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The 1.5 degrees goal: Beware of unintended consequences

Posted on 11 January 2022 by Guest Author

This is a re-post from Yale Climate Connections by Richard RichelsHenry JacobyBenjamin Santer, and Gary Yohe

“Keep 1.5 alive” emerged as the haunting refrain of the recent United Nations climate conference in Glasgow. Although a well-intentioned rallying cry, it raises important questions about how the chant is to be interpreted. Unfortunately, 1.5° centigrade is often presented as an immutable crisis point, rooted in established scientific consensus. It’s implied that beyond this point, climate-induced damages increase dramatically.

Given the prospect that the 1.5°C target may not be met, proponents might come to rue their choice of mantra. Not only will it likely cause unnecessary despair, but oversimplification of the underlying science provides those resolutely opposed to acting on climate change with opportunities for further mischief.

This is not to argue that danger points don’t exist. There is ample evidence in paleoclimate records of sudden and dramatic shifts in Earth’s climate system, though the conditions that triggered them are not fully understood and are not directly comparable to present-day conditions.

Another reason for concern comes from computer models of the climate system. Models also alert us to the possibility that continued warming may cause rapid climate changes that cannot be easily reversed for centuries or longer. Examples of such changes include abrupt sea-level rise and slowing or even shutdown of a key part of the ocean’s system for circulating heat. While few studies suggest that these changes are imminent, models and “deep time” climate records both tell us that somewhere out there, beyond the 1.1°C of warming experienced to date, dangerous tipping points exist. We don’t know exactly where they are, just that further warming makes it more likely we will cross them.

This understanding often contrasts sharply with the statements made by public officials and the press. For example, United Nations Secretary-General Guterres implicitly attributes the politically-set 1.5°C temperature target to the science. He refers to the 2021 release of the Physical Science section of the latest IPCC Assessment Report as a “code red for humanity” and notes that “The internationally agreed threshold of 1.5°C is perilously close.” But nowhere does the IPCC special report on the impacts of 1.5°C warming suggest that a critical, well-established threshold exists at that precise level of warming: It simply concludes that limiting warming to 1.5°C, if it could be achieved, would be better than limiting warming to 2°C.

Likewise, climate stories in the news media commonly refer to a 1.5°C critical threshold beyond which the planet will experience increasingly deadly floods, wildfires, and enormous storms – and then add “scientists say.”  Crediting the climate science with establishing a specific damage threshold at 1.5°C of warming, which scientists did not do, risks erosion of public trust in their work. It also provides ammunition for those who would criticize the scientific enterprise for hyping the issue, or for using scare tactics that go beyond the available evidence.

Limiting global warming to 1.5°C is a daunting task. The climate system has not fully adjusted to the levels of greenhouse gases currently in the atmosphere, so some additional warming is already baked in, even if all emissions were to cease overnight.

There are also inherent impediments to how quickly existing energy-producing systems and capital stock (power plants, transport, and buildings) can be replaced or renovated to create nonpolluting alternatives. Together, these lags – in both the physical and human systems – suggest that 1.5°C may well already be in the rearview mirror.

Strong language, metaphors understandable … but carry risks

These are dramatic times for Earth’s climate. It is not surprising that those trying to spur public effort to counter the real and serious threat of global climate change use dramatic language and metaphors, try to anchor political targets in scientific proof, and stress frightening consequences of inaction. But motivating action on climate change is a delicate undertaking. While the scale of coming climate damage clearly calls for urgent action to transform the energy economy, there are risks in painting too bleak a picture of the challenge, and in presenting 1.5°C as the well-established climate equivalent of an end-of-the-world prediction.

One must be aware of the possibility of unintended and unwanted consequences: Paralysis and despair may arise if millions believe that exceeding the 1.5°C target inevitably signals climate Armageddon, beyond which all is lost. Such despair would imperil the continued energy and attention needed to sustain the global effort to cut greenhouse emissions.

While useful as a spur to action, “Keeping 1.5 Alive” must not be allowed to obscure the fact that it’s worth fighting to prevent every 0.1°C of additional warming – up to and (importantly!) beyond 1.5°C. And that every 0.1°C of warming avoided is cause for celebration and hope.

Richard Richels directed climate change research at the Electric Power Research Institute (EPRI). He served on the National Assessment Synthesis Team for the first U.S. National Climate Assessment and as lead author for multiple chapters for the IPCC from 1992 through 2014.

Henry D. Jacoby is the William F. Pounds Professor of Management, Emeritus in the M.I.T. Sloan School of Management and former co-director of the M.I.T. Joint Program on the Science and Policy of Global Change.

Ben Santer is a climate scientist and John D. and Catherine T. MacArthur Fellow. He was also the lead author of Chapter 8 of the 1995 IPCC report and has been a contributor to all six IPCC reports.

Gary Yohe is the Huffington Foundation Professor of Economics and Environmental Studies, Emeritus, at Wesleyan University in Connecticut. He served as convening lead author for multiple chapters and the Synthesis Report for the IPCC from 1990 through 2014 and was vice-chair of the Third US National Climate Assessment.

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Comments 1 to 19:

  1. dammit had a comment typed in and it disappeared.  Don't know what I did wrong.

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  2. The authors point to "...existing energy producing systems and capital stock", which are only half the problem.  The other half of the TWO LEADING PROBLEMS of GHG emissions is Industrial Animal Agriculture.  These authors are silent on this topic (?)  Further, GGEs should occupy only a small space alloted to the topic of environmental/ecological damage. Deforestation, desertification, excess fresh water useage, wildlife habitat destruction/extinction, widespread land use conversions for the support of animal agriculture, eutrophication of fresh and saltwaters, human diseases connected to domestic livestock, herbicides, pesticides, chemical exceedingly long list of eco-distructive activities and behaviors that may not materially affect the quantity of GGEs in the atmosphere, but even at 270 or 350ppm, (now long gone) would dangerously affect the future welfare of living things...especially humans.    

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  3. Hal Kantrud....happens to me, occasionally...don't know why.

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  4. Did we not create the greenhouse gas blanket by mining the soil for carbon during the last ten millennia, mostly from the perennial grasslands, the old "land of milk and honey"? I think a strong case can be made that the post-Industrial Revolution spike in atmospheric carbon dioxide resulted as much or more from the conversion of the New World grasslands to cropland and pasture than to the energy sources used for that effort. After all, in many areas, the plows were pulled by humans, then animals, then wood and coal for the steam engines, and only recently by petroleum.

    We transferred most of the carbon to the oceans, rivers, and wetlands, so perhaps we should begin a retrieval effort to begin rebuilding soil carbon. Since we still rely on carbon remaining in the former perennial grasslands to feed ourselves, perhaps we should consider planting perennial grasses in areas where carbon has been most severely depleted such as former forests, shrublands, and deserts. Planting trees and injecting carbon deep underground makes little sense to me

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  5. Swampfox & Hal Kantrud  ~ yes, I've had a comment, on various occasions, simply disappear when I press the Enter button.

    Almost always, it has happened when I've taken my time to type up a comment.  If say, I'm interrupted during the typing-up . . . or if I've taken my time to arrange and consider/review my wording . . . plus proofreading, etc.

    My impression is (for my case) that it is a "timing-out" problem.  If that's all it is  ~  then I hope the Administrator will consider lengthening the available window.

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    Moderator Response:

    [BL]. Yes there is a time limit on logins. If no activity is detected, you are automatically logged out. Typing in the comments box does not seem to be considered "activity".

    If this is what is happening, you will find that your typed comment has disappeared and you are no longer logged in after you click "submit".

    I do not know what the time limit is, but  I can try to find out.

    As a workaround to prevent the problem, there are a few choices:

    1. Open a second tab with a Skeptical Science page in it. You will see that you are already logged in. Periodically refresh that page (or click to another Skeptical Science page) and your session will stay active.
    2. Prepare long comments in a text editor, and then paste them into the comment box when you are ready for final editing. Avoid a word processor, as they tend to include a lot of html junk that is hidden from you in the copy/paste process.
    3. Before clicking submit, select all the text in the comment box, and copy/paste it into a word processoor text editor. If the "submit" fails, at least you don't have to start over.


  6. Hal, the IPCC report  estimate the contribution from land use change but they have wide error bars. However, carbon from soils has a different isotopic composition from carbon from fossil fuels. The build up of CO2 in the atmosphere is consistant with largely FF source. Some more details here.

    However, increasing soil carbon reserves is a useful (in many ways) mitigation strategy.

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  7. (A)  Yes, thanks BL   ~ those are useful tips.

    I hadn't gotten round to using a copy/paste using Word or similar: nor was I aware of the potential of the "html junk" problem.

    My assumption had been that the "time out" was relating to activity within the comment box itself.  But if it's just a matter of refreshing the whole page, then that is easier to deal with.

    Nevertheless, the Alexandrian solution is to extend the qualifying period.

    (B)  As Scaddenp points out, increasing the soil carbon is excellent in many ways.  Like AGW, the soil quality degradation seems a gradual "non-urgent" problem that we really should be tackling seriously.

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    Moderator Response:

    [BL] The catch is that typing in the comments box is just filling out a box provided by your browser. It isn't until you click "submit" that your browser posts the text you have typed to the server, and the server has a chance to think "oh, an active session".

    If you refresh the page with the comment box you are working in, the browser tells the server "send me that page again", and the server (which knows nothing about what you typed in the box) will send you an updated page - with another empty comments box again.

    I have been told that if you click "submit" and your comment disappears, you can use the "back" button on your browser to get back to the version of the page with your text in the box. At that point, you could copy the contents, paste elsewhere, log back in, and continue.

    To keep your session active, and keep the contents of your comments box intact, you need to interact with using another tab or window. The activity in the other tab will extend the timeout for all tabs/windows connected to


  8. So did burning fuels create most of the greenhouse gas blanket? I would guess there are significant lag times but are there long-term temperature data that generally follow the long-term increase in atmospheric CO2? If they increase together, the recent spikes look small compared to the long term trends.

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  9. Hal Kantrud @8  ~ your meaning does not come through very clearly, at all. Do you mean long term periods as decades, or mega-years?  What are these spikes (plural) that you are referring to?  Clarity of explanation would be most welcome!  Indeed, essential.

    (b)  Thanks once again, Bob  Loblaw.  I have been tinkering with trials of back-and-forth with tabs etcetera - but the website has a strong inclination towards deleting whatever has been typed in the comments box.  (Previously I had naively assumed that the entries inside the comments box were the criterion for "activity".  But your advices make me come to the realization that it would of course be difficult for "offsite" text work within the box to register at SkS site.) 

    Simplest overall: I hope that the Administrator could add 60 minutes or so to the qualifying time recognized by the server.  Would there be some security concern in using a longer time?  Or is it a congestion problem, or something else?

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    Moderator Response:

    [BL] Pretty much the only thing I know about the code development is that it is a volunteer process. We'll look at it, but no promises.

    You need to stick to one comment box, in one tab. But that session is linked to timing of other sessions (as far as I can tell), so as long as you are clicking on links or refreshing a different page, your login is active.

    A web site is not an interactive ongoing dialog between server and browser. It's "you ask, I send, I don't know you any more, so next time you ask I have no idea you were here before". Cookies were invented to get around that limitation: "Oh, I gave you a cookie. Now I remember who you are". Much else in terms of modern web page design works around some of that, but in the case of the comments box here, it is still just "you are typing on your computer, and I (the server) know nothing until you click 'submit'".


  10. Hal Kantrud @ 8:

    As Eclectic points out, you need to define your time scales fully.

    Several Skeptical Science posts cover CO2 changes over different time scales:

    The last century or so

    The past 800,00 years

    The last 100 million years (or so)

    Hundreds of millions of years ago


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  11. I certainly did not mean to minimize the contribution of fossil fuel emissions toward the developing climate problem.  It is not an area I spend much time in, anymore, because the science is pretty well "evidenced". But, Industrial Animal Agriculture is flying under the radar and very little dialog exists on the plight of phytoplankton in the ocean, such essential creatures now suffering from ocean acidification.  Dialog, on this site, would contribute much to the big picture. 

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  12. I'm pretty sure our moderator tires of the task of referring participants to other threads.  SkepSci has been around a long time, and lots of participants have contributed much to its informations stores.  Hal Kantrud seems to be at a bit of a disadvantage since he is possibly fairly new to Skep/Sci and has not been through the voluminous scientific data regarding the topic of C02 emissions and the particular isotopic types of CO2 which lead us back to the origins of these different carbon dioxide "culprits".  Perhaps new contributors could receive an occasional reference from Skep/Sci on where to browse the "catalog" of threads, etc that permits new participants to get "on board". (??)

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    Moderator Response:

    [BL] Let's leave moderation to the moderators - the comments policy does consider moderation issues to be generally off-topic.

    All users are encouraged to use the "Search" function to find suitable threads and information, and the Most Used Climate Myths list is prominent near the top of the left margin.

  13. Hal Kantrud.  This topic of re-carbonizing of the soil is burdened with a wide variety of proposed remedies.  I recommend the Australian soil scientist, Dr. Christine Jones, as a good first source on the subject of carbon and soil. Also, I recommend a close look at the role of plankton, specifically phytoplankton, rather than new grasslands planted in degraded soils, as the way to, effectively, support the natural carbon cycle.  It appears that the human race may not have enough time to re-forest our de-forested lands and, in any case, re-forestation or re-grassing will run into property and legal rights issues which, in places like Brazil, will likely be insurmountable.

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  14. There is a study, currently in peer review, that approaches some elements of analysis differently than has been published over the last decade or two. This particular one asks the question, "what would we not have if we did not practice industrial animal agriculture?" The total absence of domesticated animals tended as food would see the reduction in methane and CO2 from animal respiration. The philosophical argument is: animal agriculture is a purely human invention, so the CO2 exhaled by livestock is no less unnatural than the CO2 emitted by cars and factories, etc.

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  15. To go on...the authors, Bar-On et al (2018), found that the biomass of humans and livestock combined have increased the total mammalian biomass by a factor of 4...It's not too much of a leap in logic to conclude that, above some minimum livestock population threshold or meat animal product consumption level, additional livestock units need be considered as added sources of GHG emissions akin to any other emissions-producing industrial factor of production.

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  16. Swampfox @14 and 15. The suggestion that industrial agriculture is articially manufacturing greenhouses gases has merit. Bear in mind you could argue that the explosion in human population is doing the same. And it its true that we have more humans than previously and perhaps more grazing animals and all expiring greenhouse gases. The issue with all these things is the respiration of both humans and animals is ultimately absorbed by natural carbon sinks through photosynthesis and this is regardless of how animals are farmed. Its a carbon neutral process. So the previous points are moot. Its quite a different thing from buring fossil fuels where emissions are not quickly absorbed by natural sinks.

    The increase in emissions from agriculture relates to transport and processing. For THAT particular reason there is merit in low meat diets, and more natural lower technology forms of farming like regenerative agriculture.

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  17. swampfoxh and Hal

    The additional carbon stored in (human and domestic animal) biomass is part of the modern carbon cyle. It would otherwise exist in another biosphere carbon compartment, such as soil or standing biomass, such as forests.

    It is true, however, that a significant amount of soil and aboveground standing carbon was, and is, on average, transferred to the atmosphere for thousands of years. Yes, it was at times a function of population due to agriculture expansion. Scientists summarize it under the term "land use change" (LUC), and you can read up on that in IPCC reports that discuss the carbon cyle and/or sources of atmospheric CO2 over time. A sumary graph is here:

    Figure TS.4

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  18. Hal @8, I think you may be looking for where the GHGs came from before the Industrial Revolution. The GH effect is necessary for life on Earth. Our black body temperature would be 34 deg C lower than the current avg T---too cold for liquid water, hence no life. Carbon is emitted by volcanos, which currently produce about 1-2% of our emissions annually, and converted to limestone by weathering of silica based rocks. You are correct that paleo-agriculture increased CO2. From around 5000 years ago to around 1790, our ancestors increased CO2 back up to where it was at the last climate optimum (280 ppm). Since then, the rise to 420 ppm has been mostly from the burning of fossil fuels.

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  19. I think it has been shown that industrial animal agriculture, which is about a 33% contributor to CO2e emissions, still carries the burden of deleterious ecological effects outside of the subject of GGEs, and, of course, the emissions footprint of nearly 8 billion humans added to the biomass is a major issue. Trying to add up all CO2e emissions while passing up the Industrial Animal Ag piece seems to leave a rather large deficiency in the math. Moreover, the body count of Humans and domestic animals, together, requires action, but COP26 avoided conversations that implicated both. The Animal Ag piece probably upsets environmental health because of its contribution to the list of nine serious adverse effects, starting with deforestation, desertification, fresh water use and land use changes made for the benefit of Animal Ag...the other 5 topics being no less important to curtail.

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