Tag Archives: risk management

Why Trust Science?

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Part 1 of a series of 5 for NextGen Journal.

What’s wrong with these statements?

  • I believe in global warming.
  • I don’t believe in global warming.
  • We should hear all sides of the climate change debate and decide for ourselves.

Don’t see it? How about these?

  • I believe in photosynthesis.
  • I don’t believe in Newton’s Laws of Motion.
  • We should hear all sides of the quantum mechanics debate and decide for ourselves.

Climate change is a scientific phenomenon, rooted in physics and chemistry. All I did was substitute in other scientific phenomena, and the statements suddenly sounded wacky and irrational.

Perhaps we have become desensitized by people conflating opinion with fact when it comes to climate change. However, the positions of politicians or media outlets do not make the climate system any less of a physical process. Unlike, say, ideology, there is a physical truth out there.

If there is a physical truth, there are also wrong answers and false explanations. In scientific issues, not every “belief” is equally valid.

Of course, the physical truth is elusive, and facts are not always clear-cut. Data requires interpretation and a lot of math. Uncertainty is omnipresent and must be quantified. These processes require training, as nobody is born with all the skills required to be a good scientist. Again, the complex nature of the physical world means that some voices are more important than others.

Does that mean we should blindly accept whatever a scientist says, just because they have a Ph.D.? Of course not. People aren’t perfect, and scientists are no exception.

However, the institution of science has a pretty good system to weed out incorrect or unsupported theories. It involves peer review, and critical thinking, and falsifiability. We can’t completely prove anything right – not one hundred percent – so scientists try really hard to prove a given theory wrong. If they can’t, their confidence in its accuracy goes up. Peter Watts describes this process in more colourful terms: “You put your model out there in the coliseum, and a bunch of guys in white coats kick the s**t out of it. If it’s still alive when the dust clears, your brainchild receives conditional acceptance. It does not get rejected. This time.”

Peer review is an imperfect process, but it’s far better than nothing. Combined with the technical skill and experience of scientists, it makes the words of the scientific community far more trustworthy than the words of a politician or a journalist. That doesn’t mean that science is always right. But, if you had to put your money on it, who would you bet on?

The issue is further complicated by the fact that scientists are rarely unanimous. Often, the issue at question is truly a mystery, and the disagreement is widespread. What causes El Niño conditions in the Pacific Ocean? Science can’t give us a clear answer yet.

However, sometimes disagreement is restricted to the extreme minority. This is called a consensus. It doesn’t imply unanimity, and it doesn’t mean that the issue is closed, but general confidence in a theory is so high that science accepts it and moves on. Even today, a few researchers will tell you that HIV doesn’t cause AIDS, or that secondhand smoke isn’t harmful to your health. But that doesn’t stop medical scientists from studying the finer details of such diseases, or governments from funding programs to help people quit smoking. Science isn’t a majority-rules democracy, but if virtually all scientists have the same position on an issue, they probably have some pretty good reasons.

If science is never certain, and almost never unanimous, what are we supposed to do? How do we choose who to trust? Trusting nobody but yourself would be a poor choice. Chances are, others are more qualified than you, and you don’t hold the entirety of human knowledge in your head. For policy-relevant science, ignoring the issue completely until one side is proven right could also be disastrous. Inaction itself is a policy choice, which we see in some governments’ responses to climate change.

Let’s bring the whole issue down to a more personal level. Imagine you were ill, and twenty well-respected doctors independently examined you and said that surgery was required to save your life. One doctor, however, said that your illness was all in your mind, that you were healthy as a horse. Should you wait in bed until the doctors all agreed? Should you go home to avoid surgery that might be unnecessary? Or should you pay attention to the relative size and credibility of each group, as well as the risks involved, and choose the course of action that would most likely save your life?

What Can One Person Do?

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Next week, I will be giving a speech on climate change to the green committee of a local United Church. They are particularly interested in science and solutions, so I wrote the following script, drawing heavily from my previous presentations. I would really appreciate feedback and suggestions for this presentation.

Citations will be on the slides (which I haven’t made yet), so they’re not in the text of this script. Let me know if there’s a particular reference you’re wondering about, but they’re probably common knowledge within this community by now.

Enjoy!

Climate change is depressing. I know that really well, because I’ve been studying it for over two years. I’m quite practiced at keeping the scary stuff contained in the analytical part of my brain, and not thinking of the implications – because the implications make you feel powerless. I’m sure that all of us here wish we could stop global warming on our own. So we work hard to reduce our carbon footprints, and then we feel guilty every time we take the car out or buy something that was made in China or turn up the heat a degree.

The truth is, though, the infrastructure of our society doesn’t support a low-carbon lifestyle. Look at the quality of public transit in Winnipeg, or the price of local food. We can work all we want at changing our practices, but it’s an uphill battle. If we change the infrastructure, though – if we put a price on carbon so that sustainable practices are cheaper and easier than using fossil fuels – people everywhere will subsequently change their practices.

Currently, governments – particularly in North America – aren’t too interested in sustainable infrastructure, because they don’t think people care. Politicians only say what they think people want to hear. So, should we go dress up as polar bears and protest in front of Parliament to show them we care? That might work, but they will probably just see us as crazy environmentalists, a fringe group. We need a critical mass of people that care about climate change, understand the problem, and want to fix it. An effective solution requires top-down organization, but that won’t happen until there’s a bottom-up, grassroots movement of people who care.

I believe that the most effective action one person can take in the fight against global warming is to talk to others and educate others. I believe most people are good, and sane, and reasonable. They do the best they can, given their level of awareness. If we increase that awareness, we’ll gain political will for a solution. And so, in an effort to practice what I preach, I’m going to talk to you about the issue.

The science that led us to the modern concern about climate change began all the way back in 1824, when a man named Joseph Fourier discovered the greenhouse effect. Gases such as carbon dioxide make up less than one percent of the Earth’s atmosphere, but they trap enough heat to keep the Earth over 30 degrees Celsius warmer than it would be otherwise.

Without greenhouse gases, there could be no life on Earth, so they’re a very good thing – until their concentration changes. If you double the amount of CO2 in the air, the planet will warm, on average, somewhere around 3 degrees. The first person to realize that humans could cause this kind of a change, through the burning of fossil fuels releasing CO2, was Svante Arrhenius, in 1897. So this is not a new theory by any means.

For a long time, scientists assumed that any CO2 we emitted would just get absorbed by the oceans. In 1957, Roger Revelle showed that wasn’t true. The very next year, Charles Keeling decided to test this out, and started measuring the carbon dioxide content of the atmosphere. Now, Arrhenius had assumed that it would take thousands of years to double CO2 from the preindustrial value of 280 ppm (which we know from ice cores), but the way we’re going, we’ll get there in just a few decades. We’ve already reached 390 ppm. That might not seem like a lot, but 390 ppm of arsenic in your coffee would kill you. Small changes can have big effects.

Around the 1970s, scientists realized that people were exerting another influence on the climate. Many forms of air pollution, known as aerosols, have a cooling effect on the planet. In the 70s, the warming from greenhouse gases and the cooling from aerosols were cancelling each other out, and scientists were split as to which way it would go. There was one paper, by Stephen Schneider, which even said it could be possible to cause an ice age, if we put out enough aerosols and greenhouse gases stayed constant. However, as climate models improved, and governments started to regulate air pollution, a scientific consensus emerged that greenhouse gases would win out. Global warming was coming – it was just a question of when.

In 1988, James Hansen, who is arguably the top climate scientist in the world today, claimed it had arrived. In a famous testimony to the U.S. Congress, he said that “the greenhouse effect has been detected, and it is changing our climate now.” Many scientists weren’t so sure, and thought it was too early to make such a bold statement, but Hansen turned out to be right. Since about 1975, the world has been warming, more quickly than it has for at least the last 55 million years.

Over the past decade, scientists have even been able to rule out the possibility that the warming is caused by something else, like a natural cycle. Different causes of climate change have slightly different effects – like the pattern of warming in different layers of the atmosphere, the amount of warming in summer compared to winter, or at night compared to in the day, and so on. Ben Santer pioneered attribution studies: examining these effects in order to pinpoint a specific cause. And so far, nobody has been able to explain how the recent warming could not be caused by us.

Today, there is a remarkable amount of scientific agreement surrounding this issue. Between 97 and 98% of climate scientists, virtually 100% of peer-reviewed studies, and every scientific organization in the world agree that humans are causing the Earth to warm. The evidence for climate change is not a house of cards, where you take one piece out and the whole theory falls apart. It’s more like a mountain. Scrape a handful of pebbles off the top, but the mountain is still there.

However, if you take a step outside of the academic community, this convergence of evidence is more or less invisible. The majority of newspaper articles, from respected outlets like the New York Times or the Wall Street Journal, spend at least as much time arguing against this consensus as they do arguing for it. They present ideas such as “maybe it’s a natural cycle” or “CO2 has no effect on climate” that scientists disproved years ago. The media is stuck in the past. Some of them are only stuck in the 1980s, but others are stuck all the way back in 1800. Why is it like this?

Part of it comes from good, but misguided, intentions. When it comes to climate change, most journalists follow the rule of balance: presenting “two equal sides”, staying neutral, letting the reader form their own opinion. This works well when the so-called controversy is one of political or social nature, like tax levels or capital punishment. In these cases, there is no right answer, and people are usually split into two camps. But when the question at hand is one of science, there is a right answer – even if we haven’t found it yet – so some explanations are better than others, and some can be totally wrong. Would you let somebody form their own opinion on Newton’s Laws of Motion or the reality of photosynthesis? Sometimes scientists are split into two equal groups, but sometimes they’re split into three or four or even a dozen. How do you represent that as two equal sides? Sometimes, like we see with climate change, pretty much all the scientists are in agreement, and the two or three percent which aren’t don’t really publish, because they can’t back up their statements and nobody really takes them seriously. So framing these two groups as having equal weight in the scientific community is completely incorrect. It exaggerates the extreme minority, and suppresses everyone else. Being objective is not always the same as being neutral, and it’s particularly important to remember that when our future is at stake.

Another reason to frame climate science as controversial is that it makes for a much better story. Who really wants to read about scientists agreeing on everything? Journalists try to write stories that are exciting. Unfortunately, that goal can begin to overshadow accuracy.

Also, there are fewer journalists than there used to be, and there are almost no science journalists in the mainstream media – general reporters cover science issues instead. Also, a few decades ago, journalists used to get a week or two to write a story. Now they often have less than a day, because speed and availability of news has become more important than quality.

However, perhaps the most important – and disturbing – explanation for this inaccurate framing is that the media has been very compliant in spreading the message of climate change deniers. They call themselves skeptics, but I don’t think that’s accurate. A true skeptic will only accept a claim given sufficient evidence. That’s a good thing, and all scientists should be skeptics. But it’s easy to see that these people will never accept human-caused climate change, no matter what the evidence. At the same time, they blindly accept any shred of information that seems to support their cause, without applying any skepticism at all. That’s denial, so let’s not compliment them by calling them skeptics.

Climate change deniers will use whatever they can get – whether or not it’s legitimate, whether or not it’s honest – as proof that climate change is natural, or nonexistent, or a global conspiracy. They’ll tell you that volcanoes emit more CO2 than humans, but volcanoes actually emit about 1% of what we do. They’ll say that global warming has stopped because 2008 was cooler than 2007. If climatologists organize a public lecture in effort to communicate accurate scientific information, they’ll say that scientists are dogmatic and subscribe to censorship and will not allow any other opinions to be considered.

Some of these questionable sources are organizations, like a dozen or so lobby groups that have been paid a lot of money by oil companies to say that global warming is fake. Some of them are individuals, like US Senator James Inhofe, who was the environment chair under George W. Bush, and says that “global warming is the greatest hoax ever imposed upon the American people.” Some of them have financial motivations, and some of them have ideological motivations, but their motivations don’t really matter – all that matters is that they are saying things that are inaccurate, and misleading, and just plain wrong.

There has been a recent, and very disturbing, new tactic of deniers. Instead of attacking the science, they’ve begun to attack the integrity of individual scientists. In November 2009, they stole thirteen years of emails from a top climate research group in the UK, and spread stories all over the media that said scientists were caught fudging their data and censoring critics. Since then, they’ve been cleared of these charges by eight independent investigations, but you wouldn’t know it by reading the newspaper. For months, nearly every media outlet in the developed world spread what was, essentially, libel, and the only one that has formally apologized for its inaccurate coverage is the BBC.

In the meantime, there has been tremendous personal impact on the scientists involved. Many of them have received death threats, and Phil Jones, the director of the research group, was nearly driven to suicide. Another scientist, who wishes to remain anonymous, had a dead animal dumped on his doorstep and now travels with bodyguards. The Republican Party, which prides itself on fiscal responsibility, is pushing for more and more investigations, because they just can’t accept that the scientists are innocent…and James Inhofe, the “global warming is a hoax” guy, attempted to criminally prosecute seventeen researchers, most of whom had done nothing but occasionally correspond with the scientists who had their emails stolen. It’s McCarthyism all over again.

So this is where we are. Where are we going?

The Intergovernmental Panel on Climate Change, or IPCC, which collects and summarizes all the scientific literature about climate change, said in 2007 that under a business-as-usual scenario, where we keep going the way we’re going, the world will warm somewhere around 4 degrees Celsius by 2100. Unfortunately, this report was out of date almost as soon as it was published, and has widely been criticized for being too conservative. The British Meteorological Office published an updated figure in 2009 that estimated we will reach 4 degrees by the 2070s.

I will still be alive then (I hope!). I will likely have kids and even grandkids by then. I’ve spent a lot of time researching climate change, and the prospect of a 4 degree rise is terrifying to me. At 4 degrees, we will have lost control of the climate – even if we stop emitting greenhouse gases, positive feedbacks in the climate system will make sure the warming continues. We will have committed somewhere between 40 and 70 percent of the world’s species to extinction. Prehistoric records indicate that we can expect 40 to 80 metres of eventual sea level rise – it will take thousands of years to get there, but many coastal cities will be swamped within the first century. Countries – maybe even developed countries – will be at war over food and water. All this…within my lifetime.

And look at our current response. We seem to be spending more time attacking the scientists who discovered the problem than we are negotiating policy to fix it. We should have started reducing our greenhouse gas emissions twenty years ago, but if we start now, and work really hard, we do have a shot at stopping the warming at a point where we stay in control. Technically, we can do it. It’s going to take an unprecedented amount of political will and international communication

Everybody wants to know, “What can I do?” to fix the problem. Now, magazines everywhere are happy to tell you “10 easy ways to reduce your carbon footprint” – ride your bike, and compost, and buy organic spinach. That’s not really going to help. Say that enough people reduce their demand on fossil fuels: supply and demand dictates that the price will go down, and someone else will say, “Hey, gas is cheap!” and use more of it. Grassroots sentiment isn’t going to be enough. We need a price on carbon, whether it’s a carbon tax or cap-and-trade…but governments won’t do that until a critical mass of people demand it.

So what can you do? You can work on achieving that critical mass. Engage the apathetic. Educate people. Talk to them about climate change – it’s scary stuff, but suck it up. We’re all going to need to face it. Help them to understand and care about the problem. Don’t worry about the crazy people who shout about socialist conspiracies, they’re not worth your time. They’re very loud, but there’s not really very many of them. And in the end, we all get one vote.

Where Activism Fails

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Cross-posted from NextGen Journal

This weekend, 10 000 young people converged in Washington, D.C. and protested the American government’s inaction on climate change. Students stood in front of government buildings wearing green hard hats, holding signs saying “Make Polluters Pay, Not the EPA”. Students stormed the House of Representatives and sang a song about climate change, to the tune of the American national anthem. Fifteen minutes with President Obama, who agreed with their concerns but said “I can’t do this alone”, was PowerShift 2011’s biggest accomplishment.

This isn’t working.

The climate change mitigation lobby is currently a fringe group, at least in North America. It’s mostly made up of university students who mimic the campus protests of the 1960s, creating images that scream “socialism” to baby boomers who witnessed the original events. Governments, which are mostly made up of said baby boomers, largely ignore such fringe groups. Elected officials say what they think people want to hear, and most people don’t seem to care about climate change.

So what should we do instead? We don’t have a lot of money or connections to wealthy businesses. Youth don’t even vote in large enough numbers for governments to care what they want. What we do have, however, are facts on our side. We have the weight of the entire scientific community, agreeing that humans are causing a potentially catastrophic climate change which will only be stopped by major international action.

Instead of attempting to communicate with elected officials by marching around in front of their offices with our faces painted, I think we should focus our efforts on the public. If governments think people don’t care about climate change, we have to reverse that trend.

I believe that anyone who truly understands this issue will care about it and want to fix it. Who could honestly examine the overwhelming evidence for anthropogenic climate change and still have reasonable doubts about its existence? Who wouldn’t want to prevent future wars, famines, extinctions, and waves of environmental refugees? Of course, there are the crazies who will scream about “climate scientists in Al Gore’s pocket” and “the world needs more CO2” no matter what we tell them, but we shouldn’t bother engaging with these people. Instead, we should engage with those who are constantly exposed to the crazies, and who are at risk of dismissing climate change because they think people are still debating its existence.

We need public education to create a social movement, but not like the “Green Movement” in 2007 when magazines everywhere advertised “10 easy ways to reduce your carbon footprint”. We need people to understand the severity of climate change, and to see that planting a tree and buying organic lettuce will not solve the problem. We need people to understand that meaningful action, such as putting a price on carbon, is necessary to solve the problem.

Climate change education will spread most easily through the media, whether it is mass media or new media. People need to be aware of the level of scientific support surrounding this issue, and the reality that climate scientists are not ignorant or fraudulent. Researchers know that correlation does not equal causation, and they know that the climate has changed in the past. Many people still take these arguments seriously, though, because they are thrown around and not challenged. We need to challenge the media outlets that have spread dangerous, libelous misinformation regarding climate change for years. We need to challenge them on the level of lawsuits, not on the level of writing letters to the editor.

It is vital to engage with the apathetic and show them why they should care. Apathetic youth are particularly problematic. Why should the government care about the needs of the next generation when most of its members don’t even vote? We have to make the youth vote strong enough that political parties will compete for its support, just like they do with the ethnic vote and the women’s vote. As Canadian comedian and political analyst Rick Mercer said, “If you are between the ages of 18 and 25, and want to scare the hell out of the people who run this country – this time around, do the unexpected: vote.”

When faced with a depressing reality, many will turn away and ignore the problem. However, the only way to prevent the scary stuff from happening is to suck it up and face it. Just because we wasted 20 years of potential action and got ourselves into a bad situation doesn’t mean we should throw up our hands and give up. It’s never too late to act, because this bad situation can always get worse if we let it.

The Rest of the World

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Here in North America, we are surrounded with rhetoric denouncing the feasibility of climate change mitigation. It’s not possible to reduce our emissions, people say. It’s not worth it.

The situation in the U.S. Congress regarding this issue is becoming so bizarre that hopes for an international agreement to reduce greenhouse gas emissions have grown faint. Without the U.S. on board, many countries (see: Canada) will bail out entirely.

Not all countries are waiting for everyone else, however. Many developed countries, particularly in Europe, have gone ahead and achieved significant cuts in their emissions. Let’s take a step out of the little bubble of North America and see what the rest of the world managed to do while we bickered about whether or not there was even a problem.

***

Countries: the European Union (EU), representing most of Europe

Emission Targets: 20% below 1990 levels by 2020

How They’ll Get There: The EU started a cap-and-trade system in 2005. They also plan to target energy efficiency and develop the use of renewable energy.

How They’re Doing : The total emissions of the EU have declined slightly since 1990. This is partly because many Eastern European countries are still transitioning from communism, and their emissions are fairly low while their economies recover. However, some rich countries such as Germany, Sweden, Denmark, and the UK have made significant cuts in their emissions, and, as of 2008, were already around 10-20% below 1990 levels.

***

Country: the United Kingdom (UK)

Emission Targets: 12.5% below 1990 levels by 2012, as per their Kyoto targets. Through their Climate Change Acts, the UK has also set a goal of 80% below 1990 levels by 2050.

How They’ll Get There: The government is aiming for 40% of their energy to come from low-carbon sources (both renewable and nuclear). They are also focusing on efficiency, and planning a cap-and-trade system.

How They’re Doing: The UK is well on track to meet, and even exceed, their Kyoto agreements. By 2010, their emissions were predicted to be 11% below their Kyoto targets.

***

Country: Norway

Emission Targets: Norway has some of the most ambitious targets in the world. Not only are they aiming for emissions to be 30% below 1990 levels by 2020, they are planning a carbon-neutral economy – 100% cuts – by 2050. If a major international agreement comes to pass, like Copenhagen was supposed to be, they will pledge for carbon neutrality by 2030.

How They’ll Get There: In addition to their cap and trade system, Norway is investing a lot of money into carbon capture and storage (CCS). They have also introduced taxes on natural gas and stricter efficiency standards for new houses.

How They’re Doing: Norway’s emissions have increased by 8% since 1990. Hopefully their extensive plans will reverse that trend.

***

Country: Australia

Emission targets: If an international agreement comes to pass, Australia will reduce their emissions to 25% below 2000 levels by 2020. Otherwise, they will shift that target to 5-15%. Normally, using a baseline that’s later than the standard 1990 is a warning sign, a clever trick that governments use to make their targets look stricter than they are (see: Canada). However, since Australia’s emissions fell slightly between 1990 and 2000, the equivalent target with respect to 1990 is actually more than 25%.

How They’ll Get There: The Australian Parliament has had difficulty passing cap-and-trade legislation. They are hoping to implement this eventually, but will focus on energy efficiency and renewables in the mean time.

How They’re Doing: Originally, Australia refused to sign Kyoto, but in 2007 a new Prime Minister, Kevin Rudd, was elected. He committed the country to Kyoto targets, just a little late. So far, it looks like Australia will easily meet their targets of 8% over 1990 levels by 2012.

***

Country: Japan

Emission targets: Japan has set solid targets of 25% below 1990 levels by 2020, and 80% by 2050.

How They’ll Get There: Japan has a cap-and-trade system, and is considering a carbon tax. They also want 10% of their energy to come from renewables by 2020.

How They’re Doing: Japan’s emissions have increased slightly since 1990. As of 2008, they were about 6% above 1990 levels.

***

Country: Canada

Emission targets: The Canadian government has pledged to reduce emissions to 17% below 2005 levels by 2020. However, emissions in 2005 were quite a bit higher than they were in 1990. When you adjust this estimate to the standard baseline, it’s actually a 2.5% increase. The Environment Canada website describes this as an “ambitious target”. Go figure!

How They’ll Get There: So far, the Canadian government has tightened up fuel efficiency standards for passenger vehicles, but that’s about it. The current administration refuses to consider meaningful action until the United States does. In fact, the House of Commons recently passed a bill setting meaningful emission targets (20% below 1990 levels by 2020, and 80% by 2050)…but the Senate, which has a Conservative majority, voted the bill down with absolutely no debate. Given the fact that Senators are appointed by Prime Ministers, not elected by citizens, it’s hard to see this action as anything less than anti-democratic.

How They’re Doing:By 2008, Canadian emissions had soared to 24% above 1990 levels.

***

This data almost makes me feel ashamed to be Canadian, to be a part of such an obstructionist country. Look at what countries in Europe have managed to do. It wasn’t impossible, like so many North American politicians warned. And then look at countries like the United States and Canada, that have not only failed to reduce their emissions, but have actively worked against any kind of a plan to do so.

Future generations will not look on us kindly. We will become the villains of our own history books.

***

Update: By popular request:

Country: United States of America

Emission targets: None

How They’ll Get There: Despite not having a formal target for emissions, the Environmental Protection Agency (EPA) began to regulate emissions from fossil-fuel fired power plants and refineries in late December. The Republican Party is resorting to all sorts of silliness to try to change this.

How They’re Doing: As of 2008, US emissions were 14% above 1990 levels.

Ozone Depletion and Climate Change

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“Global warming…doesn’t that have something to do with the ozone?” Well, no. Environmental issues are not all the same. It’s common for people to confuse climate change and ozone depletion, but they are separate issues – although they are indirectly connected in some interesting ways.

Ozone, which is made of three oxygen atoms stuck together (instead of two, which is what normal oxygen gas is made of), is vital to life on Earth. It forms a layer in the stratosphere, the second layer up in the atmosphere, that is very good at absorbing ultraviolet (UV) radiation from the Sun. UV radiation severely damages organisms if enough of it reaches the surface. The 3% or less that gets through the ozone already gives us sunburns and skin cancer, so you can imagine what the situation would be like if the ozone layer wasn’t there at all.

In the middle of the 20th century, synthetic gases known as chlorofluorocarbons (CFCs) became popular for use in refrigerators and aerosol products, among other applications. They were non-toxic, and did not react easily with other substances, so they were used widely. However, their chemical stability allowed them to last long enough to drift into the stratosphere after they were emitted.

Once in the stratosphere, the CFCs were exposed to UV radiation, which was able to break them down. Free chlorine atoms (Cl) were liberated, a substance that is very reactive indeed. In fact, Cl acts as a catalyst in the decomposition of ozone, allowing two ozone molecules to become three oxygen molecules, losing their UV absorbing power in the process. Since catalysts are not used up in a reaction, the same Cl radical can continue to destroy ozone until it reacts with something else in the atmosphere and is removed.

Over the poles, the stratosphere is cold enough for polar stratospheric clouds (PSCs) to form. These PSCs provided optimum conditions for the most reactive chlorine gas of all to form: ClO (chlorine monoxide). Now there wasn’t just a catalytic cycle of free Cl radicals depleting the ozone, there was also a cycle of ClO. It turns out that Antarctica was more favourable for ozone depletion than the Arctic, both because its temperatures were lower and because its system of wind currents prevented the ozone-depleting substances from drifting out of the area.

Before long, there was a hole in the ozone layer over Antarctica (due to the PSCs), and concentrations were declining in other locations too (due to the basic Cl reactions). The issue became a frontier for scientific research, and scientists Crutzen, Rowland, and Molina won the 1995 Nobel Prize in Chemistry for their work with atmospheric ozone.

In 1987, politicians worldwide decided to ban CFCs under the Montreal Protocol. This movement was largely successful, and the use of CFCs has become nearly negligible, especially in developed nations. They have been replaced with gases that safely decompose before they reach the stratosphere, so they don’t interfere with ozone. The regulations are working: the ozone hole in Antarctica has stabilized, and global stratospheric ozone concentrations have been on the rise since 1993.

In contrast, climate change is a product of greenhouse gases such as carbon dioxide. Unlike CFCs, most of them are not synthetic, and they are released from the burning of fossil fuels (coal, oil, and natural gas), not specific products such as refrigerators. Rather than destroying a natural process, like CFCs do, they strengthen one to the point of harm: the greenhouse effect. This phenomenon, which traps heat in the atmosphere, is absolutely vital, as the Earth would be too cold to support life without it. Increasing the concentrations of greenhouse gases with fossil fuels becomes too much of a good thing, though, as the greenhouse effect traps more heat, warming the planet up.

Just a few degrees Celsius of warming can cause major problems, as agricultural zones, wind and ocean currents, and precipitation patterns shift. The sea level rises, submerging coastal cities. Many species go extinct, as the climate changes faster than they can adapt. Basically, the definition of “normal” in which our civilization has developed and thrived is changing, and we can’t count on that stability any more.

Unlike the Montreal Protocol, efforts to reduce greenhouse gas emissions have more or less failed. Fossil fuels permeate every part of our lives, and until we shift the economy to run on clean energy instead, convincing governments to commit to reductions will be difficult at best. It remains to be seen whether or not we can successfully address this problem, like we did with ozone depletion.

Although these two issues are separate, they have some interesting connections. For example, PSCs form in cold areas of the stratosphere. That’s why the ozone hole is over Antarctica, and not somewhere else. Unfortunately, global warming is, paradoxically, cooling the stratosphere, as a stronger greenhouse effect means that less heat reaches the stratosphere. Therefore, as climate change progresses, it will make it easier for the ozone depletion reactions to occur, even though there are fewer CFCs.

Additionally, CFCs are very strong greenhouse gases, but their use has drastically reduced so their radiative effects are of lesser concern to us. However, some of their replacements, HFCs, are greenhouse gases of similar strength. They don’t deplete the ozone, but, per molecule, they can be thousands of times stronger than carbon dioxide at trapping heat. Currently, their atmospheric concentrations are low enough that they contribute far less forcing than carbon dioxide, but it wouldn’t take a large increase in HFCs to put us in a bad situation, simply because they are so potent.

Finally, these two issues are similar in that ozone depletion provides a smaller-scale analogue for the kinds of political and economic changes we will have to make to address climate change:

  1. Unintended chemical side effects of our economy posed a serious threat to all species, including our own.
  2. Industry representatives and free-market fundamentalists fought tooth and nail against conclusive scientific findings, and the public became bewildered in a sea of misinformation.
  3. Governments worked together to find sensible alternatives and more or less solved the problem.

We’ve already seen the first two events happen with climate change. Will we see the third as well?

Nuclear Power in Context

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Since its birth, nuclear power has been a target of environmental activism. To be fair, when nuclear power goes wrong, it goes wrong in a bad way. Take a look at what’s happening in Japan right now. Friday’s tsumani damaged the Fukushima Daiichi power plant, and several of its reactors have experienced partial meltdowns. Radiation from the nuclear reactions has been released into the surrounding environment, and could endanger public health in the immediate area, causing cancer and birth defects.

Nuclear disasters are horrifying, and this is by no means the worst that has happened. However, nuclear isn’t the only form of energy that experiences periodic disasters. In fact, over the past century, hydroelectric disasters have killed more people than all other forms of energy disasters combined.

(Sovacool et al, 2008, Fig. 1).

So why do we worry so much more about nuclear power disasters? Is it because the idea of the resulting radiation is more disturbing than the prospect of a dam breaking, even if it’s far less common?

However, an energy source can kill people without a large-scale disaster occurring. Let’s look at fossil fuels. Think of all the miners killed by coal accidents, all the people killed by smog inhalation or exposure to toxic chemicals (such as heavy metals) that are present in fossil fuels, deaths due to gas leaks, civilians killed by wars over oil, and so on. It’s difficult to quantify these numbers, because fossil fuels have been in use for centuries, but they clearly exceed the 4,000 or so deaths due to nuclear power accidents (as well as any other deaths due to nuclear power, such as uranium mining).

We must also look at the deaths due to climate change, which fossil fuel burning has induced. The World Health Organization estimates that over 150 000 people died as a result of climate change in 2000 alone. This annual rate will increase as the warming progresses. If we don’t step away from fossil fuels in time, they could lead to a devastating amount of death and suffering.

Fossil fuels are silent, passive, indirect killers which end up being far more destructive to human life than nuclear power. However, much of the public remains opposed to nuclear energy, and I believe this is a case of “letting perfect be the enemy of good”. I feel that we hold nuclear power to an impossible standard, that we expect it to be perfect. It’s certainly not perfect, but it’s far better than the existing system, which desperately needs to be replaced.

There are also exciting developments in nuclear technology that could make it safer and more efficient. In his recent book, top climatologist James Hansen described “fast reactors“, which are a vast improvement over the previous generations of nuclear reactors. It’s also possible to use uranium-238 as fuel, which makes up 99.3% of all natural uranium, and is usually thrown away as nuclear waste because reactors aren’t equipped to use it. Another alternative is to use thorium, a safer and more common element. If we pursue these technologies, the major downsides of nuclear power – safety and waste concerns – could diminish substantially.

Renewable sources of energy, such as solar, wind, and geothermal, are safer than nuclear power, and also have a lower carbon footprint per kWh (Sovacool, 2008b, Table 8). They are clearly the ideal choice in the long run, but they can’t solve the problem completely, at least not yet. Cost is a barrier, as is the problem of storing and transporting the electricity they generate. Maybe a few decades down the line smart grids will become a reality, and we will be able to have an energy economy that is fully renewable. If we wait for that perfect situation before doing anything, though, we will overshoot and cause far more climate change than we can deal with.

I don’t know if I would describe myself as “pro-nuclear”, but I am definitely “anti-fossil-fuel”. I am aware of the risks nuclear power poses, and feel that, from a risk management perspective, it is still preferable to coal and oil by a long shot. Solving climate change will require a multi-faceted energy economy, and it would be foolish to rule out one viable option simply because it isn’t perfect.

Extinction and Climate

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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

The Pendulum

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Cross-posted from NextGen Journal

A few years ago, climate change mitigation became a major political issue. Before 2005, governments certainly knew that human-caused climate change was a serious problem – but the public knew next to nothing about it, so there was no incentive to act. However, between 2005 and 2007, a perfect storm of events splashed the reality of climate change onto the world stage.

The Kyoto Protocol, an international agreement to reduce greenhouse gas emissions, finally came into force in early 2005, after years of negotiation. The United States refused to sign, and Australia signed on a little late, but every other developed nation in the world agreed to emission targets. Here in Canada, the Liberal government enthusiastically pledged its support for Kyoto. My local newspaper ran editorials exploring the different ways we could meet our targets, through combinations of clean energy, green infrastructure, and efficiency standards.

The summer of 2005 was a wake-up call for the United States, as Hurricane Katrina mercilessly demonstrated the amount of damage that extreme weather can bring. It’s impossible to say, at least with our current technology, whether or not Katrina was caused or even worsened by a warming planet. However, such devastating storms will become the norm as climate change progresses. Scientists aren’t sure whether or not hurricanes will become more frequent in a warming world, but the average hurricane is expected to become stronger and more damaging, and we are already beginning to see this rise in storm intensity. Katrina gave us an example of what we can expect from climate change – even if it wasn’t a direct effect in itself – and the world was shocked by the suffering that ensued.

2006 marked the release of An Inconvenient Truth, Al Gore’s Academy Award-winning documentary about climate change. For scientists studying climate, the film was an admirable, up-to-date example of science communication, albeit with a few minor errors and oversimplifications. However, for citizens new to the issue (I particularly remember my classmates in grade 9 social studies discussing the film), An Inconvenient Truth was a disturbing reality check – scarier than any horror movie, because it was real.

The major scientific event of 2007 was a drastic, unexpected drop in Arctic summer sea ice. That season’s melt was exacerbated by coincidental weather conditions, so the next years weren’t quite as bad, but the trend was still worrying, to say the least. The research community had assumed that summer ice would stick around for at least a century, but this timescale was soon halved and quartered as ice melt exceeded even the worst projections.

By 2007, lead-up to the 2008 US presidential election was underway, and political awareness of climate change was obvious. It was no surprise that Democrat Barack Obama had ambitious plans to cut greenhouse gas emissions, but even the Republicans seemed to be on board. During his time in office, George W. Bush had insisted that, since climate change could be natural, any mitigating action was not worth the economic risk. Republican presidential candidates seemed to realize that continuing to adopt this attitude would be political suicide. The most extreme example, John McCain, who would eventually win the Republican presidential nomination, had emissions targets only slightly less extensive than Obama’s. As he said in 2007,

The world is already feeling the powerful effects of global warming, and far more dire consequences are predicted if we let the growing deluge of greenhouse gas emissions continue, and wreak havoc with God’s creation…The problem isn’t a Hollywood invention nor is doing something about it a vanity of Cassandra like hysterics. It is a serious and urgent economic, environmental and national security challenge.

However, McCain, once an author of a bill designed to cut greenhouse gas emissions, would soon completely change his stance. By 2010, he was asserting that cap-and-trade legislation was unnecessary and carbon dioxide posed no harm to the American people. He even went so far as to question the political motivations of science he once wholly accepted:

I think [global warming is] an inexact science, and there has been more and more questioning about some of the conclusions that were reached concerning climate change. And I believe that everybody in the world deserves correct answers whether the scientific conclusions were flawed by outside influences. There’s great questions about it that need to be resolved.

The story of John McCain isn’t too surprising. Politicians frequently base their statements on public sentiment rather than personal opinion. They say what people want to hear, rather than what they truly believe is important. This aspect of our political system is depressing, but persistent. The real question, though, regards what changed public sentiment so quickly. Why did politicians like McCain feel compelled to denounce the importance of action on this problem, or even the existence of the problem itself? What happened since 2007 that made the pendulum swing so far in the other direction?

Strike one was the economy. The global recession that began in 2008 was the largest since the Great Depression, and concern for all other problems promptly went down the drain. It’s understandable for citizens to not worry about the environment when they don’t even have the means to feed and clothe their children properly. However, for governments to not realize the long-term economic implications of allowing climate change to continue, along with the potential job-creating benefits of a new energy economy, was disappointing, even though it wasn’t surprising.

Strike two was the all-out war on climate science, spearheaded by the fossil fuel industry and the far right. This PR campaign has been underway since the early 1990s, but was kicked up a notch just over a year ago. Since public understanding of the causes and effects of global warming was growing, and the science was becoming more solid by the month, the PR tactics changed. Instead of attacking the science, they attacked the integrity of the scientists. The most extreme example occurred in November 2009, when private correspondence between top climate researchers was stolen, spread on the Internet, and spun in an attempt to cast doubt on the scientists’ motives. This event, known as “Climategate”, spurred a great deal of anger among the political right, and everything from bitter editorials to death threats against scientists ensued. Perhaps most distressingly, by the time investigations found that the scientists involved were innocent, and the reality of climate change untouched, Climategate was old news and media outlets failed to adequately follow up on the story. Citizens heard the accusations, but not the exonerations, so political will to cut greenhouse gas emissions slipped even further.

Strike three – well, there has been no strike three, and a good thing too. Strikes one and two were so bad that some are hoping the pendulum has swung as far as it can go. It’s certainly difficult to imagine how the situation could get worse. The Kyoto Protocol is set to expire next year, and the Copenhagen meetings failed to create a replacement. As it was, many developed nations failed to meet their targets, and the Canadian government backed out completely.

The possibility of federal climate legislation for the United States is laughable now that not a single Republican Senator thinks action is necessary, and most doubt the reality of the problem, choosing to believe that the entire scientific community is out to lunch and/or an agent of conspiracy. President Obama’s director of climate policy, Carol Browner, recently left her position, although none of her major goals had been met. Obama’s recent State of the Union address included lots of hopeful statements about clean energy, but absolutely no mention of climate change, as if merely acknowledging the most pressing reason for a new energy economy would be political suicide. The time-honoured tradition of saying what the public wants to hear has even reached Obama, the man who promised change.

In Canada, legislation to simply set targets for emission reduction passed the House of Commons (made of elected representatives), but the Senate (composed of appointed politicians) chose to use their newfound Conservative majority to strike down the bill with no debate whatsoever, in a blatantly undemocratic move that has not happened since the 1930s. The Canadian government is all for a new energy economy, but not one based on environmental and social responsibility. The Alberta tar sands, which are substantially more polluting and carbon-intensive than traditional oil, continue to expand, and both federal and provincial governments are worryingly enthusiastic.

From 2005 to 2007, politics was high on promises of mitigation, but low on delivery. Since then, it has been devoid of both. It’s starting to seem as if it will take a major global disaster that can be unquestionably tied to climate change for governments to get their act together.

This would all be very well if there was no lag time between cause and effect in the climate system, but it doesn’t work that way. It takes several decades for all the warming in the pipeline to show up. If we waited until climate change became unbearable, and then cut off our emissions completely, the situation would still get worse for decades before it stabilized.

The worldwide failure of governments to take action on climate change is baffling. It seems that the best they can do is occasionally promise to fix the problem, but never actually get started. If this continues for much longer, we’re all going to pay the price for their mistakes – and so will people for generations to come.

Storms of my Grandchildren

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I hope everyone had a fun and relaxing Christmas. Here’s a book I’ve been meaning to review for a while.

The worst part of the recent book by NASA climatologist James Hansen is, undoubtedly, the subtitle. The truth about the coming climate catastrophe and our last chance to save humanity – really? That doesn’t sound like the intrinsic, subdued style of Dr. Hansen. In my opinion, it simply alienates the very audience we’re trying to reach: moderate, concerned non-scientists.

The inside of the book is much better. While he couldn’t resist slipping in a good deal of hard science (and, in my opinion, these were the best parts), the real focus was on climate policy, and the relationship between science and policy. Hansen struggled with the prospect of becoming involved in policy discussions, but soon realized that he didn’t want his grandchildren, years from now, to look back at his work and say, “Opa understood what was happening, but he did not make it clear.”

Hansen is very good at distinguishing between his scientific work and his opinions on policy, and makes no secret of which he would rather spend time on. “I prefer to just do science,” he writes in the introduction. “It’s more pleasant, especially when you are having some success in your investigations. If I must serve as a witness, I intend to testify and then get back to the laboratory, where I am comfortable. That is what I intend to do when this book is finished.”

Hansen’s policy opinions centre on a cap-and-dividend system: a variant of a carbon tax, where revenue is divided evenly among citizens and returned to them. His argument for a carbon tax, rather than cap-and-trade, is compelling, and certainly convinced me. He also advocates the expansion of nuclear power (particularly “fourth-generation” fast nuclear reactors), a moratorium on new coal-generated power plants, and drastically improved efficiency measures.

These recommendations are robust, backed up with lots of empirical data to argue why they would be our best bet to minimize climate change and secure a stable future for generations to come. Hansen is always careful to say when he is speaking as a scientist and when he is speaking as a citizen, and provides a fascinating discussion of the connection between these two roles. As Bill Blakemore from ABC television wrote in correspondence with Hansen, “All communication is biased. What makes the difference between a propagandist on one side and a professional journalist or scientist on the other is not that the journalist or scientist ‘set their biases aside’ but that they are open about them and constantly putting them to the test, ready to change them.”

Despite all this, I love when Hansen puts on his scientist hat. The discussions of climate science in this book, particularly paleoclimate, were gripping. He explains our current knowledge of the climatic circumstances surrounding the Permian-Triassic extinction and the Paleocene-Eocene Thermal Maximum (usually referred to as the PETM). He explains why neither of these events is a suitable analogue for current climate change, as the current rate of introduction of the radiative forcing is faster than anything we can see in the paleoclimatic record.

Be prepared for some pretty terrifying facts about our planet’s “methane hydrate gun”, and how it wasn’t even fully loaded when it went off in the PETM. Also discussed is the dependence of climate sensitivity on forcing: the graph of these two variables is more or less a parabola, as climate sensitivity increases both in Snowball Earth conditions and in Runaway Greenhouse conditions. An extensive discussion of runaway greenhouse is provided, where the forcing occurs so quickly that negative feedbacks don’t have a chance to act before the positive water vapour feedback gets out of control, the oceans boil, and the planet becomes too hot for liquid water to exist. For those who are interested in this scenario, Hansen argues that, if we’re irresponsible about fossil fuels, it is quite possible for current climate change to reach this stage. For those who have less practice separating the scientific part of their brain from the emotional part, I suggest you skip this chapter.

I would recommend this book to everyone interested in climate change. James Hansen is such an important player in climate science, and has arguably contributed more to our knowledge of climate change than just about anyone. Whether it’s for the science, for the policy discussions, or for his try at science fiction in the last chapter, it’s well worth the cover price.

Thoughts from others who have read this book are welcome in the comments, as always.

The Nature of Scientific Consensus

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Cross-posted from NextGen Journal

It is common for one to fail to grasp the difference between “consensus” and “unanimity”.

A consensus does not require agreement from absolutely every member involved. Rather, it is a more general measure of extremely high agreement, high enough to accept and base decisions on. It’s stronger than a majority-rules style of democracy, but does not necessarily equal unanimity. In fact, in the area of science, where the concept of consensus is particularly important, unanimity is nearly impossible.

With the exception of pure mathematics, scientific theories cannot be proven beyond a doubt. Every physical process that researchers study has some amount of irreducible uncertainty – because there is always, no matter how small, a chance that our understanding could be completely wrong. Additionally, science is never “settled”, because there is always more to learn, whatever the field. Even a law as basic as gravity is still being studied by physicists, and it turns out that it gets more complicated the more you look at it.

Despite this inherent uncertainty, scientists have developed consensuses around all sorts of topics. The Earth is approximately oblate-spherical in shape. Smoking cigarettes increases one’s risk of lung cancer. HIV causes AIDS. There’s a tiny chance that these statements are incorrect, but researchers can still have confidence in their accuracy. Incomplete knowledge is not the same as no knowledge.

However, when there is room for doubt, there will usually be doubters. Physicist Richard Lindzen continues to dispute the health risks of smoking (a conversation is recounted in a recent book by James Hansen). Peter Duesberg, an active molecular and cell biologist, prominently opposes the link between HIV and AIDS. Believe it or not, the Flat Earth Society was alive and well until the death of its leader in 2001 – and signs of the society’s renewal are emerging.

As these examples suggest, for a layperson to wait for scientific unanimity before accepting a topic would be absurd. When consensus reaches a certain point, the null hypothesis shifts: the burden of proof is on the contrarians, rather than the theory’s advocates.

Another case study that may seem surprising to many is that of anthropogenic global warming. A strong scientific consensus exists that human activity, mainly the burning of fossil fuels, is exerting a warming influence on the planet’s temperature, which is already beginning to show up in the instrumental record. This phenomenon is contested by less than 3% of publishing climatologists, a negligible amount of peer-reviewed scientific studies (so few that not one showed up in a 2004 survey’s random sample of almost one thousand papers), and no major scientific societies internationally. Additionally, scientists who dispute the existence or causes of climate change tend to have lower academic credibility than those who do not. It becomes apparent that this scientific question warrants “consensus” standing: never quite settled, never quite unanimous, but certainly good enough to go by. The mainstream media does not always reflect this consensus accurately, but it nonetheless exists.

As world leaders meet in Cancun this week to discuss a global policy to prevent or limit future climate change – a prospect that looks less likely by the day – science can only offer so much advice. Climatologists can approximate what levels of emissions cuts are required to prevent unacceptable consequences, but only when the governments of the world decide which consequences they are willing to accept. Can we deal with worldwide food shortages? Rising sea levels? What about a mass extinction? Even after we define “dangerous consequences”, scientists are unsure of exactly how much temperature change will trigger these consequences, as well as how much greenhouse gas emissions will need to be cut, and how quickly, to prevent the temperature change. All they can offer is a range of probabilities and most likely scenarios.

But remember, incomplete and uncertain knowledge is not the same as no knowledge. Of one thing climate scientists are sure: the more greenhouse gas emissions we emit, the more the world will warm, and the harder it will be to deal with the consequences. There’s no reason for you and I to doubt that simple correlation any longer.