The impact of 4C of global warming

On a number of occasions I’ve highlighted Kevin Anderson saying

At 4oC most of the scientists I talk to about this, and the social scientists as well, would say it’s incompatible with organised global community.

I don’t know if this is what most scientists, and social scientists, would say, but there is a recent Guardian article that does discuss what would happen if we did warm by something close to 4oC. It does include a scientist who thinks it’s beyond our adaptation capabilities and who says [i]t’s difficult to see how we could accommodate a billion people or even half of that.

However, what I wanted to discuss is an alternative view. Ken Caldeira is quoted as saying

I don’t think that humans as a species or even industrial civilisation is seriously threatened.

His argument seems to be that we already have the technology to deal with the kind of climates we’re likely to experience.

However, there is a very large caveat, and this is where I have a pretty major issue. To successfully adapt to a world that has warmed by 4oC would require

cooperating as never before to radically reorganise our world: decoupling the political map from geography. However unrealistic it sounds, we’d need to look at the world afresh and see it in terms of where the resources are and then plan the population, food and energy production around that.

I just don’t believe we would do this. I can believe that those who have the resources might be able to adapt to a world that has warmed by 4oC. However, I’m not convinced that we would be willing to make the investments, and sacrifices, that would allow the billions who do not have these resources to do so. As Ken Caldeira points out richer people risk a loss to their quality of life, the poorer risk their actual lives.

What’s more, is that those who will may have the resources to adapt to a 4oC world will pre-dominantly be those who’ve contributed most to climate change, while those who will suffer most will probably be those who’ve contributed least. I find this possibility morally repugnant and, in my view, is something we really should be doing our best to avoid.

When I started writing this post, I was intending it to mostly be a prelude to an open thread. I would like to better understand the likely impact of 4oC of warming, so would be interested in what others have to say. As usual I’ve ended up writing more than I intended. To end on a positive note, I do think we’ll get our act together in time to give us a reasonable chance of avoiding ~4oC of warming. If we don’t, I’m not convinced that we’d be willing to really do enough to avoid an awful lot of suffering. I really hope I’m either right about us doing enough to avoid ~4oC of warming, or wrong about what we’d be willing to do if we don’t.

Video of Kevin Anderson’s seminar.
The heat is on over the climate crisis. Only radical measures will work (Guardian article by Gaia Vince).
Twitter thread by Andrew Dessler about what we mean when we ask “will we survive climate change?”

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65 Responses to The impact of 4C of global warming

  1. “We have already observed impacts of climate change on agriculture. We have assessed the amount of climate change we can adapt to. There’s a lot we can’t adapt to even at 2C. At 4C the impacts are very high and we cannot adapt to them.”
    Rachel Warren, University of East Anglia

    “ a 2°C world might be insurable, a 4°C world certainly would not be.”
    Henri de Castries, Chairman and CEO of AXA

    “There is a growing sense of panic in those who really understand what a 4°C world might be like”- Prof. Will Steffan, Director of the Australian National University Climate Change Institute.

    “Thinking through the implications of 4 degrees of warming shows that the impacts are so significant that the only real adaptation strategy is to avoid that at all cost because of the pain and suffering that is going to cost.” – Prof. Neil Adger, University of Exeter.

    “…there is also no certainty that adaptation to a 4°C world is possible. A 4°C world is likely to be one in which communities, cities and countries would experience severe disruptions, damage, and dislocation, with many of these risks spread unequally. It is likely that the poor will suffer most and the global community could become more fractured, and unequal than today. The projected 4°C warming simply must not be allowed to occur” – World Bank report (2012) “Turn down the heat: why a 4°C warmer world must be avoided”

  2. I respect Ken Caldeira, but I would pose this question. If we are envisaging an adaptation scenario that requires “cooperating as never before to radically reorganise our world”, why not channel that cooperation to urgently decarbonise (mitigation scenarios)? We have the technology to do this. In fact, we can even bet on a few horses to hedge our bets. Yes, it is not trivial building out renewables, chemical storage networks, etc. in a tight window – but its doable. We just need political leadership, and get on and do it. The recent Net Zero report by the Committee on Climate Change is worth a study, as it provides a strategy for getting to zero by 2050 (maybe not as fast as many want, but a huge step forward if adopted by UK Govt). Planning to get to ‘well below 2C’ is worth fighting for. Adapting to well above 2C is a very poor alternative, with inumerable uncertainties and surprises awaiting us.

  3. John Hartz says:

    We are already seeing a paradigm shift in in the governance of Western countries from democracies to oligarchies. The two primary causes of this shift are the almost unlimited power of multinational corporations and the fear of other. The rise of ultra conservative governance in Europe was precipitated by the influx of refugees from the Middle East. The rise of ultra conservative governance in the US was precipitated by the influx of refugees from Mexico and Central America. If you think those refugee streams were significant hold on to your seat belt a climate chaos spins out of control. Populations on the both sides of man-made borders will be decimated by warfare — too little inhabitable territory for too many people.

    When contemplating what conditions mare be like in the biosphere under a 4C global warning scenario, let’s not lose sight of the fact that the human race is also destroying many components of the biosphere through the proliferation of plastics. jAnd then there’s ocean acidification to ta take into account.

    “We have met the enemy and they is us.” – Pogo

  4. dikranmarsupial says:

    I think Prof. Caldera is right the we are probably technically and economically capable of dealing with 4C of warming, but I agree that we also need to be politically capable for that to matter. Rem acu tetigisti. I am not sanguine about that at all.

  5. Richard,

    If we are envisaging an adaptation scenario that requires “cooperating as never before to radically reorganise our world”, why not channel that cooperation to urgently decarbonise (mitigation scenarios)?

    Yes, it would seem more sensible to do radical things to decarbonise, rather than having to do radical things to deal with the consequences of not having done so. However, my sense is that Ken Caldeira was answering the question as to whether or not we could potentially deal successfully with 4C of warming. I didn’t get the sense that he was suggesting that doing so would be optimal.

  6. izen says:


    While I have little confidence in the capability of our present systems of governence being able to act to avoid 4C of warming if such a change is geo-physically possible, and –

    “decoupling the political map from geography. However unrealistic it sounds, we’d need to look at the world afresh and see it in terms of where the resources are and then plan the population, food and energy production around that.”

    I would agree is not something ‘we’ are capable of doing as a result of rational planning, I want to put forward a slightly more positive view than the Cassandra-like view of total civilisational collapse.

    First, over the last century and a bit human society has managed, without explicit planning or policy’ to transition from around 1 billion in abject poverty to ~8 billion of which most enjoy(?) a quality of life in terms of access to food, clean water, waste disposal, education and health care that significantly exceeds the state in which the past 1 billion lived.
    Although there are still around 1 billion living in that condition.

    I dont see the future changes that will be required to avoid catastrophe as something imposed by wise and benign central planning and policy.
    But as something that will be driven by mass migration, forced adaption and ad hoc partial solutions to emergent problems, including an inevitable level of morally repugnant death and suffering by a significant proportion of the least culpable of the 8 billion.

    The largest threat is to disruption of agriculture and food supply. But the ability to adapt to the recent population rise, even if it has involved exploiting fossil fuels to expand our food growing efficiency and distribution does at least indicate that such resilience in the face of major change is possible. Most of that adaption was not the result of careful comprehensive policy design but evolved from necessity.

    I am not suggesting that the cornucopians of the BTI are right, I think I grasp the difference between AM/FM.
    But history indicates, contrary to the conservative view taken by each generation, that our social and political structure DOES change radically. Not by planned intention, but as a forced evolution in response to contingent circumstances.
    Asimov’s foundation and empire comes to mind…

    I am not suggesting that no individual involvement or commitment is required, that we can sit back and let it happen by the wave of some inevitable ‘invisible hand’. societal change is driven by each individual adopting a new attitude, or metaphor that shapes how they understand and shape their own lives. There are inevitable dangers that we can guard against. When large social changes occur that threaten the status quo, one common effect is a rise in regressive political approaches to defend and oppose the changes. The rise in political ‘populism’ is very much a symptom of the incipient radical changes, a polarisation attempting to stop them. It may be as impotent as Canute to stem the rising tide of change, but it can still drown a lot of people before it bows to the unavoidable.

    Radical change has become inevitable.
    In the unlikely event rational global action is taken to avoid 4C, it will require changes almost as large as occurred between 1860 and 1960.
    In the more likely event climate change is largely unmanaged, the adaption that happens will also involve radical change. It wont be pretty, and for a lot of the population it wont be easy or comfortable. But I would concur with Ken Caldeira, with support from the history of change in human society, that adaptive change is the more likely response than total collapse and a return to a billion of less hunter-gatherers and subsistence farmers and nomadic pastoralists.

    As in the 1860s there is just too large a shift to large scale urban living, and potential technology waiting in the wings, to make it likely, never mind inevitable, that human society would or could return to a early iron-age feudal and parochial tribalism.

    We may be down in the gutter, but we look up at the Stars!

  7. talies says:

    Maybe food production can become largely independent of climate. Wind powered artificial lights inside solid buildings. And other adaptations for storms and heatwaves.

    But my sinking feeling is that these would be the preserve of rich countries – perhaps only the rich of those countries.

    And most of the world would be suffering in ways that the enlightened of the rich would not want to think about. Climate migrants turned away in their billions.

    But alternatively this food production might be so cheap it would be available to everyone.
    The possibilities would probably be subject to chaotic alternatives if you tried to model them
    eg Conflict and turmoil, technology driven, could prevent any adaptive solutions being implemented.
    When I was 12, in the 1950s, I was given a Readers’ Digest atlas of the world showing population estimates of 6 billion by the end of the century. Then in my teens I came to the conclusion that the exponential growth could not possibly continue that long. Something would stop it, preferably something planned, and not disastrous. Turned out I was completely wrong. But that did not cause me to stop my life long campaign for the environment, and then climate in particular.

    The feeling that it would all catch up with us continued. I sometimes think our industrial society is like a freak wave, drawing power from the past (Victorian exploitation) and from the future.

  8. jacksmith4tx says:

    I did read about the Net Zero report over on Carbon Brief but I feel it side steps the underlying issues of consumption and environmental degradation. I still hold Project Drawdown as the most comprehensive set of policies that have a chance of avoiding the worst outcomes.
    The single biggest obstacle to tackling a global existential threat like climate change might just be the nearly 250 trillion of global debt growing at a compound rate > 5%.
    After the global economic system resets perhaps long term problems like climate change will receive a higher priority. Sadly I’m not expecting consumption patterns to moderate enough to change our current trajectory before 2050. Of course there is always Plan B; geoengineering.

  9. notabilia says:

    All the climate scientists, including Kevin Anderson, are rank amateurs when it comes to political science. They seem to will themselves into thinking there is some sort of global governance structure that can implement their plans and schemes when there is only a supersystem governed according to corporate transnational carbon dioxide imperatives.

    The result is anti-politics run by absolute idiots and malingering extractivists. There is not a piece of evidence tied to our social reality that suggests the slightest ability or inroad or regulatory opportunity to cease the chase after cheap energy.

  10. russellseitz says:

    Beware of the claque with just one playbook.

    John Hartz may warn of ” a paradigm shift in in the governance of Western countries from democracies to oligarchies. ” but what about the self-appointed consortium that gathered at the Columbia School of Jopurnalism last month to declare itself the arbiter of climate policy by offering a unified climate communication playbook.

    The depressing self-similarity of the wave of quotations flowing from that event should serve to remind us that climate discourse is too important to be left to a narrow wedge of political opinion. Those who subscribe to The Nation and The Guardian are no more immune to echo chamber effcts than thos who limit their journalistic input to Fox and the Murdoch papers.

  11. talies says:

    JackSmith, isn’t the global debt a sort of imaginary money everyone owes to each other? (I’m no economist)

  12. Joshua says:

    JH –

    The rise of ultra conservative governance in the US was precipitated by the influx of refugees from Mexico and Central America.

    Just to nitpick, FWIW that may be the perception, but perhaps the reality is a bit stickier.

    The number of unauthorized immigrants living in the United States was lower in 2016 than at any time since 2004. This decline is due mainly to a large drop in the number of new unauthorized immigrants, especially Mexicans, coming into the country.

  13. jacksmith4tx says:

    talies; yes it’s entirely a human conjecture without any physical attributes (like science).

  14. Greg Robie says:

    Given the natural feedbacks that come with a global 4°C of warming, isn’t it hubris/motivated reasoning to feel there could be a stable climate anywhere in our future?

    sNAILmALEnotHAIL …but pace’n myself

    life is for learning so all my failures must mean that I’m wicked smart


  15. Griff. says:

    Is the world at 4 C one any of us would want to live in ?

    Oceans no longer a viable protein source due to ecological collapse.
    Large areas of the oceans dead zones outgassing hydrogen sulfide lethal for surface life down wind. Tropical continental regions suffering from periodic heat waves deadly to mammalian life .
    Droughts far longer and deeper than any historical events known interspersed with extremes of participation. Storms of intensity’s never before recorded. Major ecological collapse in the regions still available for civilization. 50% of all species extinct most of the rest rapidly heading that way.

    Ken Caldeira’s views and anyone else who thinks.
    “People live in Houston, Miami and Atlanta because they live in air conditioning through the hot summers.they can watch whatever is the successor to Game of Thrones on TV, as the natural world decays around them,””
    It is the Ecology stupid ! Humanity’s future is inevitably linked to the health of Gaia.

    Homo sapiens is an ape that still reacts to threats with flight or fight. Our animal nature will spread the impacts far outside of badly effected regions. Use of nuclear weapons by destabilized country’s and a rise of self interested strong arm regimes. Resource wars rampant. Collapse of organized global trade making high tech solutions unavailable to most. Billions of displaced seeking sanctuary. Retreat from coastal inundation and the costs of the armed life boat boarder protection requiring a large percentage of any remaining economic activity.

    Civilization remotely as we know it remaining at 4C is deluded thinking. Even for the presently rich. .

    As to the likelihood of my fearmongering rant.
    Humanity has been grappling with this problem for the last 30 years. The keeling curve is still rising faster than ever . We are now seeing a record 10 ppm rise every four years. We have failed to curb emissions growth let alone move towards the carbon neutral world we need to see in a few short decades.
    It may not be under our control far sooner than we would like to think.
    Trajectories of the Earth System in the Anthropocene

    As a non scientist I see the reticence of the science community to step outside of the bounds of scientific certainty and address the possibility of an existential threat to human civilization In the long tail of risk a failure to lead from a position of knowledge .
    Refusing to honestly address the real risks we face is only making the worse possible outcomes more likely.

    ‘by all the operation of the orbs/ From whom we do exist and cease to be’. It’s the threat of ceasing to be that worries people now.
    Some bloke called Will.

  16. notabilia,

    They seem to will themselves into thinking there is some sort of global governance structure that can implement their plans and schemes

    What makes you think this? As far as I can see, those you name are quite realistic about the difficulty in trying to implement what would be needed to avoid warming by something like 4oC.

  17. russellseitz says:

    Griff. says: May 21, 2019 at 2:34 am
    Is the world at 4 C one any of us would want to live in ?

    You should ask that of those presently living 5 drgrees closer to the equator than you do,
    for the quality of their lives may be the answer to your question

  18. John Randall says:

    Here’s another perspective. The minimum average global surface temperature in the most recent ice age was 11C. Today it is 4 C higher. Think of how radically the planet changed over that 4 C transition to bring us to a livable planet. The next 4 C will be more radical because it will happen much faster and the planet will altered radically away from livability.

  19. John,
    Yes, that’s been my perspective. If a 4C change in global surface temperature is the difference between a glacial, and an inter-glacial, then a 4C change suggests a substantial change in climate. Add to that that we’re doing this much faster than the change between a glacial and an inter-glacial and it’s hard to see how the impact won’t be substantial.

  20. David B. Benson says:

    Not to mention the at least 40 meter sea level rise.

  21. Chubbs says:

    Without the capability to model change in ice sheet/biomes/permafrost/oceans/regional climate/ etc., I don’t think we have a good handle on what a 4C world would be like. Technical, economic and political capability in the future are also uncertain. Rapid change – yes, winners and losers — yes, “cooperating as never before” – unlikely.

  22. David B. Benson says:

    Chubbs, it is only necessary to look to the distant past, when it was so warm; the Miocene.

  23. Ben McMillan says:

    Like the Miocene… maybe. Except everything changes 1000x faster and most things don’t have time to move or adapt.

  24. Whenever I see a discussion about a 4C world, I think I see a hidden assumption that we would have some control about getting the earth system to stabilize at roughly a particular temperature level.

    As I understand it, the planet seems to shift between certain climate/temperature regimes, and there are intermediate temperature points along those shifts that are inherently unstable. Feedbacks (and cascading tipping elements) kick in such that the system either (eventually) retreats to an earlier equilibrium, or force it to an even higher stabilization point.

    And I am not talking about “runaway”, just the observation that, say, during the Quaternary, we saw two roughly stable temperature regimes, and a whole bunch in between that were highly unstable, brief waystations to an apparent attractor state.

    And I am not sure, but I don’t think there is a paleo analogue that was stable in the ~4C range. Which should at least give us pause about confidently discussing about how we would adapt to 4C…

    (although more a survey/conjecture, this PNAS paper last year discusses this in more detail

  25. Jackie (Smith), I agree that Drawdown offers many great ways of addressing the need to get to zero; many are quite ‘low tech’, whereas others are high tech. The CCC Net Zero report – from a statutiry body – is to some extent constrained by its terms of reference so could not really get into too much social reegineering aspects or even reduced consumption; but these can be additive to its recommendations. Increased efficiency, renewables, and energy storage can take us a long way.

    I was talking to 12yr olds today on ‘Energy: Past, Present and Future’ and explored 6 themes for decarbonization:
    – Doing less of some things (more staycations, less flying);
    – Doing things differently (train to Bordeaux rather than flying);
    – Waste less (in food, building construction, etc.);
    – Renewables + energy storage build out (coupled to hydrogen economy);
    – Efficiency (light bulbs, buildings, etc); and finally,
    – Change how we do things.

    This last one is in many ways the most important: It is not simply, for example, replacing a petrol car with an EV, but asking ‘do I really need a car?’. Here I asked them to think laterally about topics, such as
    – Sharing economy
    – Circular economy
    – Smart grids and storag
    – Electrification of transport
    – Low waste living (less consumption)
    – Community Energy
    – Autonomous vehicles
    – Smart Cities
    – Hyrdrogen economy.
    – etc (only limited by our imagination)

    To often we do the maths based on replacing existing power systems to do existing ways of living and working.

    We need – as Greta Says – to use Cathedral Thinking. We have all the building blocks invented. We need to push on with the foundations, even while we do not have all the answers on how we will live and work in the future.

    These kids were wonderful and I was so impressed with them. I feel really great to know that there are 12 year olds in British schools that, frankly, could run rings around many of my generation (I am a grandfather).

  26. JCH says:

    A lot of people lived in Houston, Dallas, and Atlanta before air conditioning. My millionaire Aunt lived in hot-as-heck Dallas from 1962 until 2008 with no air conditioning. She didn’t even have an attic fan.

  27. I’ve not seen the impact of climate change put quite this way before…
    Prof. Rob Jackson: “It’ll take a thousand years of people—30 generations of people—to pay the price of what we’re doing today.”*

    Of course I guess economists and politicians would argue that it’s irrelevant to factor in the impact on generations over the next millennia.


  28. jacksmith4tx says:

    Richard, (Jack=dude)
    It might surprise some people that Project Drawdown was adopted by the Commonwealth back in 2017 but I haven’t seen much in the way of tangible results yet.

    But what about the deeper problems of how we are chemically altering the air, water and soil?
    It seems obvious to me we are going to resort to geoengineering and genetic engineering because it will be the fastest, cheapest ‘fix’.

    This book, “The Planet Remade: How Geoengineering Could Change the World” by Oliver Morton is a good look at the possibilities.
    “The risks of global warming are pressing and potentially vast. The difficulty of doing without fossil fuels is daunting, possibly even insurmountable. So there is an urgent need to rethink our responses to the crisis. To meet that need, a small but increasingly influential group of scientists is exploring proposals for planned human intervention in the climate system: a stratospheric veil against the sun, the cultivation of photosynthetic plankton, fleets of unmanned ships seeding the clouds. These are the technologies of geoengineerin–and as Oliver Morton argues in this visionary book, it would be as irresponsible to ignore them as it would be foolish to see them as a simple solution to the problem.
    “The Planet Remade” explores the history, politics, and cutting-edge science of geoengineering. Morton weighs both the promise and perils of these controversial strategies and puts them in the broadest possible context. The past century’s changes to the planet–to the clouds and the soils, to the winds and the seas, to the great cycles of nitrogen and carbon–have been far more profound than most of us realize. Appreciating those changes clarifies not just the scale of what needs to be done about global warming, but also our relationship to nature.
    Climate change is not just one of the twenty-first century’s defining political challenges. Morton untangles the implications of our failure to meet the challenge of climate change and reintroduces the hope that we might. He addresses the deep fear that comes with seeing humans as a force of nature, and asks what it might mean–and what it might require of us–to try and use that force for good.”

  29. If we assume that most of the warming will occur at high latitudes (and accept the dramatic effect that will have on the weather), the rest of the world will likely not collapse. Crop decisions will change–again. Housing requirements will change–again. Shorelines will change–again.

    It will all happen too quickly and that will be very disruptive. It will be difficult for all and dangerous for some. It will not be pretty and it will be expensive. But to say it will cause the collapse of civilizations is close to absurd.

    As I mentioned in another thread, I have lived comfortably in places that are more than 4C above the current GAT of 15.7C. They grew crops there. They maintained a high level of civilization. They cared for the poor and the elderly.

    We can too.

  30. Tom,

    But to say it will cause the collapse of civilizations is close to absurd.

    You’re always remarkably confident about these kind of things.

    We can too.

    But will we?

  31. The Very Reverend Jebediah Hypotenuse says:

    russellseitz says:

    ‘Is the world at 4 C one any of us would want to live in ?’
    You should ask that of those presently living 5 drgrees closer to the equator than you do,
    for the quality of their lives may be the answer to your question

    This argument explains why Canadians and Swedes are so poor, and Puerto Rico, Bangladesh, and Eritrea are this year’s ‘go-to’ luxury destinations.

    thomaswfuller2 says:

    I have lived comfortably in places that are more than 4C above the current GAT of 15.7C.
    They grew crops there.

    This argument explains why we should aim for at least 4 C of warming.
    And the quicker we get there, the better.

    At 2 C, most coastal cities will become dysfunctional water-parks, coral reef ecosystems will finish going extinct, farming will be a worse gamble than the slot machine, and today’s refugee ‘crisis’ will seem like a quaint fairy-tale.

    I’m glad the internet is forever.
    Comments like the above deserve to out-live us.

  32. Jack dude! … I am a big un-=fan of geoengineering! Once again the poorest get shafted … no power to inflence, greatest vulnerability to unintended side effects. It is amazing how the biggest deniers of man made global warming will often love big geoengineering ‘solutions’ (dystopian complex?). That is, do nothing to mitigate then spend a fortune reenacting a James Bond movie. Maybe it is a kind of top down / big power / centralised solution bias (which is rather in contradiction to the whole ‘we hate big Government’ declared philosophy). Odd then that maybe the solutions – such as in Drawdown – are often bottom up and not requiring ‘global big state’ (paranoia) [those conspiracy theorists really ought to take a 101 in basic philosophy, to help get their story straight]. I am actually optimistic we can do transformational social reorganizational solutions above and beyond the (obvious) decarbonization that will accelerate net zero.

  33. russellseitz says:

    RE:” do nothing to mitigate then spend a fortune reenacting a James Bond movie”

    One sees that the most expensive James Bond film to date, appropriately named “Skyfall” cost $300,000,000 to produce, an order of magnitude more than Andrew Parker’s reported 2013 estimate of total expenditure on geoengineering research through the time of its release.

  34. Research is fine. Deployment is another matter.

  35. russellseitz says:

    “This argument explains why Canadians and Swedes are so poor, and Puerto Rico, Bangladesh, and Eritrea are this year’s ‘go-to’ luxury destinations.”

    Don’t be a square, Hypoteneuse.

    Coasts from the Caribbean to the Bay of Bengal and the Erithrean Sea are awash in Canadian and Swedish snowbirds of modest means every winter. Hyperthermia is no joke, but neither is Hype.

  36. Steven Mosher says:

    ok, what about 3.9C?

  37. sheldonjwalker says:

    It is relatively easy to get an approximate idea of what the world will be like, with 4 C of global warming.

    1) Pick a country (country A).

    2) Look up the average temperature of country A on this webpage (the table is at the bottom of the webpage).

    3) Add 4 to the average temperature of country A, to get the new temperature.

    4) Now find another country (country B) in the table, that has an average temperature approximately equal to the new temperature.

    5) When the temperature of country A reaches the new temperature, country A’s new climate will be similar to the climate of country B now.


    country A = United States of America
    average temperature of United States of America = 12.1 degrees Celsius

    new temperature = 12.1 + 4.0 = 16.1 degrees Celsius

    find country B in the table, which has an average temperature of about 16.1 degrees Celsius

    Spain has an average temperature of 15.9 degrees Celsius

    Conclusion: With 4 C of global warming, United States of America with have a climate similar to Spain now.

    Repeat these steps for as many countries as you like.

  38. Joshua says:

    Conclusion: With 4 C of global warming, United States of America with have a climate similar to Spain now.

    Sheldon makes a great point. Countries that undergo dramatic change to reach average temperature X will be exactly like other counties that had an average of temperature X for hundreds of years.

    No difference.

    If only climate scientists had Sheldon around with his statistics genius, they would have realized that.

  39. sheldonjwalker says:


    How fast are you planning on warming at?

    We are currently warming at about 0.02 degrees Celsius per year.

    Your whole life could go by, without seeing much change.

    Remember, seasonal warming is 2,500 times faster than global warming (about 25.0 degC in 6 months, compared to about 0.01 degC in 6 months).

    You need to relax.

  40. Joshua says:

    Sheldon. Your point was vapid, yet you presented it as if it were somehow profound. It ignores obvious and relevant considerations. As does your point about seasonal warming.

    Why do you bother with such trivial nonsense?

  41. sheldonjwalker says:

    My method is better than anything that other people have suggested.

    It is simple, and practical. It doesn’t depend on any risky assumptions.

    My method takes things like latitude, elevation, proximity to ocean, etc, into account. Because these factors determine the current temperature.

    As a first approximation, I don’t think that YOU can do any better. Why do you need to make everything complicated. Simplicity is a virtue.

    My method is NOT trivial. And it is NOT nonsense. Provide some evidence to support your vacuous claim.

  42. Joshua says:

    Sheldon –

    I think it is quite-evident why the arguments you presented are trivial and vapid.

    But if you think they’re profound, that’s just fine with me. Anyway, have a nice night.

  43. sheldonjwalker says:


    You are claiming that it is obvious why the arguments that I presented are trivial and vapid.

    It is not obvious to me.

    Why won’t you tell me the reasons why my arguments are trivial and vapid.

    Are you going to keep the reasons a secret?

    Are scientists allowed to write papers, where they say what the answer is, but don’t present any evidence or proof? They just claim that the answer is obvious.

    I can prove that you are wrong. But I am not going to tell you why you are wrong. It is too obvious.

  44. b fagan says:

    I think that Sheldon and maybe some other people forget that each degree of global temperature rise increases relatively little heat gain over lots of ocean, combined with much more heat gain over less land area. In USA we also have the conversion issue, so “two degrees” sounds smaller already to the locals.

    So breaking out the “global” rate might be interesting – especially to look at the areas where most people live, then look at the continents that have the most people still living off of what they can grow or raise on land they use – remember Syria’s revolution was kicked by a drought forcing a large flux of small-plot farmers into cities where aid was not forthcoming. And that was far below 4°C global warming.

    Decadal rate of warming between 1969 and now (NOAA Climate at a Glance)
    +0.17°C – global land and ocean
    +0.13°C – global ocean
    +0.28°C – global land
    +0.31°C – NH land
    +0.24°C – Africa
    +0.34°C – Asia

    Land globally warmed at twice the rate of the overall rate. Asia’s warming faster. I’m not confident this will turn into humanity’s finest hour – I think we’ll muddle along as we usually do, but as impacts accumulate I start wondering things like how Chinese Siberia will be 80 years from now, and how did it get that way?

    The other concern is resilience for bad crop years – farmers in the US Midwest lost stored grain this year from floods, this after a wet fall prevented adding nitrogen to the fields, and now late planting – if they can plant. How much more farming will California support if the Colorado sharing falls apart? What happens if the aggressive leasing of African cropland by China and others bumps into failing crops for locals? Russia’s crop loss in 2010’s massive heatwave was a factor in food price increases everywhere, which factored into causing the Arab Spring. The Indian monsoons might be wetter for a while but what happens if the rains, and snowfall into the rivers shared by India, Pakistan, China, Bangladesh, Vietnam, etc. go into decline? India’s already over-pumping ground water.

    So suppose two years of bad breaks globally on crops, then a random nation or one of the 0.01% decides to pump some cooling SO2 in the atmosphere, and overshoots – or nature decides to help. My big fear of that type of geoengineering is precisely that once started it would likely be continued, and Pinatubo didn’t schedule its last appointment with us.

    I’m generally the cautious optimist type, but it’s hard to see projected population numbers do well if a 4°C global rise transpires within the next 80 years. There’d still be people, but who knows how many, and hard to see that produce a peaceful, healthy transition to an industrialized, sustaining population that declines by just reduced birthrates. The tools we have we’re having trouble implementing at speed, the possible tools like geoengineering would be powerful tools used by unskilled amateurs. If the increase is spread over 180 years? Much more likely we could muddle through.

  45. izen says:

    “Why won’t you tell me the reasons why my arguments are trivial and vapid.”

    Trivial and vapid may be a little harsh.
    But your comparison between ~4C global warming and moving a little closer to the equator does reveal that you have been misled by the way AGW has been reported as a simple average rise in global temperature, just as climate sensitivity is quoted as a single metric.

    That average is NOT evenly distributed. Like sea level rise, the actual amount of warming will vary at a local level. Polar amplification is the most obvious example which is already seen.
    It also fails to address the significant change in the variability of the climate that the simple average obscures. Parts of the US will not just warm to be more like Spain, they will also gain many more extreme weather events. Increased drought, alternating with flash floods and if coastal, a new exposure to hurricanes and serve storms are implicit, but rarely mentioned in the ‘headline figure of the rising average.

    The unseasonal and extremely intense tropical storms hitting the Est coast of Africa and the Bay of Bengal are just a harbinger of what is to come. If your attention is myopically parochial the last year of extreme floods, hurricanes and firestorms in the US 48 should give you pause before making such crass comparisons between the significant changes in climate embedded in the average global figure for warming and such simplistic geographical shifts in position as a way of understanding the impacts.

  46. Willard says:

    > It is relatively easy to get an approximate idea of what the world will be like, with 4 C of global warming.

    Then follows Sheldon’s usual drive-by. Drive-by done. One per thread, otherwise it’s not a drive-by anymore.

    Andrew already responded to it, BTW:

  47. Ben McMillan says:

    We know how historical civilisations have been impacted when they faced abrupt climate change. Several of them just collapsed. Looks like it only took a few years of drought in 2000BC to take out a couple of them. Crop failure in more recent time has also lead to mass migration.

    +4C on average, but twice as much in many places, plus rain patterns changing, glaciers that allow irrigation disappearing, and a couple of meters of sea level rise, would have been enough to finish of a large fraction of former empires.

    Hoping that technology will save us this time seems like a risky strategy, and at best true only for the well-off.

    I think the thing that bugs me though, that even if human civilisation can miraculously avoid serious ill-effects, this is still a severe mass-extinction event.

  48. russellseitz says:


    We know how historical civilisations have been impacted when they faced abrupt climate change. Several of them just collapsed. ”

    Others fell asleep reading Jared Diamond.

  49. David B. Benson says:

    As I make it, similar to the Middle Miocene Climatic Optimum, as the stage is named. A noticeable feature was the 55 meter higher sea stand. That would eliminate alotta agriculture.

  50. Chubbs says:

    Yes like the Miocene, but with many vestiges of the Holocene, all earth systems out of equilibrium. Presumably also without fossil fuels, A great time to be a scientist or an engineer or a politician.

  51. In separate conversations, members of the blogosphere aligned with climate activism can and do have serious conversations. But when you’re all together in a thread such as this, it seems as if you’re competing for the title of gloomiest and doomiest.

    The IPCC, first of all, does not predict or project 4C as the most likely result of human induced warming. It admits it as a possibility. Secondly, their projections of impacts is far lighter than those offered up here in this thread and elsewhere.

    Do remember that climate scientists say that the great ice sheets in Greenland and Antarctica will require 3,000 or more years of monotonic warming to reduce their respective masses by as much as 50%.

    Reality is waiting patiently for your return.

  52. Ben McMillan says:

    Most of the flora/fauna would be in the wrong places and not adapted to the conditions.

    Might be a good time to be a logger and harvest some dead forest.

  53. Dave_Geologist says:

    sheldon, you’re forgetting Clausius-Clapeyron. 1.07^4 = 1.31. Other things being equal, 31% more evaporation and 31% more rainfall. So if you’re a dry country, you need to pick one 31% drier as well as 4°C warmer. If a wet country, one 31% wetter. If a seasonal country like Spain, one with a dry season 31% drier and a wet season 31% wetter. If you’re California, you also have to consider whether the water stored as snow in winter and delivered during the dry season will have run off into the sea during the wet season.

    If you want to see what a 4°C increase does to the hydrological cycle, go to Google Scholar and look for the PETM and the Carnian Pluvial Event (both were in hotter worlds, but the sudden, incremental temperature increase was about the same). The change in hydrological cycle during the PETM was so extreme we can actually see its signature in the clay mineralogy of all the world’s oceans.And how do you think the Carnian Pluvial Event got is name? It was so obvious geologists named it before they even knew it was also a warming event. Farmers won’t know what’s hit them. There will be food wars, land wars and water wars. I wouldn’t be surprised if a billion starve. I’m sure there will be survivors, and it won’t be quite as bad as Mad Max – a full PETM of about 8°C would bring us Mad Max – but it’s not something I’d want on my conscience.

    Coincidentally, the conference abstract I mentioned a few months ago on the unprecedented nature of the 2009 and 2015 Cumbria floods has now been published. Biggest for 558 years; 2009 flood estimated recurrence interval about 2,000 years; actual recurrence six years, so of course that 2,000 year recurrence interval is the old normal, not the new normal. It’s linked from this Guardian article: Floods in 2009 and 2015 were worst in Cumbria for centuries.

  54. Dave_Geologist says:

    The risk of getting to 4°C is not just what happens then, it’s what happens next. Do we trigger some tipping point as happened in the PETM, and in the subsequent, smaller ETM-2 (the PETM is ETM-1), but not in the succeeding, smaller ETMs? Are we playing Russian Roulette with five bullets or two bullets?

    There is still debate whether the PETM trigger was exogenous (a one-off burning of oil, coal or oil source rocks due to volcanic activity) or endogenous (a tipping point such as methane hydrate release or thawing of all the permafrost on the Antarctic Plateau all at once). Or a bit of both, endogenous amplification of exogenous. This paper (Reduced carbon cycle resilience across the Palaeocene–Eocene Thermal Maximum) finds that the carbon cycle got sick in the thousands of years before each event, but sick in a different way between the two. Something bad (for the lived environment of the time, about 4°C warmer than today) was already happening before the PETM exogenous event, if there was one. The fact that they were different might argue for an exogeneous PETM. However the fact that they got weaker has been argued as evidence for a legacy effect or carbon debt. IOW a large store of carbon had built up by the PETM, and so much was released that the inventory available for each subsequent event was smaller (Milankovitch cycles have been argued for pacing them, but the dating is a bit imprecise so far back).

    Oh, and an enhanced hydrological cycle can do more than change the clay content of deep-sea sediments. It can change places with seasonal rainfall into places with multi-decade droughts interrupted by megafloods. Abrupt increase in seasonal extreme precipitation at the Paleocene-Eocene boundary. Now who said scientists can’t write a catchy title? Good luck farming in that. And I wonder if that might erode/and or oxidise a bunch of stored terrestrial carbon? Is that even on our current list of tipping points? Looks like it should be. Palaeocene–Eocene Thermal Maximum prolonged by fossil carbon oxidation.

    This work provides evidence for an order of magnitude increase in fossil carbon delivery to the oceans that began ~10–20 kyr after the event onset and demonstrates that the oxidation of remobilized fossil carbon released between 10^2 and 10^4 PgC as CO2 during the body of the Palaeocene–Eocene Thermal Maximum. The estimated mass is sufficient to have sustained the elevated atmospheric CO2 levels required by the prolonged global carbon isotope excursion. Even after considering uncertainties in the sedimentation rates, these results indicate that the enhanced erosion, mobilization and oxidation of ancient sedimentary carbon contributed to the delayed recovery of the climate system for many thousands of years.

  55. Tom,

    The IPCC, first of all, does not predict or project 4C as the most likely result of human induced warming. It admits it as a possibility.

    Technically, this is true. However, given where we are now it seems like it will be extremely difficult to keep warming below 2C, and the current trajectory suggests something close to 3.5C. Given the uncertainties, it could be higher, or lower. However, 4C of warming is far from being unlikely.

    Secondly, their projections of impacts is far lighter than those offered up here in this thread and elsewhere.

    I don’t think this is correct, but I’m not that bothered if you don’t back it up.

  56. Chubbs says:

    We have 65M of sea level tied up in ice sheets. So Tom’s loss of 50% in 3000 years, gives roughly 1 meter of sea level rise every century. However losses wont be a linear, the most unstable portion, roughly 10-20 meters or so, will slide into the sea, not melt slowly like an ice cube.

  57. David B. Benson says:

    Chubbs, right idea but wrong numbers. The total cryosphere is equivalent to closer to 80 meters, but probably it wouldn’t all melt. But 60 m in 3000 years is 2 m per century.

    You are right in stating that the melt will be nonlinear.

  58. Ben McMillan says:

    A study suggesting Antarctica alone could lead to 15m sea level rise by 2500 (in an ~4C scenario):

    A few meters per century looks likely in total in a 4C scenario. The predicted ~1m rise by 2100 for high forcing scenarios is an accelerating curve, so the rate in 2100 is >1m/century.

    There is evidence that sea level rise can happen in several-meter bursts

  59. The Very Reverend Jebediah Hypotenuse says:

    [The IPCC] projections of impacts is far lighter than those offered up here in this thread and elsewhere.
    Reality is waiting patiently for your return.


    We find that a global total SLR exceeding 2 m by 2100 lies within the 90% uncertainty bounds for a high emission scenario. This is more than twice the upper value put forward by the Intergovernmental Panel on Climate Change in the Fifth Assessment Report.

  60. Norvergence says:

    Reblogged this on Norvergence and commented:
    Thanks for this post.

    We at Norvergence working in the same field and making people aware of global warming.

  61. Snape says:

    July, 2009, was a record breaker in Phoenix. Warmest since at least 1933. The monthly anomaly, however, was only +1.9C

    That’s an extreme example, but the same idea holds wherever you live. The hottest month in memory for your area was likely less than +4.0C above average.

    A lot of talk about SLR, but don’t forget about wildfires. With 4.0 C warming, summers out West would be awful:

  62. Snape says:

    For Sheldon

    “New York Wilts Under Record-Breaking Heat Wave”

    “With the temperature reaching 103 degrees in Central Park at 3:11 p.m., breaking the former record high of 101 degrees for the day set in 1999, Con Edison officials braced for the greatest demand for power they had ever had to supply. The long red arrow on the dial projected on a screen in the utility company’s command center in Manhattan hovered at the threshold of uncharted territory — 13,141 megawatts consumed at one time — for most of the afternoon”

    The summer of 2010 was the record warmest in New York’s Central Park – going back 125 years. Only +1.6C above average!!

    Imagine if +4.0C was the new normal.

  63. Snape says:


    “It’s Like Hell Here”

    And what was the monthly anomaly for Australia in January, 2019? +2.91C
    Again, imagine if +4.0C was the norm.

  64. Jeffh says:

    I have been away in Canada and thus I am late responding to this thread. Let me make one thing clear, speaking as a population ecologist. It is utter insanity to speak about the prospects of human survival if the surface temperature of the Earth rises 4 degrees over the coming 5-10 decades. Caldeira, like others proposing this piffle, need to stay in their lane. If the temperature rises this rapidly in this blink of a geological eye, then we, along with 80% or more of the planet’s species are finished. When the great dying occurred at the Permian-Triassic interface, vanquishing between 75% and 90% of biodiversity across the biosphere, the temperature rose an estimated 8 degrees C over around 100 centuries. A 4 degree C rise over 2 centuries is a rate of warming 20-30 times faster than that. At that rate of warming regions would experience months some 10-15 degrees above normal. Ecosystems would implode and be obliterated. The services they provide that sustain us would be vanquished. Virtually every vertebrate species on Earth would disappear, along with most plants and many invertebrates. I cannot say in strong enough language what the planet will look like. It will be hell for sure. What is clear to me from reading a good proportion of the comments on this thread is that people are oblivious to our dependence on the complex adaptive systems that permit us to exist and to persist. Toying with the extreme outcome of the current experiment is both dangerous and absurd. It is like proposing that a patient can survive with a prolonged fever with a temperature of 42 degrees. Not a chance.

  65. Pingback: 2019: A year in review | …and Then There's Physics

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