Extinction and Climate

Life on Earth does not enjoy change, and climate change is something it likes least of all. Every aspect of an organism’s life depends on climate, so if that variable changes, everything else changes too – the availability of food and water, the timing of migration or hibernation, even the ability of bodily systems to keep running.

Species can adapt to gradual changes in their environment through evolution, but climate change often moves too quickly for them to do so. It’s not the absolute temperature, then, but the rate of change that matters. Woolly mammoths and saber-toothed tigers thrived during the Ice Ages, but if the world were to shift back to that climate overnight, we would be in trouble.

Put simply, if climate change is large enough, quick enough, and on a global scale, it can be the perfect ingredient for a mass extinction. This is worrying, as we are currently at the crux of a potentially devastating period of global warming, one that we are causing. Will our actions cause a mass extinction a few centuries down the line? We can’t tell the future of evolution, but we can look at the past for reference points.

There have been five major extinction events in the Earth’s history, which biologists refer to as “The Big Five”. The Ordovician-Silurian, Late Devonian, Permian-Triassic, Late Triassic, Cretaceous-Tertiary…they’re a bit of a mouthful, but all five happened before humans were around, and all five are associated with climate change. Let’s look at a few examples.

The most recent extinction event, the Cretaceous-Tertiary (K-T) extinction, is also the most well-known and extensively studied: it’s the event that killed the dinosaurs. Scientists are quite sure that the trigger for this extinction was an asteroid that crashed into the planet, leaving a crater near the present-day Yucatan Peninsula of Mexico. Devastation at the site would have been massive, but it was the indirect, climatic effects of the impact that killed species across the globe. Most prominently, dust and aerosols kicked up by the asteroid became trapped in the atmosphere, blocking and reflecting sunlight. As well as causing a dramatic, short-term cooling, the lack of sunlight reaching the Earth inhibited photosynthesis, so many plant species became extinct. This effect was carried up the food chain, as first herbivorous, then carnivorous, species became extinct. Dinosaurs, the dominant life form during the Cretaceous Period, completely died out, while insects, early mammals, and bird-like reptiles survived, as their small size and scavenging habits made it easier to find food.

However, life on Earth has been through worse than this apocalyptic scenario. The
largest extinction in the Earth’s history, the Permian-Triassic extinction, occurred about 250 million years ago, right before the time of the dinosaurs. Up to 95% of all species on Earth were killed in this event, and life in the oceans was particularly hard-hit. It took 100 million years for the remaining species to recover from this extinction, nicknamed “The Great Dying”, and we are very lucky that life recovered at all.

So what caused the Permian-Triassic extinction? After the discovery of the K-T crater, many scientists assumed that impact events were a prerequisite for extinctions, but that probably isn’t the case. We can’t rule out the possibility that an asteroid aggravated existing conditions at the end of the Permian period. However, over the past few years, scientists have pieced together a plausible explanation for the Great Dying. It points to a trigger that is quite disturbing, given our current situation – global warming from greenhouse gases.

In the late Permian, a huge expanse of active volcanoes existed in what is now Siberia. They covered 4 million square kilometres, which is fifteen times the area of modern-day Britain (White, 2002). Over the years, these volcanoes pumped out massive quantities of carbon dioxide, increasing the average temperature of the planet. However, as the warming continued, a positive feedback kicked in: ice and permafrost melted, releasing methane that was previously safely frozen in. Methane is a far stronger greenhouse gas than carbon dioxide – over 100 years, it traps approximately 21 times more heat per molecule (IPCC AR4). Consequently, the warming became much more severe.

When the planet warms a lot in a relatively short period of time, a particularly nasty condition can develop in the oceans, known as anoxia. Since the polar regions warm more than the equator, the temperature difference between latitudes decreases. As global ocean circulation is driven by this temperature difference, ocean currents weaken significantly and the water becomes relatively stagnant. Without ocean turnover, oxygen doesn’t get mixed in – and it doesn’t help that warmer water can hold less oxygen to begin with. As a result of this oxygen depletion, bacteria in the ocean begins to produce hydrogen sulfide (H2S). That’s what makes rotten eggs smell bad, and it’s actually poisonous in large enough quantities. So if an organism wasn’t killed off by abrupt global warming, and was able to survive without much oxygen in the ocean (or didn’t live in the ocean at all), it would probably soon be poisoned by the hydrogen sulfide being formed in the oceans and eventually released into the atmosphere.

The Permian-Triassic extinction wasn’t the only time anoxia developed. It may have been a factor in the Late Triassic extinction, as well as smaller extinctions between the Big Five. Overall, it’s one reason why a warm planet tends to be less favourable to life than a cold one, as a 2008 study in the UK showed. The researchers examined 520 million years of data on fossils and temperature reconstructions, which encompasses almost the entire history of multicellular life on Earth. They found that high global temperatures were correlated with low levels of biodiversity (the number of species on Earth) and high levels of extinction, while cooler periods enjoyed high biodiversity and low extinction.

Our current situation is looking worse by the minute. Not only is the climate changing, but it’s changing in the direction which could be the least favourable to life. We don’t have volcanic activity anywhere near the scale of the Siberian Traps, but we have a source of carbon dioxide that could be just as bad: ourselves. And worst of all, we could prevent much of the coming damage if we wanted to, but political will is disturbingly low.

How bad will it get? Only time, and our decisions, will tell. A significant number of the world’s species will probably become extinct. It’s conceivable that we could cause anoxia in the oceans, if we are both irresponsible and unlucky. It wouldn’t be too hard to melt most of the world’s ice, committing ourselves to an eventual sea level rise in the tens of metres. These long-range consequences would take centuries to develop, so none of us has to worry about experiencing them. Instead, they would fall to those who come after us, who would have had no part in causing – and failing to solve – the problem.

References:

Mayhew et al (2008). A long-term association between global temperature and biodiversity, origination and extinction in the fossil record. Proceedings of the Royal Society: Biological Sciences, 275: 47-53. Read online

Twitchett (2006). The paleoclimatology, paleoecology, and paleoenvironmental analysis of mass extinction events. Paleogeography, Paleoclimatology, Paleoecology, 234(2-4): 190-213. Read online

White (2002). Earth’s biggest “whodunnit”: unravelling the clues in the case of the end-Permian mass extinction. Philosophical Transactions of the Royal Society: Mathematical, Physical, & Engineering Sciences, 360: 2963-2985. Read online

Benton and Twitchett (2003). How to kill (almost) all life: the end-Permian extinction event. Trends in Ecology & Evolution, 18(7): 358-365. Read online

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Deniers?

I really enjoyed New Scientist’s Special Report: Living in Denial. What a fascinating phenomenon, and a fascinating batch of articles exploring it.

The denial of science is a growing problem. It’s not restricted to a particular ideology – while denying the harmful effects of smoking or the existence of climate change is typically a position of the far right, vaccine denial and H1N1 conspiracy theories are largely restricted to the left.

It occurs even among the well-educated, or among youth who are still immersed in up-to-date curricula. For example, this year at the university, a student group put up signs saying “Don’t get the swine flu shot – it contains mercury!” The chemistry students got mad, and said that labelling thimerosal as toxic mercury was comparable to saying “Don’t eat table salt, it contains chlorine gas!”

As Michael Shermer’s article explains, the defining mark of science denial is a refusal to change one’s mind based on evidence. This is easy to identify for something like Holocaust denial, where evidence is abundant in the public sphere.

It gets a little harder for more technical issues like climate change or vaccines. Scientific opinion is overwhelmingly on one “side”, but the average person does not know or understand the evidence to support this consensus. An article about the thermodynamics of the stratosphere won’t sell a lot of papers. Most people unconsciously follow the credibility spectrum and trust what their doctor or NASA scientists say.

However, some don’t realize that scientific credibility is not the same as an appeal to authority, and so express contrarian opinions. Vaccines cause autism. Global warming is nonexistent/natural/inconsequential. The way that the Twin Towers fell proves that it was orchestrated by the US government.

There are two groups of contrarians: the skeptics, and the deniers. The skeptics are the ones who will change their minds based on evidence – they just haven’t encountered that evidence yet. My favourite example of this is from the Friends episode when Phoebe declares she doesn’t believe in evolution. When Ross starts talking to her about fossils, she says, “Oh. I didn’t know there was actually evidence.”

It’s amazing how many insights you can get out of a supposedly “fluffy” sitcom. I could write an entire essay analyzing that clip…..

I have met dozens of very reasonable people who doubt climate change because they don’t know about the evidence for it. People my age throw around the phrase “it’s a natural cycle” a lot, until I explain that the climate doesn’t act like a pendulum. It doesn’t have to compensate for past periods of warming or cooling – it simply responds to forcings. If the forcing is cyclical, then the climate will be cyclical, but some forcings are a different shape altogether. Similarly, I know a teacher who previously thought that natural causation of the current warming was a legitimate scientific theory, due to a presentation from a teacher’s conference….until I did a bit of probing and discovered that this presentation was given by Tim Ball.

These people are very reasonable. They are willing to change their minds based on evidence. They’ve just been unlucky enough to be misinformed by our flawed system of science journalism.

Then there are the deniers. They call themselves skeptics, but they will not change their minds, no matter what evidence you give them. They either move the goalposts, change the subject, or continue to repeat the same claim even after you have rebutted it patiently multiple times. Go check out some YouTube comments to see what I’m talking about.

Often their ideology or worldview is extreme in some way. For many members of the far right, any problem that would be solved by the government (think cap-and-trade or smoking legislation) will be rejected out of hand. On the far left, anything that would benefit corporations (usually vaccines or traditional medicine) will face a similar reaction. As Michael Specter says, “We hate Big Pharma. We run away from Big Pharma….and leap right into the arms of Big Placebo.”

This phenomenon suggests that science communication is not the answer – for deniers. I learned long ago that trying to change the minds of deniers is a complete waste of time. However, I still feel that science communication and the rebuttal of common misconceptions is absolutely vital. The true skeptics need access to the evidence they are lacking, so that they will be more informed, and our population will move farther towards solving the many science-related problems we face.

These skeptics deserve our time, our efforts, and our respect. They are the target audience of my blog, even if my most active commenters and supporters are a different group altogether. The reason that any of us here do all this work in communication, I believe, is for the true skeptics.

Michael Fitzpatrick argues that we shouldn’t use the label “deniers” at all. I wouldn’t want to alienate the true skeptics by coming across as someone who insults others. However, I think that calling deniers “skeptics” is unfair to the skeptics. They are two completely different groups that we must distinguish between. Skepticism is a worthy quality in science, and giving the complimentary title of “skeptic” to someone who doesn’t deserve it is unfair to those who do. We need to cater to the people who are willing to learn and who don’t want to waste our time. Science communication shouldn’t have to be like No Child Left Behind.

Michael Shermer’s second article, similarly, says that we should participate in debates with deniers and give them a chance to be heard. The truth will prevail, he argues, even if the deniers refuse to give in. I would agree with this position if it were a matter of opinion or policy, which is wholly democratic. Yet science is completely different. Science isn’t about free speech and giving equal time for all views. It is about giving time to those who have the most accurate analyses and robust conclusions. In science, you shut up and listen until your ideas are strongly supported by evidence. Then you publish.

When papers skeptical of climate change get published (all three per year!), such debates are worthy. The authors passed the test of peer-review, and even if their papers are obviously sub-par and are soon to be retracted, they deserve some debate and discussion. Let’s debate contrarian science when it is actually science – when it is actually published.

By paying close attention to and publicly debating with the authors of blog science, however, we are further confusing the public’s already skewed image of science. “It doesn’t matter whether or not you publish,” we seem to be telling them, “it’s all about free speech.” The scientific process has rules, and if deniers can’t pass the necessary, but not sufficient, condition of peer-review, their work doesn’t deserve to be treated as scientific research, and we shouldn’t give them our attention.

Let’s ignore the people who aren’t worth our time, because we have limited time, and there are people out there who deserve every minute of it.

Climate Change and Evolution

Many advocates of anthropogenic climate change are also advocates of the theory of evolution. The two are often used in analogy in many different ways. In particular, skeptics of the two theories are often alleged to be either the same people or using the same tactics to spread public confusion.

I am not strongly religious, and I fully accept evolution. I understand that some others do not as it conflicts with their spiritual beliefs. I understand that alternative theories have failed to stand up to scientific scrutiny in the peer-reviewed literature. It is my opinion that these theories of creation or intelligent design should remain religious beliefs, and not attempt to be passed as objective science.

But I really don’t mind if people out there don’t believe in evolution. I couldn’t care less.

My feelings are exactly the opposite on anthropogenic global climate change. Why?

The difference between the evolution debate and the climate change debate is that the latter has consequences for the real world. Endless public debating and alternative theories about climate change could easily spread confusion and delay action to mitigate the threat. Indirectly, public debating on climate change, rather than leaving the debate to the scientists and taking action based on their conclusions, poses a threat to our future and our way of life.

Debating on evolution, in contrast, isn’t like that. At worst, it could slow down scientific progress in the area of biology. It could offend people. But could it wipe out our civilization? Of course not. Could climate change? Even the most skeptical person has to admit that it is a possibility.