46 thoughts on “Climate change and catastrophe

  1. Thanks for trying to enlighten people of this doublethink on risk John.

    Beyond this I’d like to see comments on/analysis of the related risk issue of the less likely but far more catastrophic runaway Greenhouse issue that drives 350.org or at least James Hansen.

    I used to ‘feel’ this story was excessively panicky until I recently read an older (2006) less politically colored Astronomy text on the Venusian Greenhouse and likely past events there which could be twinned with earth’s future history. In case you havent encountered all of them the key points it made (especially the first) were:

    – The average temperature of Venus without an atmosphere would actually be -35 C (v. current 456 C) so the atmosphere is critical to explaining this enormous difference which I hadnt fully appreciated. Put simply Venus is not inherently uninhabitable because its simply closer to the sun.
    – The change probably only came 750 million years ago – not so much compared to the age of the solar system presumably due to slow warming of the sun tipping it over the threshhold. So the present temperature is likely the result of a very small marginal increase in solar temperature triggering Greenhouse feedback processes.
    – At a certain point in warming of a planet water vapour comes to dominate in the upper atmosphere and UV (controlled by the Ozone layer) starts splitting water much faster leading to hydrogen escape at excessive rates triggering a feedback heating loop.
    – The loss of water clamped eventually led to cessation of tectonic plate movement and accumulation of most CO2 in the atmosphere instead of minerals – Venus has the same CO2 amount as earth.

    The trouble is we dont know exactly where that tipping point is at present.

    I used to think if we were stupid enough to cause a major extinction event life would recover as it has in the past as there are microbial forms capable of growing up to 150 C and animals capable of standing temperatures in the high 40s and so a warmer average global temperture of say 20-30 C might deservedly do us in but the planet would still recover.

    This set of factoids for Venus however suggests the climate tipping point may be closer than we realize (Hansen’s expressed these concerns at seminars a few years back). Put another way there is a risk we may be much closer to the edge of the Goldilocks zone than is appreciated.

    Should we take this low risk seriously? Your rationale suggests very much yes though I’ve not seen it as having a high profile to date – usual problem of we are focused on the short term and discount the future – a flaw in our thinking/economics?.

    Now its true earth has experienced much higher temperatures around 70 million years ago. But the sun has certainly increased in temperature, CO2 has dropped, the current thermostat is set low by Ant/arctic geography which we are undermining – dark oceans and land masses absorb much more light than the present ice/snow covered geography. Separately there are the fixed carbon and oceanic methane deposits whose relese would potentially accentuate our own carbon burning effects which I understand is alone 4-6 C as you point out.

    The above is somewhat different to your article’s topic – but it is also about manging and responding to risk – specifically its the problem of how to deal with catastrophic risks which we are much less good at because of short termism – very low likelihood but impacts so profound that nothing else matters. This needs to be part of the discussion as well I suggest.

    At the very least there needs to be accelerated work aimed at resolving the runaway greenhouse question or at least improving the risk estimates. Modelling is one way but interestingly astronomy may be our best bet….to ask using the new generation of telescopes whose cost is trivial compared to available resources – are there extrasolar planets with warm liquid water or do we only see low temperature watery planets because only a temperature in the 10-20 C range is stable?

  2. Lukewarmists and others are constrained by the accuracy of data and the accuracy of their interpretation of data. What remains unassailable is the actual measurement of atmospheric CO2 and the application of the Arrhenius equation.

  3. In reality, we are still in an ice age and simply in an interglacial period of this ice age.

    “Glaciologically, ice age implies the presence of extensive ice sheets in the northern and southern hemispheres. By this definition, we are in an interglacial period—the Holocene—of the ice age that began 2.6 million years ago at the start of the Pleistocene epoch, because the Greenland, Arctic, and Antarctic ice sheets still exist. – Wikipedia.

    I doubt that there are real dangers of runaway climate change in this cycle, including the effects of anthropogenically generated free CO2 in atmosphere and ocean. However, we don’t need runaway climate change to wreck the human economy and human civilization. We don’t need runaway climate change to send homo sapiens extinct. All of these events can occur at CO2 levels much less than those that would induce runaway climate change.

    “Human civilization has developed during an extremely rare climate, geologically speaking, one with large-scale ice sheets at both poles. Only recently have we begun to understand that what we think of as “normal” climate is not in fact normal (see main story). Earth’s climate changes perpetually, far beyond the limits known from the modern and near-modern worlds.

    That Earth’s climate has lurched to extremes far beyond human experience consoles some people — why worry if extremes lie within Earth’s comfort zone of natural variation? But with our carbon dioxide output rising at an unprecedented rate, we are now exiting the comfort zone of human experience, following an accelerated synthetic path. The planet is warming perceptibly, and globally averaged temperature projections forecast an increase of several degrees Celsius within the century. The outcome of forcing the planet into a “greenhouse” during what is otherwise an “icehouse” is currently beyond prediction.” – G.S. (Lynn) Soreghan and Walter S. Snyder.

    The import of the above is that we tamper with the current atypical Holocene climate at our peril. The bigger cycles are currently well beyond our power and knowledge to affect positively and probably always will be. It is however in our power to wreck the “Holocene benignity”. It is also still in our to power (just) to not wreck the “Holocene benignity”. That is what we should be aiming at which; means getting CO2 levels back below 350 ppm CO2e and maybe even back to 280 ppm CO2e.

  4. The comments on that piece are interesting.

    The first one is “what about the pause?”, there are a lot discussing “the models” and most also include “adaptation (implying BAU)”. There’s some “population” scattered in there too.

    It’s interesting (thinking of LTG threads here which are the inverse) that in that column it is the OP which is “doomer” and it is the comments that are “Pollyanna”.

  5. JQ, I am interested in your take on the Pindyck line, which is summarised in this abstract from a 2013 paper of his:

    A plethora of integrated assessment models (IAMs) have been constructed and used to estimate the social cost of carbon (SCC) and evaluate alternative abatement policies. These models have crucial flaws that make them close to useless as tools for policy analysis: certain inputs (e.g., the discount rate) are arbitrary, but have huge effects on the SCC estimates the models produce; the models’ descriptions of the impact of climate change are completely ad hoc, with no theoretical or empirical foundation; and the models can tell us nothing about the most important driver of the SCC, the possibility of a catastrophic climate outcome. IAM-based analyses of climate policy create a perception of knowledge and precision, but that perception is illusory and misleading.

    I find this argument pretty appealing, for various reasons: the global effects of climate change are much more readily modelled than regional effects, yet economic forecasts must surely be based on estimates of its regional effects (I would assume, at least); how precisely can you estimate the cost of various types of weather disaster anyway (with, for example, one the clearest earliest effects of AGW being a rise in intense rainfall and flash flooding that could be devastating even to major cities such as Tokyo); and as for forecasting economic growth over many decades, it seems improbable that estimates made in 1900 for the economy in 2000 could give any idea of the ups and downs caused by unpredictable events of all types.

    Yet your argument at The Economist seems to offer the comfort that 2 degrees is not such a big deal for economic growth.

    Of course, I’ve no idea of the detail of how IAMs work, but I have to say, Pindyck’s line that well intentioned economists have sort of been fooling themselves (and the public) about the accuracy of their estimates of AGW on the economy makes intuitive sense to me…

  6. @steve from brisbane
    I should add: I can certainly see the value of economists’ advice on the cheapest and most efficient way to push an economy towards low carbon; what I am querying is whether economists can really claim accuracy in their estimates of how different policy approaches will affect long term GDP in the way they do, and the IPCC has endorsed.

  7. The central estimate of the IPCC for the economic cost of a transition policy consistent with the 2 deg cap was 0.06% off the GDP growth rate, or nothing within the margin of error. The lukewarmists can only get their high net cost by cherry-picking. But the IPCC bizarrely left out the health costs of air pollution, on perfectionist methodological grounds. These are gigantic: $3 trillion per year according to UNEP. These are GDP costs, not involving iffy calculations of the intrinsic value of polar bears and coral reefs. An energy transition eliminates almost all air pollution (there would still be some from synfuels in planes and bulldozers). An honest estimate of the costs of the transition must now be that they are negative, hugely negative. It’s the biggest free lunch in history.

  8. John Quiggin,

    I think your discussion of risks in this sort of area was interesting. I do not really understand statistics, but even some risk would seem to me to invoke the precautionary principle legally.

    There were two coastal climate litigation cases in Gippsland which involved the precautionary principle:

    “The current policy platform requires a precautionary approach when considering the impact of climate change. We have had regard to expert evidence which indicates that by 2100 without mitigation measures, there will be no dune, no foreshore access, no road and the subject site will be inundated by sea water and otherwise lost to use for the purpose of a residential lot.

    In the absence of any strategy or work being undertaken in the Waratah Bay area on how the issue of climate change, rising sea level and increase in storm surges is to be addressed, including what mitigation works may be necessary and undertaken, we adopt the precautionary approach of the General Practice Note (December 2008). We cannot support a subdivision in the knowledge that without mitigation works, there will be no dune, no road, no access to the site and the site is likely to be inundated with sea water. To grant a permit in such circumstances would result in a poor planning outcome that will unnecessarily burden future generations.

    Common sense tells us that, following this approach, the Tribunal should not approve coastal developments that are likely to be unduly threatened by future flooding and/or coastal inundation, creating a mess to be dealt with by future generations.”

    So in that case VCAT found that a subdivision could not be granted, due to the precautionary principle.

    But if you extrapolate from that, the precautionary principle should also be able to be invoked, along with other laws, to get the government to have to make appropriate climate change policies.

  9. There seems to be starting disillusionment with our “new government” as being “business as usual”. The picture of our new PM proudly holding his grandchild stands out. Unless it is recognised that the Industrial Revolution driven by fossil fuels is in its terminal stage, the future of that little child’s generation will be very uncertain. A new industrial revolution fuelled by renewable energy now seems eminently possible. Our environment is an immensely complex Complex System and these are characterised by self-organisation and emergent behaviour plus non-linear outcomes and thresholds, so we cannot predict the exact future except that the description of Greenhouse over 100 years ago by Arrhenius as already described in these comments indicates that, without radical change, it will not be benign. Change for the worst, already happening, may worsen dramatically and suddenly. So may change for the better if a future without fossil fuels, a new Industrial Revolution, develops rapidly. I have no economic training but I wonder, if a new Industrial Revolution does occur, those who have figured this out first will lead an economic recovery and those like Australia that lag behind will continue to lag behind.

  10. It’s also worth noting that discount rates in many of the economic models interact strongly with our assumptions about when damage from climate change will happen. If these models incorporate uncertainty on the time scale of damage (i.e. allow it to happen sooner) then the cost estimates blow out massively through the mathematics of the discount rate.

    Given that we know the current models are underestimating the rate of loss of arctic sea ice, and our understanding of the effects of this loss on weather-related disasters is still weak, it’s very dangerous to assume that the effects of climate change are a generation away. They’re happening now, and this urgency is not, I think, being incorporated into most of the luke-warmists’ assessments of the economic damage.

  11. Those building the biblical Tower of Babel, intending to reach heaven, did not know where heaven was and hence when the project would be finished, or at what cost. Those setting out to solve the climate change problem now are in the same position. If we were to spend 10 or even 100 trillion dollars mitigating carbon dioxide emissions, what would happen to the climate? If we can’t evaluate whether reversing climate change would be value for money, why should we bother, when we can clearly identify many and better investments for such huge resources? The forthcoming Paris meeting on climate change will be setting out to build a modern Tower of Babel.

  12. If we can’t evaluate whether reversing climate change would be value for money, why should we bother, when we can clearly identify many and better investments for such huge resources?

    Given the projected massive flooding as sea levels rise, droughts, flash floods, massive ecological disruption, huge numbers of refugees, and a few other calamities, some of which we are already all seeing, just where are your better investments if we switch resources from climate mitigation?

    There may be no exact certainty about what the mitigation will achieve; we know what happens if we do nothing.

  13. @chrisl
    Chrisl: Why should we spend anything at all? The cost is negative. If you think the IPCC have got it wrong on the negligible net costs excluding health, and UNEP and the WHO have got it wrong on the very large health damage from fossil fuels, kindly enlighten us with links to multiple peer-reviewed papers.

  14. @jrkrideau

    “just where are your better investments if we switch resources from climate mitigation?”

    I am sure “chrisl” is referring to beachfront real estate development, casinos, tourist traps, coal mines to power glitter strips and other highly useful investments which will stand the test of time and enrich us for generations to come.

  15. Chrisl,

    You may not have noticed, but man has reached the heavens, and found zero evidence for a God. All they have found is physics at work. This very physics are what we are deploying to understand climate change and address it, and it is all very do-able. One thing about all of this is how the Denialists have become the new “alarmists”. This “they are spending money to save the world” hashtag is the last ditch effort from the CSD (contrarian skeptical denialist) brigade, and like every other aspect of their twisted ideology, it is a contradiction of logic. A global effort to reduce carbon emissions represents global trade and every dollar “spent” is economic activity that the global economy desperately needs. Every joule of energy from the sun that is used directly to do work in place of fossil fuel used in the past for the same work represents an efficiency gain of at least 300%.

    The tax money being “spent” to protect the environment is MY money, not theirs. My money also pays for schools, hospitals, parks, and community facilities. THEIR tax money, CSD money, is spent building submarines, missiles, paying security guards and on lavish handouts to coal miners.

  16. @BilB

    Yes indeed. One of my arguments is that we can take the efficiency of the electric engine (80%) compared to the IC engine (20%) as a proxy for the general efficiency of an electrical economy compared to a fossil fuel economy. An electrical economy will do 4 times (400%) the useful work with the same amount of energy. This means that an EROEI of 10 to 1 in an electrical economy is as productive as an energy return of 40:1 in a fossil fuel economy. It took me a long to time to realise this but I think it is a key fact of fundamental importance to the whole debate. I haven’t seen any other source mention this key fact. I arrived at it independently although as I say it took me a long time to “suddenly” realise it.

  17. And when you ask ’em, “How much should we give?”
    Ooh, they only answer “More! More! More!”, y’all

    John Fogerty

    plus ça change, plus c’est la même chose.

    Jean Fogerty

  18. The dirty little secret hidden behind all the synthetic panic over climate is that politicians don’t want their programs and policies to work. They fail by design. That failure is used as an excuse to grow government, increase spending, and to aggrandize ever more power and control into the hands of the central authority: the politicians. Hence, the most important attribute of the climate models is that they DON’T work. If they really did work, the politicians wouldn’t be interested in them.

  19. @chrisl

    Are you saying:

    Climate change isn’t real?

    It’s real but not caused by CO2?

    It’s caused by CO2 but not the CO2 produced by industrial activity?

    It’s real, and caused by industrial activity but there’s nothing we can do about it?

    It’s real, and caused by industrial activity, and we could do something about it but we must not because – money?

    It’s real, it’s caused by CO2, it’s caused by industrial activity, we could do something about it but we must not because the market will decide if and when to do anything and then the market will decide what to do?

    Back to your first point: Why should we spend $1, never mind 10 or 100 trillion dollars, “mitigating carbon dioxide emissions”? We don’t need to spend a cent. We just need to massively reduce them or halt them altogether – banning them would be the best option, like CFCs, but taxing them into extinction might work. Creating a “market” in them is doomed to fail, however, IMO.

  20. Chrisl,

    You really are a long way down the Libertarian rabbit hole. Putting climate models and governments to one side for a moment, you must go to a lot of effort to not here the ever increasing flow of news of the effects of climate change, particularly where it causes visible change.

    The expanding tropical zone causing species of all kinds to move further poleward. The recent announcement to reactivate prehistoric viruses in order to study them in preparation for their inevitable release as Arctic permafrost melts. The rapid spreading of tropical insects and diseases. The impact on bees as plant species suffer with climate change. The list is huge and spells out catastrophe for humankind. Those threats on their own should be sufficient to justify a massive action to prevent their advancement, and fortunately the world is mobilising.

    The problem with your thinking, Chrisl, is that you believe that climate change action will cost you money. The fact is that the world will take climate action and do so at a profit. Ikonoclast supports that argument with his comments on electrification and energy costs. It is energy policies that got us into this mess, along with population size, and it is energy policy that will get us out of it. And in the so doing we will turn a national profit while improving our standard of living.

    It is all good. Importantly though I do not feel disadvantaged that you will benefit from my investment in the environment, and I forgive you for not understanding any of this.

  21. @chrisl

    By your predictions, investors who divest from coal mines and beach front property are leaving you with a great investment opportunity. Be our guest.

  22. Chrisl may have one point correct – politicians in Australia and other fossil fuel rich nations tend not to want climate policies to work. Appearing to have climate policies whilst not endangering the projected incomes from future resource extraction, avoiding the difficulty in developing and selling in depth policies for a transition away from high emissions energy whilst appearing to take science based climate concerns seriously, advocating on behalf of major corporate interests who are major campaign funds contributors with extensive lobbying power and who threaten economic mayhem if they don’t get their way whilst maintaining the public appearance of being responsible and trustworthy in positions of authority… ie wanting climate policies that don’t and won’t work. Preferably they seek to do this whilst shifting blame for policy inadequacies to those who advocate most strongly for effective action, like Environmental advocacy and The Greens.

  23. In the paper I linked to at comment 19, there is a hypothetical graph on page 38 which basically posits that;

    Technological progress is faster than business progress which is faster than social progress which is faster than political progress.

    I find this pretty much accords with what I am seeing. Political progress in contemporary society is glacial and far behind what is becoming possible on the other leading fronts.

    Note: I would probably argue though that social progress is now ahead of business progress. The majority of people have wanted climate action progress for some time but business (read corporate capitalism) closely allied with reactionary politics has obstructed this progress.

  24. I haven’t had time to go through that item, Ike, but at a glance it looks like a very interesting and useful body of information. I am going to stick my neck out here, though, and suggest that the 2 most rapidly adopted technologies in recent times, rivaling even TV’s, are the smart/cell phone and the solar panel.

  25. To a surprising extent, climate policies actually are working, as anyone who holds shares in a coalmining company can tell you.

  26. Ken Fabian,

    The problem with that thinking is that it is extremely short sighted. The coal that Australia has left will be worth 10 times more per year over the next 2 millenia as a building material. Carbon is in the structure of nearly everything that consider to be useful. It is in the plastics and epoxy resins. It is the substance that electronic circuit boards (along with silicon) are made of, our cars of the future will be predominately carbon, carbon, silicon, ceramics, calcium and highly process metals are the building blocks of a technological future, and yet we squander them. There are those Australians who would scrape out every last chunk of carbon today only to enrich themselves if they could. We can’t let that happen. Once dispersed into the atmosphere and subsequently the biosphere, the Carbon will be very expensive to claw back. We need to keep most of it in the ground now for the future of this technological civilisation.

  27. To what extent is coal mining share price a consequence of climate policy? Climate policy may have kick started the renewables cost plunge but I suspect it began as more about appearances than conviction and perhaps supported – or tolerated – in an expectation of failure. Solar as cheap as chip wrappers and batteries to go with it might be credible for achieving emissions reductions at a scale needed but I’m not convince any science based foresight and planning from policy makers, at least from mainstream Australian politics, is capable of much beyond policies that look good but don’t hurt the resources sector. A bit cynical I know.

  28. @Ken Fabian

    We’ve seen large numbers of coal-fired power stations closing down as a result of climate policy in the US, China and Europe, new finance for coal cut off by development banks, projects like Adani blackballed and much more.

    It’s true that Australian governments haven’t exactly led the charge, but the Renewable Energy Target has at least ensured there will be no new coal-fired power stations for the foreseeable future.

  29. There is a lot of detailed information here for recent and imminent retirements of US coal power plants (of about 340,000MW existing, 25,000-60,000MW to be closed).

    Rather than Climate Policy, cheap gas (especially the fracking “boom” – which is a finance Ponzi scheme and environmental disaster) is the more likely main driver.

    People haven’t suddenly stopped using the coal-fired electricity they were using a few years ago. I would suggest that the main reason for the collapse of coal price is the economic collapse happening right now, especially Chinese industry, and finance driven resource speculation and over-production at unsustainable prices.

    Speaking of which:

    JQ – What is the preferred data source or measurement of current and historical per-capita industrial output?

  30. @chrisl
    Not sure what the tower of Babel has to do with this, or anything else.

    Assuming it’s not totally mythical, the tower’s collapse had more to do with a poor understanding of engineering principles than an open-ended budget or an angry deity. After all, if you try to build a mud brick ziggurat with a slope steeper than the slump angle of soil, you’ll end up with a catastrophic failure.

    Come to think of it, that’s not a bad metaphor for the denialists’ efforts. Just substitute bullsh!t for adobe.

  31. Assuming it’s not totally mythical, the tower’s collapse had more to do with a poor understanding of engineering principles than an open-ended budget or an angry deity.

    See, I thought it was about the difficulties of managing complex multi-national civil engineering projects.

  32. @chrisl

    I posted some questions to you at #21.

    As an aside, your interpretation of the myth of Babel isn’t how it appears in the old testament.

    Wikipedia has an entry about it and this is about right:

    The story of the city of Babel is recorded in Genesis 11:1–9. Everyone on earth spoke the same language. As people migrated from the east, they settled in the land of Shinar. People there sought to make bricks and build a city and a tower with its top in the sky, to make a name for themselves, so that they not be scattered over the world. God came down to look at the city and tower, and remarked that as one people with one language, nothing that they sought would be out of their reach. God went down and confounded their speech, so that they could not understand each other, and scattered them over the face of the earth, and they stopped building the city.

    Apart from the observation that this “god” character is one seriously messed up personality, the original story has nothing to do with the project failing on the basis of completion date, cost or specs. It failed because of malicious interference in the means of communicating information between the parties involved.

    Hey….. just a minute…, there IS a parallel with reducing carbon emissions!

  33. @chrisl
    Well, you brought up the Tower of Babel, although I don’t have any idea what point you were trying to make. Perhaps you could clarify that for us simple, reality-focussed, folk.

  34. They had Barnaby on Q&A the other night. Talk about ignorant. He had the idea that the main reason a Carbon price reduced emissions was because the increase in the price of electricity reduces demand.

    Unfortunately, no-one pointed out to him that the main reason a Carbon price reduces Carbon emissions is because it makes energy production (including electricity) using non-Carbon burning sources more attractive than otherwise, so Carbon emissions fall mainly because of a shift in energy production from Carbon-burning to non-Carbon-burning sources.

    It’s a sad reflection that not only did Barnaby not know this, but no-one on that program pointed out his error. It’s just another case of “Australia is a lucky country run by second rate people who share its luck.” Barnaby is just another one of those second rate people who run the country.

  35. @Chris O’Neill

    Barnaby is second rate? Methinks you praise him mightily beyond his real ability. I’d call him a sixth-rate. That was the lowest rate of vessel in the old British Navy (wood and sail); so on that general analogy he is a sixth-rate. Actually, I don’t think he is worth the un-planked frame of a beached and rotting jolly-boat.

  36. @Newtownian

    At a certain point in warming of a planet water vapour comes to dominate in the upper atmosphere and UV (controlled by the Ozone layer) starts splitting water much faster leading to hydrogen escape at excessive rates triggering a feedback heating loop.

    I think in the case of Venus (also Mars), the water was being lost through UV decomposition and subsequent loss of hydrogen to space all through its history because there was never a significant amount of Ozone compared with Earth’s oxygen-rich atmosphere. Of course, Earth’s atmosphere only became oxygen-rich in the last billion years so this was only a relatively recent factor in reducing the loss of water from the Earth. So the heating of Venus was probably an important factor in speeding up its rate of hydrogen and thus water loss.

    At the very least there needs to be accelerated work aimed at resolving the runaway greenhouse question or at least improving the risk estimates.

    Regarding “runaway” greenhouse warming, I believe the climate sensitivity increases with increasing oceanic surface temperature and reaches the point of instability or “runaway” somewhere around a water surface temperature of 60C – not something we need to worry about anytime soon, we’ll be in dire straits from the effects of global warming long before that temperature arrives, but something to think about. Even if sensitivity did not increase with temperature, it would only take 10 doublings in CO2 (1,024 times) to reach runaway global warming. A rough calculation assuming climate sensitivity is inversely proportional to the difference between 60C and maximum ocean surface temperature would suggest 6 CO2 doublings (64 times) will take global warming to runaway. So perhaps something over 2% CO2 in our atmosphere would be enough to reach global warming runaway.

  37. @chrisl

    Those building the biblical Tower of Babel, intending to reach heaven, did not know where heaven was and hence when the project would be finished, or at what cost.

    Much like the Liberal Party’s “direct action” scheme for reducing Carbon emissions. Barnaby on Q&A helpfully pointed out that there were no estimates for how much “direct action” would cost taxpayers to reduce Australia’s GHG emissions by 28%.

  38. @Chris O’Neill

    The Skeptical Science site notes;

    “Atmospheric CO2 levels have reached spectacular values in the deep past, possibly topping over 5000 ppm in the late Ordovician around 440 million years ago. However, solar activity also falls as you go further back. In the early Phanerozoic, solar output was about 4% less than current levels.”

    If I have got my decimal places right, 5,000 ppm = 0.5%, which is still way below the danger mark of over 2% CO2 for runaway global warming, if that is a correct figure.

    However, “runaway” change to a new climate state (rather than to a boiling state) can still occur well below this level and might even be possible at current levels of 400 ppm or 0.04% CO2.

    The Holocene (where we are now temporally) is actually an ice-age, hard as this might be to believe. We are simply in an inter-glacial period (glaciers retreating). The last glaciation, the Quaternary, occurred during the last one hundred thousand years of the Pleistocene, from approximately 110,000 to 12,000 years ago. Cultivation and civilization essentially developed and evolved in an ice-age inter-glacial and are thus arguably adapted to it and to the relative general stability of the current Holocene climate. However, current climate forcing from anthropogenic CO2 may well end this ice-age with a rapidity usually reserved for catastrophic events like massive volcanic shield outpourings of CO2.

    It’s not runaway global warming to a boiling planet that we have to fear even in the next several million years. It is runaway climate change (with some warming obviously) to a new climate state. The period of state-change would see massive instability and fluctuations in many climate and weather parameters. The new eventual state, with new ocean currents and new wind and air circulation patterns would throw just about every climate verity we currently rely on, right out the window basically. For example, current monsoons and their reliability could alter profoundly thus affecting the viability of tropical and sub-tropical agriculture for billions.

  39. @Ikonoclast

    However, “runaway” change to a new climate state (rather than to a boiling state) can still occur well below this level

    You can make any definition for “runaway” you like but the usual definition is where the feedback produces a marginal climate sensitivity of infinity. That won’t happen until the ocean surface temperature reaches around 60C. But as I said, we are in dire straits long before that happens. You don’t need runaway global warming to be in a disastrous climatic situation.

    BTW, using the term “runaway” global warming for anything less than the usual definition of runaway global warming simply leaves you wide open to claims of alarmism. Better just to stick to the usual definition.

  40. @Chris O’Neill

    using the term “runaway” global warming for anything less than the usual definition of runaway global warming simply leaves you wide open to claims of alarmism.

    or accusations of alarmism.

  41. @Chris O’Neill

    Actually, I used the full term “runaway climate change”. The sense is “rapid climate change until it reaches a new stable condition”. The term to imply runaway to boiling or at least to some catastrophic and irreversible heat level is “runaway greenhouse effect”. At least, that is how I understand matters.

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