Monday, August 23, 2021

Climate Change: What is the Worst that can Happen?

A Brontotherium, a creature similar to modern rhinos that lived up to some 35 million years ago in a world that was about 10 degrees centigrade hotter than ours. In this scene, we see a grassy plain, but Earth was mostly forested at that time. We may be moving toward similar conditions, although it is not obvious that humans could fare as well as Brontotheria did (image from BBC).


As it should have been predictable, the IPCC 6th assessment report, sank like a stone to the bottom of the memesphere just a few days after it was presented. Put simply, nobody is interested in sacrificing anything to reverse the warming trend and, most likely, nothing will be done. Renewable energy offers hope to mitigate the pressure on climate, but it may well be too late. We may have passed the point of non-return and be in free fall toward an unknown world. 

A disclaimer: I am not saying that nothing can be done anymore. I think we should keep doing what we can, as long as we can. But, at this stage, we can ask the question of "what is the worst thing that can happen?" Models can't help us too much to answer it. Complex systems -- and Earth's climate is one -- tend to be stable, but when they pass tipping points, they change rapidly and unpredictably. So, the best we can do is to imagine scenarios based on what we know, using the past as a guide.

Let's assume that humans keep burning fossil fuels for a few more decades, maybe slowing down a little, but still bent at burning everything burnable, deforesting what is deforestable, and exterminating what is exterminable. As a result, the atmosphere keeps warming, the ocean does that, too. Then, at some point -- bang! -- the concentrations of greenhouse gases shoot up, the system goes kinetic and undergoes a rapid transition to a much hotter world.

The new state could be similar to what the Earth was some 50 million years ago, during the Eocene. At that time, the concentration of CO2 in the atmosphere was of the order of one thousand parts per million (today it is ca. 400) and average surface temperature was about 10-12 degrees C higher than the current one. Note that this is an average: the high latitudes, North and South, where hotter than the low ones, nowhere life would experience temperatures so high that animals would boil alive. So, it was hot, but life thrived and Earth was a luxuriant, forested planet. In principle, humans could live in an Eocene-like climate. The problem is that getting there could be a rough ride, to say the least.

Nobody can say how fast we could get to a new Eocene, but tipping points are fast, so we don't need millions of years. We are thinking, more likely, of thousands of years and significant changes could occur in centuries or even in decades. So, let's try an exercise in looking at the worst-case hypothesis: assuming a warming of 5-10 degrees occurring over a time span of the order of 100-1000 years, what would we expect? It depends not just on temperatures, but on the interplay of several other factors, including mineral depletion, economic and social collapse, and the like. Let me propose a series of scenarios arranged from not so bad to very bad. Remember, these are possibilities, not predictions.

1. Extreme weather events: hurricanes, and the like. These events are spectacular and often described as the main manifestation of climate change. Nevertheless, it is not obvious that a warmer world will show violent atmospheric phenomena. A hurricane is a thermal engine, it transfers heat from a hot area to a cold area. It is more efficient, and hence more powerful, the higher the temperature difference. From what we know, in a warmer world these differences should be lower than they are now, at least horizontally, although vertically it is another matter. Overall, the power of hurricanes would not be necessarily increased. We may have a lot more rain because a hot atmosphere can contain more water, and this is an already detectable trend. Extreme weather events would be mainly local and hardly an existential threat to human civilization. 

2. Fires. Higher temperatures mean higher chances of fire, but the temperature is not the only parameter that enters into play. The trends over the past decades indicate a weak increase in the number of fires in the temperate zone and, of course, fires wreak havoc for those who didn't think too much before building a wooden house in a forest of eucalyptus trees. Nevertheless, as far as we know, fires were less common in the Eocene than they are now, which is what we would expect for a world of tropical forests. Fires should not be a threat for the future, although we may see a temporary rise in their frequency and intensity during the transition period.

3. Heat Waves. There is no doubt that heat waves kill, and that they are becoming more and more frequent. An Eocene-like climate would mean that the people living in what is today the temperate zone would experience summers in the form of a continuous series of extreme heat waves. Paris, for instance, would have a climate similar to the current one in Dubai. It would not be pleasant, but it is also true that people can stay alive in Dubai in Summer using air conditioning and taking other precautions. As long as we maintain a good supply of electricity and water, heat waves don't represent a major threat. Without electricity and abundant water, instead, disaster looms. Heat waves could force a large fraction of the population in the equatorial and temperate zones to move northward or relocate on higher grounds, or, simply, die where they are. The toll of future heat waves is impossible to estimate, but it could mean the death of millions or tens of millions of people, or even more. It may not destroy civilization, but humans would have to move away from the tropical regions of the planet

4. Sea level rise. Here, we face a potential threat that goes from the easily manageable to the existential, depending on how fast the ice sheets melt. The current 3.6 mm/year rate means 3-4 meters of rise in a thousand years. Over such a time span, it would be reasonably possible to adapt the harbor structures and to move them inland as the sea level rise. But if the rate increases, as it is expected to, things get tough. Having to rebuild the whole maritime commercial infrastructure in a few decades would be impossible, to say nothing about the possibility of catastrophic events involving large masses of ice crashing into the sea. If we lose the harbors, we lose the maritime commercial system. Without it, billions of people would starve to death. In the long run, the ice sheets of Greenland and Antarctica will have to melt completely, causing the sea level to rise by about 70 meters, but nobody can say how long that would take. Sea level rise has the potential for substantial disruption of the human civilization, even for its total collapse, but not to cause the extinction of humankind.

5. Agricultural collapseIn principle, climate change, may have disruptive effects on agriculture. Nevertheless, so far warming has not affected agricultural productivity too much. Assuming no major changes in the weather patterns, agriculture can continue producing at the current rates as long it is supplied with 1) fertilizers, 2) pesticides 3) mechanization, 4) irrigation. Take out any one of these 4 factors and the grain fields turn into a desert (genetically modified organisms (GMOs) may not need pesticides, but they have other problems). Keeping this supply needs a lot of energy and that may be a big problem in the future. Photovoltaic-powered artificial food production could come to the rescue, but it is still an experimental technology and it may arrive too late. Then, of course, technology can do little against the disruption of the weather patterns. Imagine that the Indian yearly monsoon were to disappear: most likely, it would be impossible to replace the monsoon rain with artificial irrigation and the result would be hundreds of millions of people starving to death. The lack of food is one of the main genocidal killers in history, directly or indirectly as the result of the epidemics that take advantage of weakened populations. As recently as a century and a half ago, famine directly killed about 30% of the population of Ireland and the toll would have been larger hadn't some of them been able to emigrate. If we extrapolate these numbers to the world today, where there is no possibility to migrate anywhere (despite Elon Musk's efforts to take people to Mars), we are talking about billions of deaths. Famines are among the greatest threats to humankind in the near future, although climate change would be only a co-factor in generating them. Famines may wreck sufficient damage to cause an economic, social, and cultural collapse. 

6. Ecosystem collapse. The history of Earth has seen several cases of ecosystemic collapses involving mass extinctions: the main ones are referred to as "the big five." The largest one took place at the end of the Permian, about 250 million years ago. In that case, the ecosystem recovered from the catastrophe, but it went close to losing all the vertebrates. Most large extinctions are correlated to volcanic emissions of the type called "large igneous provinces" that generate large amounts of greenhouse gases. The result is a warming sufficiently strong to disrupt the ecosystem. The current human-caused emission rate is larger than anything ever experienced by the ecosystem before, but it is unlikely to arrive to levels that could cause a Permian-like disaster. While volcanoes don't care about the biosphere, humans would be wiped out much before they could pump enough CO2 in the atmosphere to cause the death of the biosphere. Nevertheless, a substantial ecosystemic collapse could be caused by factors as the elimination of keystone species (say, bees), erosion, heavy metal pollution, arrest of the thermohaline oceanic currents, and others. The problem is that we have no idea of the time scale involved. Some people are proposing the "near term human extinction" (NTE) taking place in a few decades at most. It is not possible to prove that they are wrong, although most of the people studying the issue tend to think that the time involved should be much longer. The collapse of the ecosystem is a real threat: if it has happened in the past, it could happen again in the future. It may not be definitive and the ecosystem would probably recover as it has done in the past. But, if it happens, it may well be the end of humans as a species (and of many other species). 

7, The unexpected. Many things could cause an abrupt and unexpected change of the state of the system. The stopping of the thermoaline currents is a threat that could wreck disaster on the biosphere, but we don't know exactly what could happen, despite spectacular movies such as "The day after tomorrow"). Then, concentrations of CO2 of the order of 1,000 ppm could turn out to be poisonous for a biosphere that evolved for much lower concentrations. That would lead to a rapid ecosystem collapse. Then, heavy metal pollution could reduce human fertility so much that humans would go extinct in a couple of generations (we are especially sensitive to pollution because we are top predators). In this case, the human perturbation on climate would quickly disappear, although the past effects would still be felt for a long time. Or, we may think of a large scale nuclear war. It would cause a temporary "nuclear winter" generated by the injection of light-reflecting dust into the atmosphere. The cooling would disrupt agriculture and kill off a large fraction of the human population. After a few years, though, warming would return with a vengeance. How about developing an artificial intelligence so smart that it decides that humans are a nuisance and it exterminates them? Maybe it would keep some specimens in a zoo. Or, a silicon-based life would find that the whole biosphere is a nuisance, and proceed to sterilize the planet. In that case, we might be transferred as virtual creatures in a virtual universe created by the AI itself. And that may be exactly what we are! These extreme scenarios are unlikely, but who knows?


So, this is the view from where we stand: the peak of the Seneca Cliff, the curve that describes the rapid phase transitions of complex systems on the basis of the principle that "growth is sluggish, but ruin is rapid." We see a green valley in the distance, but the road down the cliff is so steep and rough that it is hard to say whether we will survive the descent. 

The most worrisome thing is not so much the steep descent in itself, but that most humans not only can't understand it, but they can't even perceive it. Even after the descent has started (and it may well have started already), humans are likely to misunderstand the situation, attribute the change to evil agents (the Greens, the Communists, the Trumpists, or whatever) and react in way that will worsen the situation -- at best with extensive greenwashing, at worst with large scale extermination programs.

So, we may well disappear as a species in a non remote future. But we may also survive the disaster and re-emerge on the other side of the climate transition. For those who make it, the new Eocene might be a good world to live in, warm and luxuriant, with plenty of life. Maybe some of our descendants will use stone-tipped lances to hunt a future equivalent of the ancient Eocene's brontotheria. And, who knows, they might be wiser than we have been. 

Whether humans survive or not, the planetary ecosystem -- Gaia -- will recover nicely from the human perturbation, even though it may take a few million years for it to regain the exquisite complexity of the ecosystem as it was before humans nearly destroyed it. But Gaia is not in a hurry. The Goddess is benevolent and merciful (although sometimes ruthless) and she will live for several hundred million years after that even the existence of humans will have been forgotten.



  1. Six avenues of destruction are outlined. What about two others, straight from the ancient four horsemen of the apocalypse: disease and war? Are humans able to adapt fast enough?

    1. In may view, disease is part of the agricultural collapse. Wars, yes, but they are not a consequence of climate change. If things get really bad, I think people will have neither the resources nor the inclination to make new wars.

    2. Note that I added a 7th point about rather unlikely (perhaps) scenarios. BTW, interesting site, yours!

    3. Non hai esaminato il possibile effetto di un blocco della corrente del golfo, a seguito dello scioglimento dei ghiacci... .

    4. Sorry but war can be a direct consequence of climate change with the collapse of agriculture, famines have always been triggers of war in the past

    5. Thierry, allow me to disagree. Wars are like hurricanes, they need resources to come to life. Without food, people have no force to make war. Not that there won't be wars anymore, but, in the past, periods of decline have been associated with fewer wars.

    6. Luisella, è implicito nel punto dove parlo di collasso agricolo

    7. Hello Professor Bardi,
      As always a thoughtful well formulated essay. Thank you.
      I do have some disagreement on your above comment about war. After collapse, I agree that the survivors won't have time, energy, or resources to wage anything but local short term clashes.
      It is the period leading up to collapse during which I believe we are most at risk. People want to keep what they have, and that includes whatever is their current material standard of living. As the World unravels many will rally behind a leadership that promises them that "they" will protect their way of life from all those external threats. ("the other" that also wants food, resources etc, but must be denied it so whomever the chosen ones are can have it, be it akin to Manifest Destiny, Lebensraum, or a gated community on a national level) A wounded society and culture is similar to a wounded, cornered animal. It will display a ferocity and aggression that would be well outside normal behavior.
      This is why my greatest short term fear is nuclear war with associated nuclear winter....a possible extinction event.
      It may eventually come down to
      1. how much is there?
      2. Who gets what?
      3. How do we retain our Humanity? Will we be able to?

    8. And there also may be increased violence at a local level (crime).

  2. Ya sé que usted ha remarcado que sus puntos eran posibilidades y no predicciones. Pero leyendo, da la sensación que con unas condiciones semejantes al Eoceno, estaríamos en el "paraíso terrenal".

    1. Alas, before going to paradise, you have to die!

  3. A musical moment... ... " Eve of Destruction" is a protest song written by P. F. Sloan in mid-1964

  4. Hello again Ugo. And hello Doc Hall.
    Actually there is a quite strong link between diseases that jump from animals to humans and climate change (ticks, mosquitoes, birds, and now bats.)
    And another rather strong link from climate change to organized violence (the war in Syria, the water wars of the American Wild west, the African genocides,etc.).
    We have added AI and robotics to the stew only recently, but plastics and petroleum products like pesticides didn't exist in enough quantities to matter only a century ago.
    We do things more quickly today. A formula that includes both Moore's and Murphy's laws ...

  5. What is interesting in your description is that most of these factors are linked. Rising sea levels can lead to a salinization of asian deltas, which are major rice production areas. Droughts due to climate change have impacted crops in recent years (in Canada this year). Agriculture as it is done in developed countries depends on fertilization, irrigation, pesticides and plowing, but these are the very factors that have been destroying soil since the beginnings of agriculture. We need to start doing things in a different way, either to dampen the fall, or to become more resilient and adapt more easily to new conditions. In this regard, what do you think of the drawdown project? (

  6. I recently discussed with my son(yes i got too late to vasectomy) maybe the Amazonian Mycelium that is making clouds to bring rain to the woods as a part of the biotic pump are a sign of intelligence. Also the plankton with its snort(DMS) also are able to brightening clouds to protect them from too much sunlight and many other for us not so clear ecological interconnections, underline the Gaia hypothesis. Maybe we live on a planet that exactly knows what is going on and is manipulating us? Like the planet Stanislav Lem described in Solaris? Who knows.

  7. Climate Change has 'crowded out'* an understanding of Energy for the Commence - Globally. A full understanding of Energy meant adding the Right for Humans to Understand What Energy Really Is to An Overhauled, Badly Needed and Now Long Pending Magna Carta**

    The concept for - then - the revolutionary 2008-published mindset “It’s the flows, stupid!” - hase long superseded - the problem is actually much more deeper and universal***.

    Today, we understand that without deforesting Europe and America after the 1500s, early mass British and America coal, Pennsylvania, Texas, Baku and Masjed Soleyman oil - Ghawar's oil wouldn't have come online.

    Unless humans find tomorrow many-folds bigger than Ghawar - talking about more oil, coal and gas is pointless.

    When an oil field peaks, it means it no longer contributes freshly to even its own production - It becomes 100% parasitic to past energies.

    Texas oil has built the Hoover Dam, an industrial base for Ghawar and countless other mega projects - as far as Europe and beyond. Shale oil and gas, in contrast, have destroyed countless roads and urban infrastructures.

    Alaska oil needed massive new infrastructure built before it even started to produce.

    Obsolete, massive steel structures coming from North Sea oil fields into onshore junkyards - are keeping pouring, non-stop. What animates the process is Energy drawn from all over the world.

    This far, all oil fields found and produced after Ghawar were actually a sub product of Ghawar and the earlier energy supplies kept coming into its operation later - including Chinese coal, Iraqi oil, etc.

    If an oil field found today smaller than the original Ghawar, it would be a waste of Energy extracting it.

    "Energy, like time, flows from past to future".

    But who says the Commons around the world are really interested in knowing and understanding all of this jargon - Peak Oil and What Energy Really Is?


    Manufacturing mass Stupidity, burning finite fossil fuels to the last drop in the process, demonstrates that the Manufacturer and the masses are equally stupid - they are humans.

    The masses are slightly more intelligent, though, as they get some priceless fossil fuel supplies, practically for free, in the relationship.

    They survive, re-produce and continue, the Manufacturer and finite fossil fuel reserves diminish over time.


    * 'Crowded Out' is the expression I first read in a comment about Climate Change on

    ** Dmitry Orlov believes Peak Oil is given today the status of Medical Problem, too (link to the interview by JHK - at 45:30).

    *** "No Energy store holds enough Energy to extract, collect and utilise an amount of Energy equal to the total Energy it stores".

  8. Black fuel market in Lebanon - where people push shell-cars, that don't have even engines, to petrol stations, just to get a batch of fuel that they then sell on the black market for profit of few bucks. The narrative that no Peak Oil will never happen because of Price - might have been no more than another intended ambiguity over what Energy really is - all along.

  9. previous papers I have seen indicate some points;
    1. 1000ppm CO2 , plus methane+nitrous oxide + others would give a CO2 equivalent above the level where current modelling indicates equatorial cloud cover would dissipate and something like 18 degrees of global warming results at equilibrium, The equatorial region would be unliveable and also large parts of temperate regions would also be unliveable.
    2. Plant leaves and seeds evolve to become
    more toxic at elevated CO2 levels, I imagine edible crop yield would be severely diminished.
    3. Sea level rise is accelerating, current rate is closer to 5 or 6 mm. another 100mm slr by 2030 and more than a metre by 2050 is quite pausible. SLR on its own could be very disruptive soon.
    4. coextinctions play a dominant role in ecosystem collapse and appear much earlier than human intuition indicates.
    5. putting tipping points together suggests large scale and stable agriculture can't exist, human population must collapse and very fast. the next question is where do all the human bodies go? then, is it plausible that any liferaft population can survive until more stable conditions arise.

  10. Most interesting. Me, à layman, unserstood that some time ago. What could be the human population post this present era?,

  11. Ugo, interesting post I can only concur we will do little and nothing much! One looks wistfully at the Limits To Growth Graphs to see where we are, not predicitive but certainly informative, we are well and truly at a point where the are rising and falling factors, a bit like a small boat in a crossed sea.

    I think Agriculture and the Environmental damage (alteration) is going to be the one. Plant reproduction (seed viability) drops off markedly as temperature rises (There is good analysis of this about the net) and it is a very small range, so heat neuters all biological things excepting a few better adapated. Most of what we rely upon for food is capable of being produced in a temperate range so GAIA very hot is very intemperate indeed. Not sure cacti soup or rodent stew will be too palatable if you like your onions or tomatoes. Our fertility will plummet as well. However the rapidity of all this is the sledgehammer, previous periods took many many millions of years to happen, biological beings had time to adapt or perish. We are so compressing the time it will leave a a very depeleted and sterilised world around, arid in most parts - suffocatingly tropical in others. As for water sure there will be plenty, held in the atmosphere as water vapour or in the oceans with salt but for us not much at all. That seems to be the more likely end excursion. It is going to be a very traumatic journey into the future for us little mammals!

  12. Hot house extinctions, mass & lesser, are the norm as far as extinctions on this planet go.

    There's recent evidence for a 6th mass extinction & it's a hot house mass extinction just like the other 5, including the KT (dinosaurs) - sorry clinging highly emotional Alvarez-asteroid obsessed fanboys.

    Discovery of a new mass extinction
    Press release issued: 17 September 2020

    "The cause was most likely massive volcanic eruptions in the Wrangellia Province of western Canada, where huge volumes of volcanic basalt was poured out and forms much of the western coast of North America.

    “The eruptions peaked in the Carnian,” says Jacopo Dal Corso. “I was studying the geochemical signature of the eruptions a few years ago and identified some massive effects on the atmosphere worldwide. The eruptions were so huge, they pumped vast amounts of greenhouse gases like carbon dioxide, and there were spikes of global warming”.

    The warming was associated with increased rainfall, and this had been detected back in the 1980s by geologists Mike Simms and Alastair Ruffell as a humid episode lasting about 1 million years in all. The climate change caused major biodiversity loss in the ocean and on land, but just after the extinction event new groups took over, forming more modern-like ecosystems. The shifts in climate encouraged growth of plant life, and the expansion of modern conifer forests."

    Sound familiar?

    The only significant difference I can see is previous mass extinctions were not preceded by a rapacious talking ape wiping out tons of habitat before the big hot kicks in. The humans have already done half the work, climate not included. I guess you can say the trigger is different/unique too. That rapacious talking ape digging up all that carbon & burning it as opposed to the standard volcanism (LIP) for all the others. The physics, chemistry & end result are basically the same. I'll wager the humans will be gone before this century is through.

    There's a number of biology professionals, like Bill Rees, who claim habitat loss & other non climate pressures are an existential threat in their own right, yet have gone largely ignored.

    What, Me Worry? Humans Are Blind to Imminent Environmental Collapse
    Accelerating biodiversity loss may turn out to be the sleeper issue of the century.

    "A curious thing about H. sapiens is that we are clever enough to document — in exquisite detail — various trends that portend the collapse of modern civilization, yet not nearly smart enough to extricate ourselves from our self-induced predicament."

    Climate is but one of a number of very dangerous predicaments humans must suffer including how humans behave under pressure when there is little to no hope.