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Eocene Park: our experiment to recreate the atmosphere of an ancient hothouse climate

Posted on 6 April 2012 by Andy Skuce

Fifty million years ago, during the Eocene Epoch , the world had a very different climate, with temperatures much higher than today's, especially at the poles. This hothouse climate was caused mainly by CO2 levels that were twice as high, or more, than now. On our current emissions trajectory, we could recreate the chemistry of the hothouse atmosphere before the end of this century, with potentially drastic consequences for our climate.

The Hothouse

Imagine a world where crocodiles swim in an Arctic ocean among blooms of freshwater ferns, and where palm trees grow in Alaska and the high valleys of the Rocky Mountains. In this world, a great forest covers the continent of Antarctica and there are no large ice sheets. Sea levels are 50 metres or more higher than today’s. This world was the hothouse Earth in the time of the Eocene Epoch, 56 to 34 million years ago.  Estimates of the concentration of carbon dioxide in the Eocene air show that they were two times or more higher than today. Such a CO2-rich atmosphere has not been seen since the Eocene, but it is quite possible that we will create an atmosphere like it again soon, perhaps later in this century.

The frost-intolerant palm trees that grew in Montana show that that Eocene winter temperatures, even at high elevations in mid-latitude continental interiors, must have stayed above zero most of the time.  The variation of average temperature with latitude—the poles in the Eocene were 30°C warmer than today but the tropics were only a few degrees warmer—is another characteristic of the Eocene sauna. Trying to model this climate presents a challenge known as The Equable Climate Problem.  Higher levels correctly predict a much warmer world but there are some mismatches in the regional predictions. In essence, the difficulty is that if the boundary conditions in the climate models are set to values that produce mild winters in continental interiors and high latitudes, the modelled tropics turn out to be hotter than our best proxies show. However, the discovery of a one-ton fossil snake in Colombia suggests that Eocene and Paleocene tropical temperatures may have been underestimated.  Many innovative solutions (see page 243 of Huber and Caballero (2011) for a referenced list) have been proposed to resolve the Equable Climate problem but there is, as yet, no consensus on a resolution.

The Eocene hothouse and the elevated CO2 levels came to an end in the Oligocene Epoch and the Earth’s climate changed into its current icehouse state.

Drifting into the Icehouse

Large ice sheets formed in Antarctica starting 34 million years ago, then, later, on Greenland —about 3 million years ago—and in North America and Northern Europe within the past million years. This climate transition was partly controlled by the movements of the Earth’s tectonic plates. The rifting and drifting continents built mountains that drew down the CO2 in the air (by means of the Weathering Thermostat, see here, section 2.4 and here after 22 minutes) and changed the configuration of the oceans, altering the way that heat was distributed around the planet. John Mason's SkS post The End of the Hothouse has more details.

The main tectonic events were:

  • The opening of the Norwegian-Greenland Sea, around 50 million years ago, ending the near-isolation of the Arctic Ocean.  This terminated the Azolla phase of the Arctic, in which blooms of the freshwater fern Azolla may have been responsible for absorbing and sequestering large quantities of carbon dioxide during the Eocene. Further reading herehere and here. The North Atlantic Igneous Province, which produced basalts from Scotland to West Greenland also came to an end around 54 million years ago. These volcanic eruptions contributed considerable CO2 to the atmosphere in the Paleocene and early Eocene.
  • The collision of India and Africa-Arabia with Eurasia, raising the Himalayas and exposing crystalline rocks to weathering.  Chemical reactions between silicate minerals and CO2 gradually reduced the concentration of this gas over millions of years. The Himalayas have a long history going back far beyond the Eocene and actively continuing to this day, but the big event was the continent-on-continent collision that started around 45-55 million years ago.
  • The opening of the Drake Passage between South America and Antarctica, as well as the northward drift of Australia; together allowing the Antarctic Circumpolar Current to form. This current keeps warm ocean water away from Antarctica and is a crucial part of the ocean conveyor system to this day.

The Earth’s geography 50 million years ago. Modified from Wikipedia, to highlight (red arrows) the plate movements that influenced the changing of the Eocene hothouse into our current icehouse climate.

The change in climate after the Eocene spurred the evolution of the grasses, which adapted to the cooler climates and lower CO2 conditions over 40 million years.  Grasses co-evolved with the large grazing animals. The domestication of certain species of both these grasses and grazing animals led to the invention of agriculture and the consequent explosion of civilization during the stable climate of the past 10,000 years.

Measuring the Eocene Air

Thanks to the tiny bubbles frozen into ice cores, we have samples of the Earth’s atmosphere going back about 800,000 years.  To look back further in time, we need to use proxies: indirect observations of characteristics of fossils and sediments that provide evidence of past CO2 concentrations. These estimates have large error bars. Different proxy methods have produced widely different estimates, sometimes by as much as a factor of ten.

A recent compilation of proxy measurements over the last 65 million years by Beerling and Royer (2011) finds a much better agreement among the methods. But despite the reported improvement, a two-fold level of uncertainty remains.

Modified from a figure by Beerling and Royer (2011), showing proxy CO2 estimations, deep-sea temperatures, the formation of the Antarctic ice sheet, the current CO2  level (dashed line) and the range of  CO2 variation observed in the ice-age (grey bar on the right) . The unmodified figure, with original caption can be viewed here. The green annotations on the right-hand side have been added to show 2100 CO2 levels in IPCC SRES projections, ranging from the optimistic B1(ecologically friendly growth)  to the pessimistic A1FI (rapid growth and reliance on fossil fuels).

Beerling and Royer urge researchers to focus on calibrating their results to the last 800,000 years, a period for which we have samples of past atmospheres. While such work would probably improve confidence in the proxies, uncertainty will remain for the proxy-measured CO2 concentrations that have much higher than modern values. Huber and Caballero (2011) point out that some proxy measurements in the Early Eocene are more than 2000 ppm of CO2 (e.g., Pearson and Palmer, 2000). A further complication is that methane levels, for which there are no proxy estimates, may have also been high in the Eocene, contributing significantly to warming the hothouse.

The Great Leap Backwards

In a middle-of-the road IPCC scenario, A1B (rapid growth with a mix of energy sources), we could, by 2100, see CO2 levels similar to those in the late Eocene: around 700 ppm, comparable to the atmospheric conditions before the formation of the Antarctic ice sheet. In an optimistic case such as B1, which we now appear ever more unlikely to achieve without immediate emissions reductions, CO2 concentrations would rise to over 500 ppm, still exceeding anything observed in the past 30 million years. A plausible but pessimistic scenario, A1FI, would see 2100 CO2 concentrations rise to 1000 ppm, comparable to atmospheric conditions in the Early Eocene, which was the hottest time in the past 65 million years, apart perhaps from the short-lived (geologically short, that is) spike in temperatures at the Palaeocene-Eocene Thermal  Maximum.

Perhaps the most astonishing aspect of the change that we are currently inflicting on the atmosphere is how fast it is happening. It took 40 million years to go from 750 ppm to the pre-industrial level of 280 ppm of CO2. To leap back to the Eocene atmosphere may take us just 200 years, some 200,000 times as fast.  That’s roughly the same difference in speed between a snail and a jumbo jet. Of course, the climate will not fully respond to this sudden shock immediately; there is inertia in the system, fortunately. It will take many hundreds of years for the oceans to heat up and many thousands for the ice caps to melt completely. 

Even though it is the biggest control knob, CO2 is not the only factor governing the climate; the level of output of the sun plays a big role and many other elements, for example, the reflectivity of the surface and the redistribution of the heat throughout the Earth by ocean currents are also important. An analogy might be what happens when you turn up the furnace in a home: how hot the house gets may depend not only on the furnace setting but also on how strongly the sun is shining outside; how hot individual rooms may get will be influenced by whether or not interior doors are open and if the heat can circulate freely.

Welcome to Eocene Park, currently under construction

The science-fiction novel Jurassic Park recounts a mad experiment in which dinosaurs are cloned from fossil DNA and allowed to roam free on a tropical island in the Pacific. The story is a cautionary tale about how tinkering with nature leads to unexpected and disastrous consequences. (Ironically, Jurassic Park’s author, Michael Crichton, went on to write the climate-denial novel State of Fear.)

Performing a great leap backwards to the Eocene atmosphere will produce all kinds of unexpected consequences.  There are big uncertainties, both with the Eocene CO2 proxy measurements and with the climate models. Nobody can say for sure how events will unfold; perhaps things will be hotter, perhaps cooler, than the Eocene analogue. Maybe the new climate will be equable, with most of the extra heat at the poles; maybe it won't. Today’s Earth is not the Eocene Earth: the oceans are plumbed together differently, the biota is changed, orbital configurations may vary slightly and there are billions of us humans who have altered the face of the land. Ecosystems and organisms will have to adapt to our new world at a pace faster than a snail's. Moreover, the planet’s reservoirs of carbon in frozen northern soils and in rainforests as well as in gas hydrates are now charged up and, quite possibly, prone to release into the atmosphere as the climate warms. These feedback emissions would make an already bad problem even worse.

Creating an outdoor Jurassic ecosystem on an island is the stuff of science fiction. Yet, our current business-as-usual policies are rapidly recreating the fundamental characteristics of the atmosphere of the Eocene. In Jurassic Park, the fictional Costa Rican air force solved the problem by blowing up the island, but that is hardly an option for us: there's no Planet B. The Eocene Park project is not a work of fiction. The Keeling Curve has not been drawn on an Etch-A-Sketch.

We are not entirely sure quite how badly our Eocene Park experiment will turn out.  But, uncertainty, we must remember, is not our friend


[Thanks to Sarah and Sphaerica for their comments on an earlier draft.]

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Comments 1 to 33:

  1. Thanks, Andy. two remarks: At least the locations of continents are different today. It may take a little more rise in the concentration to melt the (whole) Antarctic ice sheet (however long it'll take). Do you know are there much differences in north Atlantic currents if one compares early Miocene (when there was a Panama Strait instead of a Channel)and Pleistocene/start of the Anthropocene? One would like to think the closing of that strait lead to cooler temps in the Arctic so it might be the concentration to melt GIS would also be higher than the last time. But by how much, I can't say. Might be even lower if the tropical Atlantic heats up by some mechanism induced by shifting atmopheric phenomena.
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  2. One of the most interesting (and important) posts I've read here. Many thanks.
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  3. Good article. Of course as part of our irreversible experiment to recreate the Eocene we need to start selectively breeding all current mammals to be the size of small rodents -- oh, and that includes ourselves. It seems only small mammals can handle the heat. Reptiles on the other hand... Anyone know of any small rocks to hide under?
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  4. jyyh: Thank you. No, I don't know enough about palaeo-oceanography to answer your question. Perhaps other readers do.
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  5. I am fascinated by earths past climate. And this was excellent. There was something 41 million years ago called the Middle Eocene Climate Optimum Some 40 million years ago, the world experienced an extreme spike in global warming. The heat was so intense that deep sea temperatures rose by about 4 degrees Celsius. This enigmatic sultry period, known as the Middle Eocene Climatic Optimum (MECO), marked a 400,000-year-long heat wave in the midst of a long era of global cooling.
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  6. Andy S - great article. I like this style of looking at the world, rather than the relentless focus on what incorrect thing so-and-so said (both are necessary). Very thought provoking. 200,000 times the natural rate - that is a number I will weave into "discussions" with deniers.
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  7. The fig.2 in Micheels & al. presents a vegetation proxy of miocene times and that looks like being a much wetter period than now for some large areas. It's a preprint, and I do not know if the paper has been published yet, anyway it refers to many earlier discussions on this. Could be interesting for readers to see.
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  8. John Russell pre-empted me at #3, but it's worth repeating... Mammals are not adapted to temperatures significantly higher than those of the current 'ice age'. We just aren't. In fact one reason mammality was able to evolve was because of the moderate temperatures of 'ice ages'. Any warmer, and the efficiency of the suite of counter-balancing thermoregulation adaptations starts to break down. Natural deselection... It's 'simple' thermodynamics. That the Denialati imagine that an Eocene-like climate is lovely and balmy and desirable simply shows the depth of their ignorance of mammalian physiology.
    Of course, the climate will not fully respond to this sudden shock immediately; there is inertia in the system, fortunately. It will take many hundreds of years for the oceans to heat up and many thousands for the ice caps to melt completely.
    I have one small philosophical nit-pick - it might not be "fortunate" that there is an inertia in the global climatic system. Had it been that the scale of the period of change was closer to the lifetime of a human, there might actually be more inclination to address the problem. As it is our species put its collective head in the sand, and aided and abetted by our knee-jerk response to an economic system that also ignored thermodynamics, we're already committed to a change that will likely see a human-friendly ecosystem disappear in the centuries ahead. Fortunate for us, perhaps, but not for our decendants. I've said it previously but I'll indulge again - if our decendants could manage to conquer time travel, or to reanimate the dead, they'd be post haste hunting our generation down and kicking our arses for what we're doing currently to the planet.
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  9. I also enjoyed the article thanks. James Hanson has a similar discussion in his book "Storms of My Grandchildren", in Chapter 8 'Target Carbon Dioxide: Where Should Humanity Aim'. Some interesting points - . He has a good discussion on how the temperature curve is derived and does an analysis of temperature changes Vs forcings from CO2 and ice albedo changes. His starting point in this analysis was 50mya with the temp 14 and CO2 at 1400 with uncertainty of 500. . He advised Bill McKibben to set the CO2 target at 350 based on the analysis of this period. One factor was that at 34mya when Antarctica became cold enough to harbor an ice sheet the estimated CO2 was 450 with uncertainty of 100. 'This has a clear, strong implication for what constitutes a dangerous level of atmospheric carbon dioxide' . On ocean currents he mentions that 55mya at the Paleocene-Eocene thermal maximum (PETM) there was a dramatic change in ocean circulation indicating that the main location where dense surface water sank to the ocean bottom shifted from Antarctica to middle latitudes in the northern hemisphere. It is likely that this warmer water instigated the melting of methane hydrates
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  10. Adding my two cents to what John Russell and Bernard J. already said, the distribution of human population versus temperature or, better, heat index shows a long tail toward colder temperatures but a sharp cut off at high temperatures. A temperature increase of just few degrees is enough to force milions of people to move and abandon large swats of land. Adaptation is not an option in such cases. We're risking a 21st century gold rush but there's no gold anywere.
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  11. Further to my comment @#3, Bernard's @#8 and Riccardo's @#10; incredibly, it seems like some people are ahead of us!
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  12. Bernard J @8 Yes, good point. I guess I let my pessimism slip out there, since my "fortunately" applies only to the extra time we'll get for adaptation and implicitly assumes we'll blindly carry on with business-as-usual. Climate change would be an easier problem to mitigate if it were not for the fact that many of the effects are delayed. Which, as you correctly point out, is not fortunate at all.
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  13. If I may be briefly grumpy about heat and human habitation. There's a big difference between can't survive anywhere, and must move somewhere. Humans live in decently warm places already, and the number of people displaced, eventually, because it gets unsurvivably hot is probably smaller than the number displaced because of high water (this is a pure SWAG on my part, but lots of people live on or near the coast in many countries).
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  14. Is a breakdown, or major perturbation, of the Antarctic Circumpolar Current impossible, possible or inevitable some time in the distant future? Would this then affect circumpolar winds? (I have no idea of the answers). From the little I have seen of the outputs of climate models it would appear everyone is assuming it will remain stable. If it did change, the estimates of sea level rise would have to change too.
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  15. Tony O the AAC is essentially wind driven, no major changes are projected.
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  16. There's a big difference between can't survive anywhere, and must move somewhere. Humans live in decently warm places already...
    I don't think that anyone would dispute that humans are able to live at temperatures considerably greater than the current mean global temperature. However, there are many factors involved in maintaining survival if the global mean is increased. Amongst them... 1) Many serious human diseases, and their vectors, thrive at warmer temperatures. A change toward greater incidence of disease compromises a species' capacity for survival, especially in competition with taxonomically distant taxa. 2) Whilst humans have a capacity for modification of their environment in order to regulate their temperature, the rest of the biosphere is not so fortunate. Many species on which humans rely for direct or for indirect ecological services will be negatively affected, and this will impact back on humans, even if they themselves are cloistered in air-conditioned cells. 3) In a world where fossil fuel energy density is a thing of the past, human labour will necessarily regain widespread utility. Working harder in a warmer climate will inevitably affect our species physiological fitness directly, and relative to other species. All the more so considering that a significant chunk of the industrialised world wouldn't know what hard physical work is, and because they are carrying an insulating layer of blubber courtesy of the obesity epidemic. 4) In most cases it is not the mean temperature that challenges a homeotherm, but the extremes that occur under a particular regime. An increase in mean of "just a few degrees" brings with it an increase in both the frequency and the absolute magnitude of extreme temperture events, and it is these that operate as the weak link in stressed thermostatic physiologies. 5) Human populations are concentrating in urban environments over time. Remember those heat islands? The result is an overall increased vulnerability to heat shocks. 6) Much of modern human response to heat requires technological intervention. No matter the dreams of thermodynamically-illiterate, technophilic Utopians, future human societies will have less recourse to technological intervention in ambient temperatures, especially as more and more fossil fuel is combusted to (in part, ironically) maintain current living standards. 7) Related to the previous point is the fact that global economies are beginning to shake under the manifestation of the same ignorance of thermodynamics that afflicts technosalvationists, and even a brief period of serious generalised damage to the financial system will see an accompanying decay in infrastructure - which is not likely to be easily reversed in a world where densely-concentrated energy is a thing of the past. 8) Displacement for reasons of avoiding heat stress is only a part of a greater AGW-caused displacement of other factors that affect human survival. If humans cannot bring everything else they require in their move to Cooltopia, then other aspects of the fitness for survival will be diminished. And this list is just for starters.
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  17. Many thanks to Andy S for a fascinating article. In follow-up to John Russell's comment @#11, the man who is "ahead of us", S. Matthew Liao of New York University, suggests several ways (mostly foolish, in my opinion) in which human beings might be "engineered" to diminish their impact on the climate and/or to diminish the impact of the climate on them. So far as I could tell when I skimmed through his paper on the subject, he did not suggest any method by which human beings could be made more heat-tolerant. Therefore the concerns raised by John Russell @#3, Bernard J @#8, and Riccardo @#10 still stand.
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  18. @BernardJ, #16. I remain grumpy, and your points do little to make me ungrumpy. The people who live in the hottest (hottest+humidest) places on earth now often do not have air conditioning, and often engage in manual labor. They have heat waves, too. Disease vectors need more than just favorable climate. There was a malaria epidemic in Philadelphia in 1780. The town where I went to elementary school used to be called "Yellow Bluff", but yellow fever epidemics (in Florida) made "yellow" a bad word for attracting new residents. It's not just climate; public health is a big part of it, too. We also adapt in more ways than just deploying air conditioning. I grew up, and attended college and gradual school, in some pretty hot and humid places (Florida, Houston). Growing up, I often engaged in actual, outdoor, physical activity. Your body learns to sweat, you learn to drink more, you develop shade-seeking habits, etc. When I return to the ancestral home, it takes a few days for my body to figure out WTF to do, and then it copes. These places are nonetheless well cooler than true tropics. In addition, everything I read suggests that the greatest warming will occur away from the tropics, and recently I've read that jet stream changes around the poles may be the cause of our more extreme hot/cold/wet/dry weather in recent years. Looking at current maps of maximum wet-bulb temperatures, my guess is that if anywhere becomes uninhabitable, it will be places like Iraq (already hot and humid). Brazil's future weather might be like Iraq's weather now, and perhaps Houston will become more like Brazil today, and Washington DC more like Houston. There will be much whining, but Houston is already hot, already urban, already a heat island, and people live there now. An aggressive program of painting roofs and roads white would counter the heat island effect handily at little inconvenience to residents, in Houston and in every other city. I don't think the effort to slow climate change is helped by hyperbolic "we're all gonna die!!!!" pronouncements. There are some low-probability events that really would kill us all (oceans going anoxic). If sea level rise hits the high-end estimates (5cm/year for a century or so), millions of people will need to move to higher ground. But within the predicted range and distribution of future warming (at least in this century, maybe the next), no, the heat will not be a killer. (I'm aware of the killer-wet-bulb predictions. Those are for the case of a 12C rise in global mean temperature. IPCC BAU to 2100 is +4C, right?)
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  19. dr2chase: I am sure that even in the most extreme scenarios, there will be places on the planet, at high latitudes or high altitudes, where humans will be able to live in some kind of self-sufficient manner with a modified form of our current agriculture. The question is whether these places will be large enough and connected enough to support the kind of specialized economies and trade that have raised standards of living and quality of life; at least for the most fortunate of us in developed countries. What particularly concerns me is the pace of the forced change, both for the physical environment and for our civilization. If this transition were taking place over tens of thousands of years, hundreds of human generations, I'd be fairly comfortable with it. Cities would have to be rebuilt several times over anyway, so sea level coming up fifty metres or so would be no big deal. Slow migrations and small changes in fertility could redistribute the population without major suffering. Advances in agriculture and technology would likely ease the transition. This change we are inflicting isn't a gentle wind gradually pushing the global supertanker off course, but, rather, an impact with a reef. It the suddenness and unpredictability of the coming changes that bothers me--the probably ugly consequences of forced adaptation over the next couple of centuries--not the unlikely prospect of the entire extiction of Homo sapiens in the longer term.
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  20. dr2chase. It was genuinely not my intent to exacerbate your grumpiness. Perhaps you need to understand that as an ecologist I am looking at this in a slightly different context to the "next election cycle", or the "next house move" time frames that most Western people are inclined to employ. You mention individual people's abilities to adapt to local changes. I tipped a hat to this at the top of the post at #16. Certainly, no-one disputes that individually, and at local spacial scales and at certain temporal scales (days to years), humans have an amazing capacity for adaptation, temperature adaptation included. The problem for us as a species is greater than this, however. It might be worth re-reading my previous points and dwelling on them carefully, because they encompass some profound challenges to humans that render less impressive our current abilities to tolerate extremes of heat - and indeed of any weather type. Fact: oil will run out. Functionally, and globally, probably within half a century. Social/technological unpreparedness, and the resulting social/economic havoc that will ensue as shortages start to bite, might bring the effective functional end closer than around that ball-park estimate of half a century. Our industrial food production paradigm is implacably based on the production of nitrogen fertilisers derived from fossil fuels. Without oil the easiest feedstock with which to manufacture fertiliser disappears. Coal can be converted to other forms, including synth-oil, but a lot of (currently non-existent) infrastructure is required, and there is a thermodynamic cost to deriving the converted energy density. Thus the energy-return-on-energy-invested (ERoEI) from converting coal is lower than with oil-based feedstocks, and this in itself has profound technological and economic consequences. Frankly, humans have probably already left it too late to attempt a smooth transition to a non-oil based economy, whether one is considering food production, electrical power supply, fuel-based temperature regulation in buildings, or transport. Further, without full exploitation of coal there is little chance that our civilisation as we currently recognise it will continue into the future*. Where does this leave the younger amongst us, and our yet-to-be-born decendants? Basically, without the technologies that we currently use to manufacture textiles, to generate warmth (and coolth) and to keep everyone's neighbours from eyeing off any useful thing that they might have squirrelled away. In the near future a climate that is two or three degrees warmer might simply be a bit more of an inconvenience under a contracting economic regime, but it will grow ever more noticable as the extremes impact directly on our communities, and as the ecosystem services on which we rely (including a nacently non-fossil fueled agriculture) start to through curve balls at us. We might not as a species all die of heat exhaustion (in fact, few of us will), but many are still going to be directly and severely impacted by the increased heat extremes that the planet will experience. And by other indirect extremes, such as drought and flood, that come from heating the planet. And remember that this is going to happen with a loss of ability to manufacture industrial scales of food... Even then we won't plunge directly toward extinction. We might not lose even more than, say, around half of the peak human population before we accept a much-reduced standard of living, and decide to go hammer and tongs at the coal no matter that it's a Faustian bargain. And Faustian it would be. If humans do end up burning all of the coal on the planet (and current socio-political trends indicate that we will), then the final increase in mean global temperature will be in the range of 6 degrees celcius, or more. Even if we decide to forebear our current inclination to burning coal future, more desperate generations might not be so restrained, and may not recognise the lessons of Angkor, Easter Island and other such civilisations. In a climate that warm the extent of human-habitable regions will be much reduced, and certainly heat limits to human physiology will be a significant component of this fact. Add to this the requirement for ecosystem functions necessary for human survival, and that probably require similar climatic conditions to humans, and suddenly there's little room to squeeze in much of a niche for us as a species. In the end it's a whole suit of factors that combine to make any significant planetary warming undesirable for humans. Direct physiological constraints are not the entirety of the story, but neither are they least amongst them. [*Nuclear energy is not going to save us, but that's a topic for a different discussion.]
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  21. And as an addendum, Andy S's observation about the rapidity of global warming is an important factor in how humans are - or are not - able to adapt as a species. Individuals will always be able to adapt to changes in temperature, but at the species level rapid temperature change is very undesirable. This leads to (or rather, stems from) discussions of the Holocene constancy that led to the development of agriculture and concurrently of human civilisations, but such has been described elsewhere and probably doesn't need to be repeated here.
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  22. "Direct physiological constraints are not the entirety of the story, but neither are they least amongst them." Maybe not for us. Leaving aside the issue of oil-based fertilisers, do we really know the physiological limits for bees and bats and the other small critters we rely on for crops? Our own physiological limits will be severely tested if we suddenly pass some temperature limit affecting a pollinator species for a major food crop.
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  23. Adelady: we really know the physiological limits for bees and bats and the other small critters we rely on for crops?
    For many we do, or we can easily infer from various distribution analysis methodologies. And your second point is right - our own physiological limits will be severely tested if we pass temperature limits affecting a pollinator species for a major food crop - or indeed that affect any specieas that performs any of the myriad ecological services to which most humans are completely oblivious. This is the basis of my second point at #16,and it is a part of the reason why I try to emphasis that humans are adapted to a certain specific mean global temperature range. Anyone who wants to suggest that we can easily adapt to higher temperature conditions needs to explain exactly how we drag along in that adaptation the rest of the biosphere on which we depend. Humans are not an ecological island, no matter how much a huge swathe of our species imagines otherwise, and omitting such facts from a fantasy future of easy adjustment favours nothing but the imaginations thus assuaged.
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  24. Regarding bees/bats etc. Bees, I know from personal experience, are gloriously happy in a Florida climate. Africanized bees, which migrated north from Brazil, we can presume are pretty healthy in current-tropical climates. Bats do well in Florida, and do well in current-tropical climates. As a general rule, Florida was (and is) a much buggier place than Massachusetts or northern California. There's no doubt a maximum temperature for pollinators, but we're far from it right now in the US. People lived in the South (including Florida) back before air conditioning, though it wasn't a popular choice. If things go as predicted, I expect millions of people will leave Florida, much as millions of people moved to Florida in the previous century. Don't get me wrong, we are definitely rolling the dice on our present course, and they're loaded against us, but there's a difference between godawful costly and end of civilization, never mind end of a species. It's likely that there will be excess deaths, but elsewhere, and our civilization has developed and bumbled along in the face of excess deaths elsewhere for centuries, never mind the awfulness of calling that "civilization". What we call civilization, survived.
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  25. dr2chase. Thanks for that. I have little to no experience with humidity. During extended hot periods here it's quite common to find several dead bees in the garden (when you find the courage and stamina to go outside again).
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  26. Dr2chase. There are two points about your post at #24 that need to be addressed. First, the presence of particular species, in a particular bioclimatic niche, at a particular instant in time, does not actually tell you that they are persistent in that niche over evolutionary spans. To draw that conclusion one requires much more data than simple personal experience. Second (and it's really a reiteration of past posts as well as a segue from the first point), a species does not have to be immediately and profoundly physiologically stressed by a climatic parameter to be compromised by it. Even an apparently 'tolerable' but suboptimal climatic envelope can eventually push a species to extirpation in a particular environment, or, if it is a subtle pressure, to evolution to a more adapted species. This is the whole point of emphasising that humans are adapted in their current form to a mild Holocene climate. We are not adapted to an Eocene maximum, a scenario which would be quite possible if all fossil fuels are burned over the space of a mere few centuries. We just aren't cut our for the addition to mean temperature. Yes, our decendants could move poleward, but life in high latitudes, with seasonalities and with the degraded habitat that we will inevitably leave, will not be nearly as sweet as a palm-shaded beach is today in, say, contemporary Fiji, with a cold beer and an air-conditioned room two minutes walk away. Don't forget that future generations won't have the benefit of the once-off bonanza of energy density that we're chugging down today. Likely, they won't even have access to easily-obtained metals, as we've already exploited the best deposits. They'll be battling an ecosystem that will be massively deforested this century, when the oil peak is long past and wood (rather than the thermodynamically impossible pipedream of widespread renewables) is used in many regions to replace oil (and, in places, coal) for heating and lighting. They'll be battling a resurgence of diseases, including the very recent (by evolutionary standards) HIV which is only scratching its arse at the moment, waiting for a time when a degraded lack of technological capacity to manufacture drugs, combined with a rapidly developing resistance to those that are being used, allows it to sweep through humanity like a dose of Epsom salts. As social and educational sophistication decreases, the safe sex message will diminish, and the 'sleeper' strategy of HIV will ensure that it runs rampantly through many human populations, quite likely to the extent (or greater) that is occurs in places such as Swaziland and Botswana today. And there's TB, and malaria, and a host of enteric viruses, and many cryptic exotics that are simply waiting for the current human monoculture to flip them out of whichever hidden corner in which they're currently percolating. A large proportion of these diseases will all do very well in a warmer world, thank you muchly, not matter how clever the post fossil fuel generations are at shading themselves under trees, in houses, or at the beach. From physiology to ecophysiology, we're not greenhouse animals - no matter how much we can toy with basking in the sun. Heck, as persistence hunters we evolved away most of our fur - and largely during the passage of the last ice age, in fact. We did this because it allowed us to prevent overheating in what was not a greenhouse climate. And yes, it was warm in Africa, but the fact of nakedness still helps to contextualise how we adapted to a thermal upper limit. And granted, we're agricultural these days, more than predatory (although many would disagree). However, if we eschew the advantage of a high protein diet evolution might decide to select for new humans that don't have quite such a high-maintenance brain - and then adjusting to a warm climate becomes more a matter of doing what the environment tells us, and not what our descendants might want to tell it to do. In ten years, or 50 years, or a hundred years, certainly many humans will deal with the heat. Most will, in fact, as long as something else doesn't get them first. But in the longer term, on more evolutionary scales... not so much.
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  27. Bernard J., your musings about future generations and the depleted environment reminded me of "First And Last Men" by Olaf Stapledon. An amazingly far-sighted book which looks at how future species of humans might evolve after us. I suspect that our descendants will not be impressed by the steaming hot planet and lack of resources we are setting up for them. Imagine what we would think of the ancient Greeks if they had done that to us!
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  28. @Bernard. We may not have evolved in a very warm climate, but we seem to have survived for centuries in very warm places (e.g., Africa, Brazil, India, Israel, Iraq), and we survived despite lacking much of the knowledge and technology that we have accumulated since then. I would predict that any parts of the world that end up no warmer in the future than India is now, will have people in them. We may not have evolved in those conditions, but we have demonstrated an ability to survive seemingly indefinitely in those conditions, and in large numbers. This is plain history, not theorizing about properties of human existence. You seem to have a theory that because we did not evolve under these conditions, we will not persist under these conditions. How do you explain all the people living in warm places already? I seem to be completely talking past you, because have I've said all of the above before. The way it looks to me, you have a theory. I have data. My data is inconsistent with your theory. Data wins. How could you disagree with this? Do people not live in India? Is it not much warmer there (and other places) than in most of the US? Is very much of the US predicted to become warmer in the future, than India is now? Same for Europe, Canada, Russia, portions of Africa and South America. And yes, there are predictions for a sufficiently warm world where some places become physiologically uninhabitable. That's not all places, and that's also a very warm world (+12C). And note also (from the article above): "the poles in the Eocene were 30°C warmer than today but the tropics were only a few degrees warmer". The places that are warmest now would not get that much warmer. And I should also admit that when I say "civilization", I have a pretty broad definition. We could have a ten-years-shorter expected lifespan, and it would suck, but it could still be civilization. Less nice than now (sitting in a nice rocking chair, drinking a cold microbrewed beer, tappety-tapping on my laptop, in a climate-controlled room) is pretty damn easy to imagine. And disease -- we survived untreatable disease for millennia. When my great-great-grandfather was my age, he'd been dead thirteen years, from TB probably contracted in the Civil War. Nonetheless, he survived.
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  29. Sapient Fridge @ 27
    Imagine what we would think of the ancient Greeks if they had done that to us!
    IIRC, the Greeks and similar ancient civilisations pretty well deforested large swathes of land around the Mediterranean, in their search for timber to build their navies. Those civilisations destroyed an ecosystem, leaving their descendants a denuded landscape and impoverished soils, not to mention the massive changes this brought to the survival and distribution of endemic species. We also have the example of the inhabitants of Easter Island, who consumed their resources and left nothing for those who followed. Clearly, our species is not good at learning the lessons of history.
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  30. Not to speak for the eloquent Bernard, but it is precisely the unusual stability of the climate since the beginning of the now-ended Holocene that has allowed mankind's techologically-based civilization to thrive. Where shall we assign the arrow with the legend: "Agriculture (and thus civilization) ends"
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  31. If I can buy into the debate, Bernard J is seriously overestimating the pace of evolution. Human ancestors have been upright walkers for five million years but we still experience back problems. We have had children born with large crania for two million years, but mothers still die in child birth. Taking an extreme case, our ancestors have been fully sighted for 400 million years but we still have inverted retina. On a smaller scale, we still have lactose and gluten intolerance in populations that have relied on cows milk and wheat as major sources of nutrition for thousands of years. Evolution is typically a very slow process for any major adaption, or adaption that requires modification of multiple proteins. Adaption rates allowing full adaption with 500 generations require both a simple adaption and very high mortality or infertility rates for those who lack the adaption. When it comes to cold/heat adaption, humans - specifically Homo sapiens where largely confined to tropical Africa where we evolved up to 200 thousand years ago until about 55 thousand years ago. Consequently some human populations have only had about 50 thousand years to evolve cold adaptions. The majority of human populations, however, have always remained in the tropics and have retained the adaption for high heat required. Of those that have evolved for greater cold adaption, even Eskimos have not yet achieved the body proportions that the genuinely cold adapted Neanderthal's had. That shows that human cold adaption is still incomplete and that, for example, physiologically Eskimos are almost as well adapted for the tropics as they are for their current environment. Consequently, given time to acclimatize and general good health, no modern human population would have its survival significantly threatened by merely tropical heat. Against that, if we continue on BAU, even European latitudes will be facing significantly more than tropical heat, taking todays tropical temperatures as a benchmark. However, until temperatures routinely exceeded 40 degrees C with very high humidity, human survival and prospering will not be threatened by mere physiology. In sharp contrast human agricultural productivity will be threatened by even small rises in global temperature. This is due to a number of factors, or which the most important is likely to be a lack of year to year predictability of climate conditions in any location. Coupled to that will be large changes in climate conditions, and slow soil development rates. If, as is likely, southern European and US latitudes become arid, while the Sahara becomes wetter, we will not be able to switch agricultural production from one to the other because it will take generations for suitable soils to develop in the Sahara, or indeed in current tundra. On top of that will be issues of increase virulence of diseases (both human and crop), pest species such as cockroaches, locusts and rats, and the need to find a substitute for fossil fuels to provide the large fertilizer needs of modern agriculture. The biggest threat to human civilization in the coming century will not be from the physiological effects of heat, or even disease, but from a limited ability to feed ourselves.
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  32. Sometimes chance is a bastard. A few days ago I spent about two hours and about two thousand words comprehensively addressing dr2chase's difficulty in understanding the proximal and distal effects that an Eeocene climate would have on the physiology and ecology of humans in a post fossil carbon world. I was more than anguished, then, to be about four words from clicking 'submit' when my laptop shut down automatically, and sent the entire piece to the æther forever. I am in no mood to repeat the hours spent typing, but I will make two points that I had previously elaborated on for a number of paragraphs...
    You seem to have a theory that because we did not evolve under these conditions, we will not persist under these conditions. How do you explain all the people living in warm places already?
    Easily, once the temporary benefit of technology, the brief evolutionary span of its operation, and the confluence of a number of other factors are accounted for. I attempted to detail the overall situation once, however self-education would be perhaps even more valuable for dr2chase, and it would permit me to direct those several hours to other endeavours.
    I seem to be completely talking past you, because have I've said all of the above before. The way it looks to me, you have a theory. I have data. My data is inconsistent with your theory. Data wins. How could you disagree with this?
    I have the advantage of scientific theory. You have incomplete data. Incomplete data rarely wins, especially when it appears to contradict soldily established scientific theory. When you rely on (very) imcomplete data for your conclusion-drawing, any attempt by others to inform you is almost certain to end as an exercise in simply talking past you. Oo, and Tom - don't worry, I am fully cognisant of the pace of evolution! I had elaborated on the significance of this for the likely future of our species in the contexts of both finite energy density availability courtesy of fossil carbon, and of the climate alterations that will result, but despair prevents me from trying again, and anyway it's probably not central to the thread.
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  33. Question: Since we don't really understand why the Eocene Epoch cooled could it be that global warming of the Earth will cool again due to the same factors that made the climate cool after the Eocene?

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