not sea level rise that is going to set a long term limit on human forved climate change, it is going to be a thermal equilibrium in the oceans that will take centuries to establish based on the radiative forcing we have already created. The oceans are the main driver for climate and the main mechanism to move heat around the planet. This means there will be no such thing as stable weather and climatic conditions until this adjustment is completed. That alone is going to be a major stressor on people and entire biotas for those centuries.

    We are messing with one of the fundamental factors that makes life possible on Earth in a way that assumes we are in control of this incedibly powerful mechanism.

    I see no signs at all we are, the only choice we have now is how far we are willing to push it to cross tipping points some of which we almost certainly have not been able to define in any meaningful way yet.

    It's Russian Roulette on a planetary scale, so yes, I am very concerned.


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  11. A most interesting analysis but possibly of acedemic interest.  If we trigger a tipping point, all bets are off.  The one we seem to be most worried about at present is starting to release the huge reserves of methane locked in clathrates.  Indeed, this seems to be under way in the Arctic both on land and sea bottom.  At some point this is likely to become self perpetuating and some research suggests that such an event in the past led to sudden and extreme changes in the climate.  It has now been 55m years since the PETM so lots of time for clathrates to have accumulated.  Since there seems no reasonable chance that we will significantly reduce our carbon output any time soon, we are pushing this experiment to the limit.

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  12. MAR @7, thank's, but it wasn't that research. I remember now it was this article on page 22 as follows:

    Fasullo and Trenberth found that the climate models that
    most accurately capture observed relative humidity
    in the tropics and subtropics and associated clouds
    were among those with a higher sensitivity of
    around 4°C. 64 Sherwood et al. also found a
    sensitivity figure of greater than 3°C.65 Zhai et al.
    found that climate models that are consistent with
    the observed seasonal variation of low-altitude
    marine clouds have an average sensitivity of
    3.9°C. 66 Recently it has been demonstrated the
    models that best capture current conditions have
    a mean value of 3.7°C compared to 3.1°C by the
    raw model projections.67

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  13. DougC @10

    "I'm going by what researchers like James Hansen have to say and acknowledging that much of research is conservative when compared to what we are actually seeing in a real world response."

    The following article called "what lies beneath, the understatement of existential climate risk" may be of interest. 

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  14. william @11

    There are many unknowns with the methane clathrate gun hypothesis, one thing we don't want to find out is we got it wrong in predicting when it goes off and how much methane is released.

    Billions of tons of methane being added in pulses to the atmosphere is a nightmare forcing we really don't want to see.

    And it's hard to see how some of these deposits are going to remain stable as the temperature continues to climb in critical locations like the Arctic. It has happened before.

    Ancient methane 'burp' points to climate change 110 million years ago

    "The thawing of the so-called methane hydrates coincides with a period of warming following a volcanic eruption, which released a cloud of carbon dioxide into the atmosphere.

    "That was when Earth transitioned from a cold climate to a warm climate," Grasby said.

    "So we see this sudden and short term release of methane is coincident with this period of global climate warming.""

    There's some question about how much of this methane would get into the atmosphere, but there is also isotopic evidence that methane pulses have played a significant role in previous rapid warming periods that have resulted in extinction level events like the End Permian.

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  15. Here's bit on the isotopic evidence of the role than methane clathrates can play in this kind of scenario, the risk is very real.

    Carbon isotopic evidence for terminal-Permian methane outbursts

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  16. Doug_C @7,
    I have to contradict you and pretty-much refute everything you say.

    Homing in on two parts of your reply:-
    ♦ It is indeed a future you discuss, not the present. What did James Hansen say to the media just a few months ago? “It’s not too late,” Hansen stressed. “There is a rate of reduction that’s feasible to stay well below 2C. But you just need that price on carbon.”
    Sorry! Correction. Hansen didn't 'say' it, he 'stressed' it!
    ♦ Climate forcing is not "locked in" and as a result the global warming is also not "locked in."
    To be more precise, the majority of today's climate forcing is not locked.
    Consider this. If we stop emitting today, the oceans will continue to absorb our CO2 as there will be waters that have not seen the light of day for centuries continuing to return to the surface and absorb CO2. After 100 years of zero net emissions, today's 410ppm CO2 levels would be down to something like 370ppm and in 1,000 years would be down to something like 355ppm. (And there it would remain for many thousands of years as the oceans would have then come into CO2 equilibrium and we would be reliant on geological processes for any further natural reductions.) This is why RCP2.6 is projected to result in peak temperatures by mid-century which coincidental with the climate forcing peaking.IPCC AR% Fig 12.05

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  17. MAR @16, I wonder if you are misinterpreting some of the comments posted by DougC. While he suggested various possible extreme scenarios, I did not see him suggesting such things are locked in already, and that we shouldnt or can't do anything to stop global warming.

    And his suggestion that 12 degrees was possible may not be far from the truth. According to the research quoted in this article, burning all fossil fuels on the planet could cause warming approaching that level to quote "Global average temperatures would soar by 10C (50F), while the arctic, where temperatures in February year were already 16C above average, could see temperatures soar by 20C, researchers found." Of course this would require literally burning all the oil and coal on the planet, and would take several centuries and hopefully humanity isn't that stupid. 

    Even if we dont burn all fossil fuels on the planet,  feedbacks could push warming to about 8 degrees before things stabilise.

    Having said all that, your technical commentary on warming, Hansens views, etc looks entirely accurate and interesting to me, as are your comments on feedbacks, black carbon and sea level at RC. I certainly would agree we are still in a position to greatly improve outcomes, by appropriate emissions cuts and so on.

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  18. nigelj @17,
    You are correct about the +12ºC world being possible. Indeed, the graphic @6 shows RCP8.5 could reach such a level of warming (showing global temperature relative to 1986–2005 so add another +0.6ºC to make it relative to the 1800s).
    But note this graph is not showing a follow-on from "a +3.4ºC warmer Earth" after 2100, and I say this not because RCP8.5 is a tad warmer in 2100. (The graphic is showing +3.7ºC or +4.3ºC above the 1800s.) The graphic shows +12ºC not because of follow-on but because RCP8.5 includes accelerating forcing through to 2100 when the forcing-deceleration begins. By 2150, the additional annual forcing is still up at the level we see today.
    Of course, there are feedbacks not modelled in these GCM-generated projections which was perhaps the thrust of the speculation @1. Yet the assessment leading to the +12ºC, any study of what these feedbacks will bring; that remains unmentioned. (Indeed, so too does your "about 8 degrees before things stabilise.")

    I'm always happy to re-appraise both my understanding of stuff and my writing in comment threads. I'm happy to amend that understanding and set out corrects to my comments, although I would not rate the humble pie of admiting-error as a happy thing.

    Doug_C @1 presents five paragraphs. I agree with the first and the last. Indeed I strongly advocate the message of the first but apparently for different reasons than those given by Doug_C, reasons he sets out in the middle three paragraphs.

    The second paragraph @1 is just a question but does imply "a +3.4ºC warmer Earth" is where we are going. My response @6 only points to the basis of "a +3.4ºC warmer Earth" and how humanity can (& will) do better. Perhaps I can add strength to that referencing of the basis of "a +3.4ºC warmer Earth" by quoting from that source. "While the challenges are significant, limiting warming to below 1.5°C by the end of the century is still feasible from current emissions levels. However, with every decade lost, these challenges and costs rise and will, at some point, become insurmountable with warming locked in to 1.5 or 2°C and above."
    My referencing @6 (I can but assume) led on to (1)@10 which is saying the issue is the present and that our future climate is being "locked in". Again the implication is that "a +3.4ºC warmer Earth" has been locked in. I rebut this idea forcefully @16. (There is also in (1)@10 an assessment of present AGW being "concerning" and "very disturbing" but, as I read (1)@10, this isn't the issue.)

    The third paragraph @1 says that "a +3.4ºC warmer Earth" will be bad (& I agree wholeheartedly) but that it could 'carry through' to a +12ºC world. So @6 I ask for the basis of this 'carry through' to a +12ºC world. Sadly, the response (2)@10 is vague, pointing just to "researchers like James Hansen" and "some of them." The response also talks of "much of the research" being "conservative" which is the sort of non-specif comment I truly hate. It gives license to ignore research and is thus anti-scientific. More usually the "conservative" label is attached to the IPCC assessment reports which again as a generalisation is anti-scientific.
    But in all this the +12ºC world is evidently speculation. There is some room for doubt with the meaning of the +3.4ºC world although the implication (apparently strong implication) is that @1 it is being predicted as our future.

    The fourth paragraph is surely flat wrong, even with the "complex life" being undefined. Is it actually saying that a +12ºC world would see the extinction of all eucaryotes, all mushrooms plants & animals? Or just all multi-cellular organisms? The palaeoclimate has certainly seen life survive across a +6ºC world. The speed of AGW will be devastating for natural ecosystems but to suggest a +12ºC world would kill off all complex life is surely wrong. No pockets of survivable climate, anywhere? (And that is ignoring human ingenuity finding a way to survive in such a world.)
    Saying that, there are analyses describing the danger of extinction, as seen in the five previous mass extinctions, comes not directly from a climate change caused by some catastrophy but from from the impacts of the resulting unleashed procaryotes, the bacteria.

    And so, have I earned a serving of humble pie? Even a small serving? I don't see it myself.

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  19. MAR @18, I interpreted DougC's comments @ 1 and elsewehere a little differently to you in some regards. However having read his comments again, I can see how they could be interpreted in the way you say. Perhaps they lacked a little clarity, but it is probably time pressure and he makes some good points, and does better than some people I can think of over at RC with their confused pessimistic rants.

    He does indeed say a 3.4 degree warmer world is where we are going but I took this to mean if we are stupid enough to keep burning fossil fuels, surely a non controversial and self evident statement? But in hindsight, he could have helped his case if he had stated if we continue on business as usual scenario.

    Unfortunately one of the denialist tricks is to post comments that we are doomed because warming is locked in, so theres no point doing anything. Doug isn't in that category, but I guess some people could interpret his comments that way and I guess this is what bothers you? Its something we all need to be aware of anyway.

    I agree he was vague about how we get to a 12 degree world. But his sentiment was correct, and at least he wasn't claiming it could happen in our lifetimes as a couple of people have suggested.

    You say "The response also talks of "much of the research" being "conservative" which is the sort of non-specif comment I truly hate. It gives license to ignore research and is thus anti-scientific. More usually the "conservative" label is attached to the IPCC assessment reports which again as a generalisation is anti-scientific."

    Now I agree totally here, and feel the need to do a bit of a rant. Imho this all creates doubt and confusion about the research in the publics mind and undermines the credibility of the IPCC with the public. I wish people would word their criticisms a little more artfully and with some context or proviso's. In fact I dont see any evidence that the climate research is "conservative" in terms of specific papers, and at most one could argue that the conclusions the IPCC reach having reviewed all the papers are a little conservative, but this is not actually a bad thing, and I dont see it being "hugely" conservative.

    The problem is more in the summary for policy makers, where some things appear to be left out or language watered down and imho its a serious concern. The same applies to this new report on paris timeframe issues.  I hope you see this and enough links have been posted on the issues. It probably reflects trying to get agreement of multiple countries and their representatives, so its essentially political and is not an understatement of scientific knowledge, but that doesn't in any way justify it. The document ends up potentially creating a false impression and understating risks.

    It is however a tough problem to solve. Like herding cats. However it's certainly not a reason to rubbish the entire IPCC reports or climate research, because once we do this we play right into the deniliasts hands because its music to their ears.

    So on balance I do think there are some valid criticisms of the IPCC summary for policy makers, and things of a similar nature, but they need to be worded carefully, not in the brainless, emotive and naive way the usual suspects do. I think you yourself have bemoaned the lack of attention given to long term sea level rise.

    Regarding the killing of all complex life. He should probably have said something like "all or most complex life". However I think for the purposes of his comment the definition of complex life is self evident enough.

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  20. MAR @18, just filling in a gap in my own comments: "(Indeed, so too does your "about 8 degrees before things stabilise.") Study here.

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  21. nigelj @20,

    Chucking a few more words into that "gap", the "Study here" you link to (Note the "3.6 degrees" is Fahrenheit) is based on Steffen et al (2018) which I think is doing some good work but perhaps is not presenting a scientific message or presenitng it as clearly as it should. The actual paper itself spends too long in systems-analytical mode and so you have to delve into the Supporting Information to find quantifiable findings. If you add up the numbers in Table S2, it presents a potential additional 0.5°C of warming in a +2°C warmed world by 2100 resulting from all the extras not included in the GCMs. That 'additional' figure would presumably be bigger if it was assessed for 2200.

    I see two issues here. Firstly, how good is that 0.5°C estimate of additional warming at +2°C? Half of the 0.5°C is made up of melting permafrost emissions which helps simplify the analysis a bit. There has been over the last year a few papers suggesting that it is a +1.5°C that will trigger the bulk of the +2°C permafrost feedback. Mind, I do think these studies concentration on emissions which is just one side of the story. With all this thawing, there is also the spread of plant growth as high latitude lands warm. Steffen et al would do well if it prompted scientific discussion of the size of natural feedbacks under the sorts of warming humanity is hoping to keep to.

    The second issue is probably that "8 degrees" issue. If we do over-run the Paris limits, how bad can it get? The "3.4°C warming by 2100" mentioned in the OP, the level of AGW suggested by GCMs if the current commitments made by nations are fulfilled and no more. My own view is that we don't want to be going anywhere as awful as a +3.4°C world, but if we did provide that level of forcing to achieve it, how much extra could we expect? How strong do feedbacks become if we over-run Paris?

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  22. MA Rodger @21

    Thank's for the research links. I have read both and they are mighty interesting reading, although a lot to absorb, and I agree they leave some things unclear, and I think they leave questions unanswered as to how fast a hothouse earth might happen, other than a vague note about possibly a couple of centuries, but it's still a genuinely alarming statement. So is the 12 degrees in your IPCC emissions profiles table if we just go on burning fossil fuels.

    I do wish Americans would use celsius. Its very confusing using fahrenheit.

    "Firstly, how good is that 0.5°C estimate of additional warming at +2°C? "

    I assume you are suggesting forests spreading northwards would stabilise soils and absorb CO2. Interesting thought, and its not clear to me if they considered this. However the CO2 is plantfood effect is supposed to saturate fairly quickly or cancel out, because warming also affects photosynthesis and other soil processes and it intuitively seems to me that the march of forests northwards would tend to lag behind areas of thawing permafrost, but the question would be how much. They didn't really say. But it was apparently not enough to stop the earth entering past houshouse conditions assuming there were substantial areas of permafrost soils, so perhaps their 0.5 degree estimate is not far off the reality.

    The map in the research suggests total melt of permafrost is not locked in until about 5 degrees, which gives some hope because its this sort of CO2 feedback and consequent warming which really will spin us towards a hothouse earth in terms of temperature and thus horrendously extreme weather, although according to the study total ice melt will be locked in well before we hit 5 degrees. Hope in the sense that we could avoid the worst of the permafrost issue if we reduced emissions promtly to Paris time goals.

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  23. MARodger @21, just a couple more comments on your comments.

    "The second issue is probably that "8 degrees" issue. If we do over-run the Paris limits, how bad can it get? The "3.4°C warming by 2100" mentioned in the OP, the level of AGW suggested by GCMs if the current commitments made by nations are fulfilled and no more. My own view is that we don't want to be going anywhere as awful as a +3.4°C world, but if we did provide that level of forcing to achieve it, how much extra could we expect? How strong do feedbacks become if we over-run Paris?"

    No I agree we dont want to get anywhere near 3.4 degrees. I don't know how strong feedbacks would become precisely, but I would think feedbacks are non linear in nature, but I havent seen a graph of how it would go. Melting permafrost reinforcing levels of atmospheric CO2 sounds rather like a run away effect like an oscillating electrical circuit, but I think it still takes time for soils (and ice) to melt even under heavy warming. Everything I have read suggests sea level rise 10 - 20 metres will take well over 2 centuries but other things may not - like abrupt shifts in global weather patterns for example and they look like they will be chnages for the worse.

    But reagrdless of all this, warming feedbacks levels could still destabilse eastern antarctica, and this could lead to sea level rise of about 2 metres per century even possibly this century, and to me this is the thing that is particularly worrying because of the rate of change. And such an elevation in temperatures could possibly cause a rapid and sudden change in atmposheric circulation on decadal to century length time frames, from what I have read.

    Even at our current 1 degree and 400 ppm of CO2 we appear commited to pliocene conditions of 3 degrees ultimately and about 10 metres of sea level rise (sort of a partial hothouse) but is something humanity coulod adapt to without massive pain. Imho anything more than 2 degrees is unthinkable in terms of scale and pain even if it takes many centuries to unfold. 

    I do see quite a lot of doomery coming, but I refuse to be a cynical pessimist, because that can be pointless. I think theres still much humanity could do to greatly reduce all these various dire possibilities. 

    Somebody said when in doubt or arguing about stuff, go back and look at the basic data. The stuff we are really sure about. The basic paleo climate data says that if we don't meet Paris goals, a serious hothouse earth is quite probable, and I think we can be reasonably sure at least some elements of it will be felt over the next couple of centuries, and  right now global temperatures in the GISS and Hadcrut datasets are tracking quite close to model estimates. These are huge flashing red lights, to my way of thinking.

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  24. nigelj @22,

    The particular point I was considering with my comment @21 "the spread of plant growth as high latitude lands warm"  was less about bigger forests and more about the convertion of the frozen permafrost land into biologically productive land.

    The permafrost is seen as being a serious problem under a warming climate because it contains large carbon stocks.  Hugelius et al (2014) put it as 300Gt(C) in shallow soils and 800Gt(C) in deep soils (and that a downward revision on previous estimates, athough you can then find Shelef et al (2017) who argue for a possible upward revision, up to 600Gt(C) on top again). By comparison, the Amazon carbon stocks (also at risk of being destabalised with AGW) are considered to be much smaller - 200Gt(C). While not all this permafrost carbon will be melted-out and then enter the atmosphere, the large numbers are a worry.

    Yet there is work that shows only a small percentage of the frozen carbon entering the atmosphere. Schuur et al (2009) shows much of the carbon released from frozen soils is matched by carbon captured by those same soils. Thus Schuur et al speculate that only 9% to 13% of the thawed soil's carbon will add to global CO2 emissions.

    Of course, the possibility that significant proportions of that carbon appears as CH4 would add to the warming potential of the released carbon.

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  25. MA Rodger @22, the Schuur link didnt work, but I found a copy of the abstract. I think what we have going on is positive feedbacks with melting permafrost, counter balanced by negative feedbacks where carbon is captured by increased plant growth, but this in turn reaches limiting factors because warming can decrease photosynthesis like a cascade of feedbacks.  Its for these sorts of reasons why I intuitively feel that climate change will be bad, but not quite as off the scale as the usual suspects over at RC think, because basically they dont think. However I'm no biologist either, so this is speculation on my part.

    But people are growing vegetables in the tundra in this article  (as it thaws) which certainly reinforces your comments.

    Yet we are left with the methane problem, although currently the global increase in atmospheric methane appears related to the tropics, with no evident spike in the tundra regions.

    I think theres an emotive component to this, where theres clearly a problem with permafrost that I believe is hundreds of metres deep in places, and so theres huge potential for a powerful positive feedback that is truly scary, we should be scared,  but we have to also calmly ask how would this actually play out? What is the likely rate of release? The evidence appears to suggest its quite slow, but the periods of hothouse earth suggest an awful lot could melt eventually and become self reinforcing.

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  26. MAR @24, this review is interesting related to the recent increase in atmospheric methane levels. It is almost like a curved ball in that the permafrost is not turning out to be the problem at least in the short term, and instead the tropics are. Expect more curved balls from the climate.

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  27. nigelj @25,

    The Schurr et al link @24 works okay for me. However ResearchGate provide a PDF download and also ReadCube (which only provide full sight of the first page) provide a link to the Supplimentary Information.

    The NASA page you link to @26 presents well the findings of the likes of Schaefer et al (2016). This perhaps fits with the idea that the tropical wetlands will be more of a future problem regarding methane emissions than will the Arctic emissions, as found by Comyn-Platt et al (2018) who calculated the Arctic methane emissions would be 25% to 30% that of the wetlands emissions.

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  28. MAR @27, thanks for the research link.  The did quite a good overview of this methane issue as below. If you dont subscribe to this pay to read publication, you can get a few article for free each months like this one on methane if you register with the website.

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