Bardi: What is the Worst that can Happen?

Climate Change: What is the Worst that can Happen? Ugo Bardi. Aug. 22, 2021.

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 that 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 and we should try to do our best to move in the right direction, 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, deforest what is deforestable, and exterminate 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. 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 6-10 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, so the power of hurricanes would be reduced, not enhanced. 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 eucalypti. 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 survive 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, 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. 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 with the sea level rise. But 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 collapse. In 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 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), 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 sufficient 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. Unlike volcanoes, which 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 will 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. As an example, 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 we are a nuisance and it exterminates humankind? 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.