How Likely is Total Climate Doom?

Nowadays there is a certain type of extreme pessimist that we might call a climate doomer. A climate doomer may believe that global warming will cause the end of human civilization, or perhaps even human extinction. A favorite blog of climate doomers is the blog Nature Bats Last. In this blog post on that site, Guy McPherson compiles an alarming set of statements and links to support the position that global warming will cause the collapse of civilization and perhaps even human extinction.

But how likely is the "total climate doom" scenario, meaning human extinction caused by climate change? Let's try to calculate the odds of it, using a simplified type of probability analysis.

Factor #1: Fossil Fuel Resource Production

Currently the amount of carbon dioxide in the atmosphere is is about 400 parts per million. How high will this level be at the end of the century? Estimates vary widely. A recent IPCC report includes the following graph, which shows possibilities ranging from about 460 to 1000. Three out of six scenarios shown on the graph predict a lower carbon dioxide level, of only about 460 to 540.

IPCC scenarios

It is very hard to predict how much carbon dioxide will be in the atmosphere at the end of the century, because the matter depends on how high the production rate will be for various types of fossil fuels (the higher that production, the greater the amount of carbon dioxide will end up in the atmosphere). This issue is much more complicated than one might think from statements such as “We have enough coal in the ground to fry the planet.” Such a statement may be as misleading as the statement that there's enough gold in the ocean's seawater to make every person a millionaire (a statement that doesn't mean much because it's too difficult to extract such a resource).

For each fossil fuel resource there is an “availability pyramid” like the pyramid shown below. Most of the resources are at the bottom of the pyramid, and such resources are much harder to extract than the easy-to-extract “low hanging fruit” at the top of the pyramid. At some position in the pyramid it becomes no longer economically viable to extract the resource, but we don't know where that point is. It is therefore very difficult to predict fossil fuel resource production in the remainder of this century. Peak Coal and Peak Oil may put a brake on such production.

There are quite a few experts who predict that the production of coal and oil will plunge later in this century, as we work our way down the coal and oil availability pyramids, and start trying to extract resources that are more and more difficult to extract. For example, David Rutledge of Cal Tech predicts that 90% of the world's coal production will occur by 2070, which means a plunge of coal production later in this century. He suggests that this will mean that carbon dioxide levels will not exceed about 500 parts per million by the end of the century.

For the sake of this simplified probability analysis, let us assume that there is a 50% chance that fossil fuel production will not decline very much because of availability and extraction difficulty reasons (which we can call Condition 1A), and a 50% chance that such production will indeed plunge in this century because of availability and extraction difficulty reasons (which we can call Condition 1B). The first of these two conditions is necessary for the worst-case-scenario of a climate doom bad enough to cause human extinction.

Factor #2: Clean Energy, Conservation and Legislative Measures

Another factor that will determine how much carbon dioxide is in the atmosphere at the end of the century is how much effort humans make to restrict their use of greenhouse gases, and prevent global warming. If we keep on with “business as usual” without doing much to fight global warming, that will make a worst case scenario more likely. But if we conserve and cooperate, build lots of clean energy, eat less meat, and follow international protocols such as successors to the Kyoto Protocol, that will make a worst case scenario less likely.

For the sake of this simplified probability analysis, let us assume that there is a 50% chance that humans will not do very much to restrict global warming through such measures (which we can call Condition 2A), and a 50% chance that humanity will get very serious about reducing global warming through such measures (which we can call Condition 2B). The first of these two conditions is necessary for the worst-case-scenario of a climate doom bad enough to cause human extinction.

If global warming gets much worse during this century, this should increase the chance of people being alarmed enough to start taking the necessary measures to fight global warming through measures such as conservation. So we should not rate the likelihood of Condition 2A as being more than 50%.

Factor #3: Climate Sensitivity

Another factor that will determine how bad global warming will get is what is called climate sensitivity. Climate sensitivity means how much the earth's temperature will go up for after a given rise in carbon dioxide in the atmosphere. Scientists debate how much the temperature will rise if the carbon dioxide in the atmosphere doubles from its current level of 400 parts per million, to become as high as 800 parts per million. A post on RealClimate.org says, “The ‘meta-uncertainty’ across the methods remains stubbornly high, with support for both relatively low numbers around 2ºC and higher ones around 4ºC, so that is likely to remain the consensus range.” The more dire projections of future global warming assume a high climate sensitivity.

For the sake of this simplified probability analysis, let us assume that there is a 50% chance that climate sensitivity is high (which we can call Condition 3A), and a 50% chance that climate sensitivity is relatively low (which we can call Condition 3B). The first of these two conditions is necessary for the worst-case-scenario of a climate doom bad enough to cause human extinction.

Factor #4: Amplifying Feedback Mechanisms

If conditions 1A, 2A, and 3A mentioned above all occur, this will be enough to cause horrifying trouble for the human race, resulting in the ruin of many coastal cities, the loss of countless species, a huge increase in wildfires, and a huge increase in desertification. But by themselves those conditions would not be enough to cause human extinction. The human race could always abandon all areas around the middle of our planet, and move entirely to regions such as Canada and Russia (or, if things got really hot, to the continent of Antarctica after its ice melted). In order for you to have human extinction by global warming, you would also need to have feedback mechanisms that amplify global warming once its gets going very strong.

Pessimists have raised concern that such amplifying feedback mechanisms may exist. One of the most frightening possibilities is the melting of methane hydrates, natural sources of methane that exist in places such as Siberia and Antarctica. Methane is a greenhouse gas 20 times more potent than carbon dioxide. So if man-made global warming starts melting frozen methane hydrates, that might cause the release of more and more methane into the atmosphere. That in turn could cause more and more methane hydrates to melt. It could possibly be a deadly feedback mechanism that could amplify global warming.

Experts disagree over how much we should be worried about the possibility of such feedback mechanisms. Some say it's a huge concern, while other say the risk is small.

For the sake of this simplified probability analysis, let us assume that there is a 50% chance that planetary feedback mechanisms will one day start amplifying global warming (which we can call Condition 4A), and a 50% chance that such feedback mechanisms will not be a very big factor (which we can call Condition 4B). The first of these two conditions is necessary for the worst-case-scenario of a climate apocalypse bad enough to cause human extinction.

Factor #5: Geoengineering

There is one last factor we must consider: the possibility of geoengineering. When people use the term geoengineering when talking about global warming, they are talking about man-made measures designed to directly reduce the effects of global warming. Various techniques have been proposed. One technique would place on the oceans many specially designed ships that would create mist out of sea water, a salty mist that would rise in the atmosphere and increase the amount of sunlight reflected by the atmosphere (thereby lowering temperatures).

Opinions vary over whether geoengineering techniques would work to effectively fight global warming. For the sake of this simplified probability analysis, let us assume that there is a 50% chance that geoengineering techniques would not effectively reduce global warming (which we can call Condition 5A), and a 50% chance that such techniques would be effective (which we can call Condition 5B). The first of these two conditions is necessary for the worst-case-scenario of a climate apocalypse bad enough to cause human extinction. No such climate doom would occur if we had an effective way to prevent it with geoengineering.

So What is the Chance of Total Climate Doom?

So given all these considerations, what is the chance of global warming causing the extinction of the entire human species? In each of the five issues I have discussed, there is a particular condition that must occur in order for total climate doom to happen. Let us assume that the probability of each of these conditions is independent of all of the others. If that is true, then to calculate the combined probability of each condition occurring we multiply together the individual probabilities. This gives us the following formula:

Probability of total climate doom =
probability of Condition 1A (undiminished fossil fuel resource production) multiplied by
probability of Condition 2A (“business as usual” without huge efforts at conservation and clean energy) multiplied by
probability of Condition 3A (high climate sensitivity) multiplied by
probability of Condition 4A (amplifying feedback mechanisms) multiplied by
probability of Condition 5A (no effective geoengineering)

Substituting the probabilities I have listed, this gives us a probability of total climate doom equal to 50% multiplied by 50% multiplied by 50% multiplied by 50% multiplied by 50%. So according to this simplified analysis, the probability of total climate doom (meaning complete human extinction because of global warming) is roughly 1 chance in 32, or about 3 percent.

It would seem, therefore, that the chance of complete human extinction by global warming is quite low, but still large enough to be worth worrying about.

But this does not mean that we can be complacent, or that we should lessen efforts to fight global warming. For one thing, a 3 percent risk must be considered a very substantial risk when one is talking about something such as total human extinction. For another thing, there is a possibility not quite as catastrophic as total climate doom, a possibility that we might call decimation by global warming. As decimation means literally to destroy a tenth, we may define decimation by global warming as the possibility that something like a tenth of the human species will be wiped out by global warming. That possibility is a lot more likely than total climate doom, and might require only three or four of the five conditions necessary for total climate doom. The math would get a little complicated as to how to calculate such a likelihood, but I think the chance is significantly higher than 3 percent. Such an outcome would be far worse than any world war the world has seen, and its avoidance is something all of us have a moral duty to prevent.

Speaking in purely practical terms, I think that to argue for “total climate doom” is perhaps not very helpful in the fight against global warming. If you persuade a man that global warming will cause great trouble for mankind, many deaths, and a risk of extinction, that person may well change his actions to help fight the problem. But if you persuade a man that the whole human race is going to become extinct from global warming, then the person may just tend to think that action is futile, and that it makes no difference how he acts.

Are You a Mere Pawn of Physical Laws?

On the LiveScience.com site the other day there was an interview with Columbia University physicist Brian Greene. For a long time Greene has been one of the main proponents of string theory, a theory which has failed to gain any observational support. In a 2003 interview Greene candidly says, “I've spent something like 17 years working on a theory for which there is essentially no direct experimental support.” By now I suppose that figure should be revised to be 28 years, as there is still no evidence for string theory. In fact, most forms of string theory are based upon another theory (supersymmetry) that has been endangered by recent observations.

You might think such a shortfall would produce a certain intellectual humility, some thoughts along the lines of: what do I really know? But that doesn't seem to have happened in the case of Professor Greene, as he feels confident enough to tell us that we don't really have such a thing as free will.

The reason given by Greene in this interview is that everything has to have a “fundamental microphysical underpinning.” Greene says, “When I move my teapot, that sensation is absolutely real,. But that's all it is. It's a sensation."

This is not a coherent argument against free will. First, we know of incredibly important phenomena that do not occur for microphysical reasons, including the effects of gravitation (gravitation has no detectable effects on any microscopic or subatomic scale, nor any known microphysical cause). Secondly, it is entirely possible that consciousness and free will might have a microphysical underpinning.

In the case of a common-sense thing such as free will, the burden of proof is on the skeptic. Since almost all of us intuitively feel that we do have free will, if you're going to try to overturn that common-sense assumption, you'd better have a pretty good argument, rather than just some lazy phraseology.

Earlier this year Greene gave an interview in which he stated this argument against free will:

But as a snapshot, if you look at the equations that we have today, there does not seem to be a place anywhere in those equations where you say, oh, OK, and here is where human free will comes in to how things are going to evolve. Right? There’s no term in the equations where that happens.

This seemed to produce a laugh from the interviewer, as well it should have. For a physicist to argue that free will doesn't exist because he doesn't see it in his equations is like a biologist arguing that love doesn't exist because he doesn't see it in his microscope.

The equations of physicists describe certain relations between quantifiable aspects of our universe, involving matter, energy and forces in our universe. There is not the slightest reason to think that a physics equation would or could ever refer to some unquantifiable thing such as free will.

Physics isn't just equations, but also experiments. When we look at some of the more interesting physics experiments, we actually see things that mesh well with the concept of free will. In the famous double-slit experiments (well described in this video), particles behave differently depending on whether or not they are observed. In one of these experiments, when electrons are being observed, they act like particles, but when they are not being observed they act like waves. Although the experiment doesn't prove anything directly about free will, it suggests that the behavior of particles is directly affected by human consciousness, rather than the deterministic idea that we are merely “particle pawns” riding in the back seat with physics always being in the driver seat.

The experiments described here indicate that human thought has the ability to change the interference patterns produced in the double slit experiment, which again suggests that the human mind can causally affect microphysical phenomena, rather than the idea that our thoughts or choices are merely things that are passive products of such phenomena.

When it comes to free will, Greene's attitude seems to be: I can't believe in that, because I don't see it in my equations. But Greene throws away such a rule when it comes to things infinitely harder to believe in than free will. For Greene has written a book called The Hidden Reality talking enthusiastically at great length about claims such as parallel universes and vast collections of other universes. Of course, there is no verified equation that gives support for any such ideas. Equations deal with quantifiable physical things in our universe, so an equation could never support a conclusion about a parallel universe or another universe.

Why the double standard? I think it may come down to dollars. Speculating about parallel universes and other universes is a lucrative little cottage industry for many a modern physicist, a nice safe way to boost your salary. All a modern physicist needs to do is write a book on the topic, and he runs no risk at all that anyone will prove him wrong (since no could ever prove or disprove these ridiculously speculative theories). So while Greene gets all minimalist and skeptical and parsimonious when it comes to free will (denying it on the basis that it's not in the equations), he goes a million miles in the completely opposite direction when it comes to parallel universes and other universes, setting forth on endless ultra-extravagant speculative flights of fancy, much of it fit for pulp science fiction magazines. Very inconsistent, but at least it rakes in the royalties.

In this interview Greene ties together his rationale for rejecting free will with his affection for parallel universes. Greene says:

"We do not see free will in the equations: you and I are just particles governed by particular laws. Every individual, faced with five choices, would make all five -- one per universe. And all of the choices would be as real as the others."

Besides being morally poisonous (a perfect prescription for moral indifference), this seems like one of the looniest statements I have ever heard a physicist make. As I discuss here, there is no evidence or good argument to support such fatuous thinking (just as there is no evidence to support the string theory that Mr. Greene has been selling for so long).

So are you a mere pawn of physical laws? No, you are not. You have free will that is as real as your own consciousness. If you commit a moral error, you cannot use the excuse of “the physics made me do it.”

The Silence of the Blissful: A Science Fiction Story

Jeff Hunt was a blogger with a strong social conscience, and in the year 2040 he found plenty of things to complain about. Jeff denounced the ever-growing levels of wealth inequality, and he complained that the middle class was starting to become an endangered species. Jeff castigated politicians for seemingly being in the pocket of the richest 1 percent. Shining a light on dubious projects of the Government, Jeff showed how many projects were pork-barrel boondoggles designed mainly to line the pockets of corporations. When Jeff found cases of government duplicity and deception, he exposed them to illuminating scrutiny.

The Government noticed the growing readership of Jeff's blog, and one day Jeff received a phone call from a government official.

“We've noticed your complaints, and we want to show you that we listen to our critics,” said the official. “Why don't you come into my office, and we'll discuss your grievances.”

Jeff was worried. He had heard vague rumors of how the Government had “got to” some of its critics. Jeff nervously walked into the government office and met the government official who had agreed to meet with him.

Jeff was rather surprised by how long a time he was allowed to talk, and he also found it surprising that the government official did not dispute anything he said. Jeff talked on and on for twenty minutes about all the government corruption, waste, and folly he had written about in his blog. The government official took notes as Jeff spoke.

“We thank you for the input,” said the bureaucrat. “I am going to file a full report on your complaints, and I'm sure the report will attract great attention by the relevant government officials. But since I'm doing this favor for you, it is only fair that you do a little favor for me.”

Uh-oh, thought Jeff; what are they going to ask for?

“We are testing an important new medicine,” said the bureaucrat, “and we need you to participate in our test. Please take these three pills, and try them, one every two hours. We'll be in touch to ask about your reaction.”

The bureaucrat gave Jeff the pills. One was red; the other yellow; and the other blue. Jeff went back to his apartment. The bureaucrat threw away his notes.

Back in his apartment, Jeff looked at the pills with a worried face. He thought to himself: could these pills have some kind of poison?

He decided to bite off just a tiny piece of the red pill, just to be safe. Far from causing any discomfort, the pill produced the opposite effect. Jeff felt wonderful. He swallowed the rest of the pill.

For the next two hours Jeff felt better than he had ever felt before. It seemed as if every piece of flesh in his body was pulsating with the most wonderful pulsation ever pulsated. It was as if every part of his flesh was a tongue, a tongue that was tasting some food from the tables of paradise, a food a hundred times more delicious than the most delicious food a human has ever prepared. It was a sensation far, far better than sex.

Finally the effect wore off. Without much hesitation, Jeff swallowed the yellow pill. The pill had an amazing effect. Jeff could close his eyes, and he would see the most glorious dreamlike visions. He saw visions of shining glass castles floating in the clouds. He saw visions of a hundred gorgeous naked women dancing on a vast green meadow. He saw visions of strange extraterrestrial planets where flying vehicles silently drifted through urban canyons stretching miles high up into the air.

After two hours, the effect of the yellow pill wore off. Jeff then took the blue pill, asking himself: what delight will this one produce?

He soon found out. The pill made him laugh uncontrollably at everything. He looked at a little crack in his wall, and spent twenty minutes rolling on the floor, laughing uncontrollably. The little crack seemed the funniest joke ever told in the history of the world. Then Jeff picked up a spoon and looked at that. He spent thirty minutes laughing hysterically at the spoon, wondering why he had never previously noticed how infinitely funny spoons are.

Finally the effect wore off. Jeff went to sleep, wondering what kind of weird medicine the government was testing.

When Jeff woke up the next morning, he was filled with a tremendous physical, mental, and spiritual craving. Jeff knew exactly what it was: he had to have more of those pills. He thought to himself: I'll have to go back to that bureaucrat, and get more of those pills. But then he realized: it was Saturday, and the government office would be closed.

Jeff shuddered. No, no, no, no, Jeff thought, I must, I must, I must have more of those pills! I need them now, now, now, now!

For an hour Jeff was in agony. He thought of not having the pills for the rest of the day, and the idea seemed like the most impossible impossibility ever conceived. Jeff asked himself: what, what, what can I do to get more of those pills – I MUST have them!

Then Jeff got a text message on his wrist smartphone. The message said: Check your mail box.

Jeff bolted down the stairways to the lobby of his apartment, and opened his mailbox. There in the box was a little envelope. Excitedly, Jeff opened it. Inside the envelope were 6 pills: two red, two yellow, and two blue.

Jeff laughed ecstatically. For now, his problem was over. He went back upstairs and enjoyed the pills again.

From then on Jeff found a little envelope in his mailbox every day except Sunday. On weekdays each envelope would have three pills, and on Saturday the envelope would have 6 pills. Several times there was a little message in the envelopes. The message said:

Keep quiet, or we'll take you off the mailing list.

Jeff stopped writing on his blog. He knew that his silence was the price of getting the pills. But Jeff didn't care much any more about social issues, and he had lost interest in being a government critic. All he cared about now was getting and enjoying what he absolutely had to have every single day: the red, blue, and yellow pills.

Jeff was like many thousands of other government critics who had been quietly silenced by the little pills. As someone in the Government had once said with a chuckle: no rebellion or political movement ever got started by a drug addict.

The Faint Young Sun Paradox: An Unsolved Mystery

The origin of life seems to require liquid water. Geological evidence indicates that our planet was warm enough for liquid water to have existed about 3.5 billion years ago, when the first earthly life appeared. But models of solar evolution lead scientists to conclude that the sun gave off much less heat billions of years ago. Judging only from the sun's evolution, our planet should have been completely frozen three billion years ago. This discrepancy is known as the faint young sun paradox.

Below is a diagram from a scientific paper by Shani and Shtanov discussing the faint young sun paradox. As you can see from the diagram, if we assume (for the sake of simplicity) that our planet has had its current atmosphere for the past 3 billion years, then our entire planet should have been frozen until about 1.7 billion years ago.

Scientists have advanced some explanations for the faint young sun paradox, but none of them is problem-free. One explanation is that billions of years ago our planet's atmosphere was vastly different. It could have been that billions of years ago our atmosphere had vastly more carbon dioxide and methane. That would have produced a greenhouse effect many times greater than the greenhouse effect currently produced by man-made pollutants.

But there are some problems with this theory. There would have needed to be almost ridiculous amounts of carbon dioxide and methane in the atmosphere for the greenhouse effect to have been sufficient to explain the paradox. For example, in this link there's a discussion of some scientists hinting that they have solved the faint young sun paradox through a greenhouse gas explanation. But they imagine carbon dioxide levels of 20,000 parts per million – fifty times greater than today's level. Why are such high levels of greenhouse gases implausible? A good explanation is given by this scientific paper by Shani and Shtanov:

While CO₂ [carbon dioxide] can be removed from the atmosphere by bacteria and plants during photosynthesis and also by the weathering of rock, the enormous concentrations referred to earlier seem difficult to account for. Indeed, large amounts of CO₂ in the early atmosphere would have led to the formation of the iron carbonate based compound siderite (FeCO₃). However, analysis of billion year old paleosols challenges this picture by finding no FeCO₃. Found instead are iron silicates which support a much more moderate presence of CO₂ in the early atmosphere. Moreover, it would be difficult to make CO₂ disappear almost entirely from the Earth’s atmosphere since much of it, after reacting with rocks and being used by shell-forming organisms to form CaCO₃ shells, gets deposited on the ocean floor and makes its way back into the atmosphere via volcanic activity and plate tectonics . The presence of other greenhouse gases is equally problematic.

The paper makes the point that if you had once had fantastically high levels of carbon dioxide (CO₂) in the atmosphere, and that had slowly disappeared, much of that carbon dioxide would have been stored in what are called carbon dioxide “sinks.” But over the eons the carbon dioxide in those sinks would have been slowly re-released by geological processes – which would have left us with more carbon dioxide in the atmosphere than we have today.

What solution do Shani and Shtanov suggest for the faint young sun paradox? They suggest a varying gravitational constant. The gravitational constant is the fundamental constant that indicates the strength of gravitation throughout the universe. It is one of several fundamental constants that are crucially important in determining the behavior of the sun. The authors suggest that if the gravitational constant had varied by 2 percent over the past few billion years, that could explain the faint young sun paradox.

This explanation can be called something of a “Hail Mary pass.” Scientists don't quite have a rule of “if all else fails, suggest the laws of nature have changed,” but assumptions about changing laws of nature or changing physical constants are generally regarded as a kind of last resort. This paper by Pitjeva and Pitjev claims to set a limit on changes in the gravitational constant. The paper (based on spacecraft observations) concludes that the gravitational constant changes by less than 1 part in 20,000,000,000,000 per year. This conclusion is hugely inconsistent with the hypothesis of Shani and Shtanov that the faint sun paradox can be explained by assuming a 2 percent variation of the gravitational constant. If Pitjeva and Pitjev are correct, the gravitational constant could not have varied by more than 1 part in 10000 during the past five billion years, a limit which rules out a 2 parts in 100 (2 percent) variation as imagined by Shani and Shtanov.

That apparently shoots down a varying gravitational constant as an explanation for the faint young sun paradox. But what about other fundamental physical constants that the sun's behavior depends on, such as the fine-structure constant? That's not an area scientists prefer to be fiddling with, for two reasons. First, it has already been concluded that the sun is extremely sensitive to changes in the fine-structure constant, and that if it were only the tiniest bit different, the sun would be some other type of star such as a red dwarf or a blue giant. For example, this paper by a physicist finds that changing the fine-structure constant by 2 parts in 1000 would cause the earth to freeze, and changing the fine-structure constant the other way by only a few percent would cause the earth's water to boil. Given this extreme fine-tuning of the fine-structure constant, do we really want to imagine some other fine-tuning, some just-right slow change in the fine structure constant to resolve the faint young sun paradox? Also, a study based on earthly isotopes indicates that the fine-structure constant is totally invariant over the eons, varying by less than 1 part in 10,000,000,000,000,000 per year.

So where does that leave us in regard to the faint young sun paradox? We are left with an unsolved mystery. Somehow our planet was warm billions of years ago, but we really don't know why it wasn't completely frozen. Considering the matter, we should be humbled, and remember how fragmentary and incomplete our knowledge of nature is.