Explaining the Seasons on ‘Game of Thrones’

If you haven’t yet watched the television series Game of Thrones or read George R. R. Martin’s A Song of Ice and Fire books on which the show is based, I would urge you to get started (unless you are a small child, in which case I would urge you to wait a few years). The show and the books are both absolute masterpieces (although, as I alluded, definitely not for kids). I’m not usually a big fan of high fantasy, but the character and plot development of this series really pulled me in.

One of the most interesting parts of the series – maybe just for me – is the way the seasons work in Westeros and Essos, the continents explored in Game of Thrones. Winter and summer occur randomly, and can last anywhere from a couple of years to more than a decade. (Here a “year” is presumably defined by a complete rotation of the planet around the Sun, which can be discerned by the stars, rather than by one full cycle of the seasons.)

So what causes these random, multiyear seasons? Many people, George R. R. Martin included, brush off the causes as magical rather than scientific. To those people I say: you have no sense of fun.

After several lunchtime conversations with my friends from UNSW and U of T (few things are more fun than letting a group of climate scientists loose on a question like this), I think I’ve found a mechanism to explain the seasons. My hypothesis is simple, has been known to work on Earth, and satisfies all the criteria I can remember (I only read the books once and I didn’t take notes). I think that “winters” in Westeros are actually miniature ice ages, caused by the same orbital mechanisms which govern ice ages on Earth.

Glacial Cycles on Earth

First let’s look at how ice ages – the cold phases of glacial cycles – work on Earth. At their most basic level, glacial cycles are caused by gravity: the gravity of other planets in the solar system, which influence Earth’s orbit around the Sun. Three main orbital cycles, known as Milankovitch cycles, result:

  1. A 100,000 year cycle in eccentricity: how elliptical (as opposed to circular) Earth’s path around the Sun is.
  2. A 41,000 year cycle in obliquity: the degree of Earth’s axial tilt.
  3. A 26,000 year cycle in precession: what time of year the North Pole is pointing towards the Sun.

These three cycles combine to impact the timing and severity of the seasons in each hemisphere. The way they combine is not simple: the superposition of three sinusoidal functions with different periods is generally a mess, and often one cycle will cancel out the effects of another. However, sometimes the three cycles combine to make the Northern Hemisphere winter relatively warm, and the Northern Hemisphere summer relatively cool.

These conditions are ideal for glacier growth in the Northern Hemisphere. A warmer winter, as long as it’s still below freezing, will often actually cause more snow to fall. A cool summer will prevent that snow from entirely melting. And as soon as you’ve got snow that sticks around for the entire year, a glacier can begin to form.

Then the ice-albedo feedback kicks in. Snow and ice reflect more sunlight than bare ground, meaning less solar radiation is absorbed by the surface. This makes the Earth’s average temperature go down, so even less of the glacier will melt each summer. Now the glacier is larger and can reflect even more sunlight. This positive feedback loop, or “vicious cycle”, is incredibly powerful. Combined with carbon cycle feedbacks, it caused glaciers several kilometres thick to spread over most of North America and Eurasia during the last ice age.

The conditions are reversed in the Southern Hemisphere: relatively cold winters and hot summers, which cause glaciers to recede. However, at this stage in Earth’s history, most of the continents are concentrated in the Northern Hemisphere. The south is mostly ocean, where there are no glaciers to recede. For this reason, the Northern Hemisphere is the one which controls Earth’s glacial cycles.

These ice ages don’t last forever, because sooner or later the Milankovitch cycles will combine in the opposite way: the Northern Hemisphere will have cold winters and hot summers, and its glaciers will start to recede. The ice-albedo feedback will be reversed: less snow and ice means more sunlight is absorbed, which makes the planet warmer, which means there is less snow and ice, and so on.

Glacial Cycles in Westeros?

I propose that Westeros (or rather, the unnamed planet which contains Westeros and Essos and any other undiscovered continents in Game of Thrones; let’s call it Westeros-world) experiences glacial cycles just like Earth, but the periods of the underlying Milankovitch cycles are much shorter – on the order of years to decades. This might imply the presence of very large planets close by, or a high number of planets in the solar system, or even multiple other solar systems which are close enough to exert significant gravitational attraction. As far as I know, all of these ideas are plausible, but I encourage any astronomers in the audience to chime in.

Given the climates of various regions in Game of Thrones, it’s clear that they all exist in the Northern Hemisphere: the further north you go, the colder it gets. The southernmost boundary of the known world is probably somewhere around the equator, because it never starts getting cold again as you travel south. Beyond that, the planet is unexplored, and it’s plausible that the Southern Hemisphere is mainly ocean. The concentration of continents in one hemisphere would allow Milankovitch cycles to induce glacial cycles in Westeros-world.

The glacial periods (“winter”) and interglacials (“summer”) would vary in length – again, on the scale of years to decades – and would appear random: the superposition of three different sine functions has an erratic pattern of peaks and troughs when you zoom in. Of course, the pattern of season lengths would eventually repeat itself, with a period equal to the least common multiple of the three Milankovitch cycle periods. But this least common multiple could be so large – centuries or even millennia – that the seasons would appear random on a human timescale. It’s not hard to believe that the people of Westeros, even the highly educated maesters, would fail to recognize a pattern which took hundreds or thousands of years to repeat.

Of course, within each glacial cycle there would be multiple smaller seasons as the planet revolved around the Sun – the way that regular seasons work on Earth. However, if the axial tilt of Westeros-world was sufficiently small, these regular seasons could be overwhelmed by the glacial cycles to the point where nobody would notice them.

There could be other hypotheses involving fluctuations in solar intensity, frequent volcanoes shooting sulfate aerosols into the stratosphere, or rapid carbon cycle feedbacks. But I think this one is the most plausible, because it’s known to happen on Earth (albeit on a much longer timescale). Can you find any holes? Please go nuts in the comments.

The Day After Tomorrow: A Scientific Critique

The 2004 film The Day After Tomorrow, in which global warming leads to a new ice age, has been vigorously criticized by climate scientists. Why is this? What mistakes in the film led Dr. Andrew Weaver, Canada’s top climate modeller, to claim that “the science-fiction movie The Day After Tomorrow creatively violates every known law of thermodynamics”? What prompted Dr. Gavin Schmidt, NASA climatologist, to say thatThe Day After Tomorrow was so appallingly bad, it was that that prompted me to become a more public scientist”? What could an innocent blockbuster movie have done to deserve such harsh criticisms?

A New Ice Age?

The Day After Tomorrow opens with a new scientific discovery by paleoclimatologist Jack Hall, played by Dennis Quaid. After a particularly harrowing trip to gather Antarctic ice cores, he discovers evidence of a previously unknown climate shift that occurred ten thousand years ago. Since the film is set in the early 2000s, and ice cores yielding hundreds of thousands of years of climate data have been studied extensively since the 1960s, it seems implausible that such a recent and dramatic global climatic event would have gone previously unnoticed by scientists. However, this misstep is excusable, because a brand new discovery is a vital element of many science fiction films.

Jack goes on to describe this ancient climate shift. As the world was coming out of the last glacial period, he explains, melting ice sheets added so much freshwater to the Atlantic Ocean that certain ocean circulation patterns shut down. Since thermohaline circulation is a major source of heat for the surfaces of continents, the globe was plunged back into an ice age. Jack’s portrayal of the event is surprisingly accurate: a sudden change in climate did occur around ten thousand years ago, and was most likely caused by the mechanisms he describes. To scientists, it is known as the Younger Dryas.

The world’s ascent out of the last ice age was not smooth and gradual; rather, it was punctuated by jumps in temperature coupled with abrupt returns to glacial conditions. The Younger Dryas – named after a species of flower whose pollen was preserved in ice cores during the event – was the last period of sudden cooling before the interglacial fully took over. Ice core data worldwide indicates a relatively rapid drop in global temperatures around eleven thousand years ago. The glacial conditions lasted for approximately a millennium until deglaciation resumed.

The leading hypothesis for the cause of the Younger Dryas involves a sudden influx of freshwater from the melting Laurentide Ice Sheet in North America into the Atlantic Ocean. This disruption to North Atlantic circulation likely caused North Atlantic deep water formation, a process which supplies vast amounts of heat to northern Europe, to shut down. Substantial regional cooling allowed the glaciers of Europe to expand. The ice reflected sunlight, which triggered further cooling through the ice-albedo feedback. However, the orbital changes which control glacial cycles eventually overpowered this feedback. Warming resumed, and the current interglacial period began.

While Jack Hall’s discussion of the Younger Dryas is broadly accurate, his projections for the future are far-fetched. He asserts that, since the most recent example of large-scale warming triggered glacial conditions, the global warming event currently underway will also cause an ice age. At a United Nations conference, he claims that this outcome is virtually certain and “only a matter of time”. Because it happened in the past, he reasons, it will definitely happen now. Jack seems to forget that every climate event is unique: while looking to the past can be useful to understand today’s climate system, it does not provide a perfect analogue upon which we can base predictions. Differences in continental arrangement, initial energy balance, and global ice cover, to name a few factors, guarantee that no two climate changes will develop identically.

Additionally, Jack’s statements regarding the plausibility of an imminent thermohaline shutdown due to global warming fly in the face of current scientific understanding. As the world continues to warm, and the Greenland ice sheet continues to melt, the North Atlantic circulation will probably slow down due to the added freshwater. The resulting cooling influence on parts of Europe will probably still be overwhelmed by warming due to greenhouse gases. However, a complete shutdown of North Atlantic deep water formation is extremely unlikely within this century. It’s unclear whether an eventual shutdown is even possible, largely because there is less land ice available to melt than there was during the Younger Dryas. If such an event did occur, it would take centuries and still would not cause an ice age – instead, it would simply cancel out some of the greenhouse warming that had already occurred. Cooling influences simply decrease the global energy balance by a certain amount from its initial value; they do not shift the climate into a predetermined state regardless of where it started.

Nevertheless, The Day After Tomorrow goes on to depict a complete shutdown of Atlantic thermohaline circulation in a matter of days, followed by a sudden descent into a global ice age that is spurred by physically impossible meteorological phenomena.

The Storm

Many questions about the Ice Ages remain, but the scientific community is fairly confident that the regular cycles of glacial and interglacial periods that occurred throughout the past three million years were initiated by changes in the Earth’s orbit and amplified by carbon cycle feedbacks. Although these orbital changes have been present since the Earth’s formation, they can only lead to an ice age if sufficient land mass is present at high latitudes, as has been the case in recent times. When a glacial period begins, changes in the spatial and temporal distribution of sunlight favour the growth of glaciers in the Northern Hemisphere. These glaciers reflect sunlight, which alters the energy balance of the planet. The resulting cooling decreases atmospheric concentrations of greenhouse gases, through mechanisms such as absorption by cold ocean waters and expansion of permafrost, which causes more cooling. When this complex web of feedbacks stabilizes, over tens of thousands of years, the average global temperature is several degrees lower and glaciers cover much of the Northern Hemisphere land mass.

The ice age in The Day After Tomorrow has a more outlandish origin. Following the thermohaline shutdown, a network of massive hurricane-shaped snowstorms, covering entire continents, deposits enough snow to reflect sunlight and create an ice age in a matter of days. As if that weren’t enough, the air at the eye of each storm is cold enough to freeze people instantly, placing the characters in mortal danger. Jack’s friend Terry Rapson, a climatologist from the UK, explains that cold air from the top of the troposphere is descending so quickly in the eye of each storm that it does not warm up as expected. He estimates that the air must be -150°F (approximately -100°C) or colder, since it is instantly freezing the fuel lines in helicopters.

There are two main problems with this description of the storm. Firstly, the tropopause (the highest and coldest part of the troposphere) averages -60°C, and nowhere does it reach -100°C. Secondly, the eye of a hurricane – and presumably of the hurricane-shaped snowstorms – has the lowest pressure of anywhere in the storm. This fundamental characteristic indicates that air should be rising in the eye of each snowstorm, not sinking down from the tropopause.

Later in the film, NASA scientist Janet Tokada is monitoring the storms using satellite data. She notes that temperature is decreasing within the storm “at a rate of 10 degrees per second”. Whether the measurement is in Fahrenheit or Celsius, this rate of change is implausible. In under a minute (which is likely less time than the satellite reading takes) the air would reach absolute zero, a hypothetical temperature at which all motion stops.

In conclusion, there are many problems with the storm system as presented in the film, only a few of which have been summarized here. One can rest assured that such a frightening meteorological phenomenon could not happen in the real world.

Sea Level Rise

Before the snowstorms begin, extreme weather events – from hurricanes to tornadoes to giant hailstones – ravage the globe. Thrown in with these disasters is rapid sea level rise. While global warming will raise sea levels, the changes are expected to be extremely gradual. Most recent estimates project a rise of 1-2 metres by 2100 and tens of metres in the centuries following. In contrast, The Day After Tomorrow shows the ocean rising by “25 feet in a matter of seconds” along the Atlantic coast of North America. This event is not due to a tsunami, nor the storm surge of a hurricane; it is assumed to be the result of the Greenland ice sheet melting.

As the film continues and an ice age begins, the sea level should fall. The reasons for this change are twofold: first, a drop in global temperatures causes ocean water to contract; second, glacier growth over the Northern Hemisphere locks up a great deal of ice that would otherwise be present as liquid water in the ocean. However, when astronauts are viewing the Earth from space near the end of the film, the coastlines of each continent are the same as today. They have not been altered by either the 25-foot rise due to warming or the even larger fall that cooling necessitates. Since no extra water was added to the Earth from space, maintaining sea level in this manner is physically impossible.

Climate Modelling

Since the Second World War, ever-increasing computer power has allowed climate scientists to develop mathematical models of the climate system. Since there aren’t multiple Earths on which to perform controlled climatic experiments, the scientific community has settled for virtual planets instead. When calibrated, tested, and used with caution, these global climate models can produce valuable projections of climate change over the next few centuries. Throughout The Day After Tomorrow, Jack and his colleagues rely on such models to predict how the storm system will develop. However, the film’s representation of climate modelling is inaccurate in many respects.

Firstly, Jack is attempting to predict the development of the storm over the next few months, which is impossible to model accurately using today’s technology. Weather models, which project initial atmospheric conditions into the future, are only reliable for a week or two: after this time, the chaotic nature of weather causes small rounding errors to completely change the outcome of the prediction. On the other hand, climate models are concerned with average values and boundary conditions over decades, which are not affected by the principles of chaos theory. Put another way, weather modelling is like predicting the outcome of a single dice roll based on how the dice was thrown; climate modelling is like predicting the net outcome of one hundred dice rolls based on how the dice is weighted. Jack’s inquiry, though, falls right between the two: he is predicting the exact behaviour of a weather system over a relatively long time scale. Until computers become vastly more precise and powerful, this exercise is completely unreliable.

Furthermore, the characters make seemingly arbitrary distinctions between “forecast models”, “paleoclimate models”, and “grid models”. In the real world, climate models are categorized by complexity, not by purpose. For example, GCMs (General Circulation Models) represent the most processes and typically have the highest resolutions, while EMICs (Earth System Models of Intermediate Complexity) include more approximations and run at lower resolutions. All types of climate models can be used for projections (a preferred term to “forecasts” because the outcomes of global warming are dependent on emissions scenarios), but are only given credence if they can accurately simulate paleoclimatic events such as glacial cycles. All models include a “grid”, which refers to the network of three-dimensional cells used to split the virtual Earth’s surface, atmosphere, and ocean into discrete blocks.

Nevertheless, Jack gets to work converting his “paleoclimate model” to a “forecast model” so he can predict the path of the storm. It is likely that this conversion involves building a new high-resolution grid and adding dozens of new climatic processes to the model, a task which would take months to years of work by a large team of scientists. However, Jack appears to have superhuman programming abilities: he writes all the code by himself in 24 hours!

When he has finished, he decides to get some rest until the simulation has finished running. In the real world, this would take at least a week, but Jack’s colleagues wake him up after just a few hours. Evidently, their lab has access to computing resources more powerful than anything known to science today. Then, Jack’s colleagues hand him “the results” on a single sheet of paper. Real climate model output comes in the form of terabytes of data tables, which can be converted to digital maps, animations, and time plots using special software. Jack’s model appeared to simply spit out a few numbers, and what these numbers may have referred to is beyond comprehension.

If The Day After Tomorrow was set several hundred years in the future, the modelling skill of climate scientists and the computer power available to them might be plausible. Indeed, it would be very exciting to be able to build, run, and analyse models as quickly and with as much accuracy as Jack and his colleagues can. Unfortunately, in the present day, the field of climate modelling works quite differently.

Conclusions

The list of serious scientific errors in The Day After Tomorrow is unacceptably long. The film depicts a sudden shutdown of thermohaline circulation due to global warming, an event that climate scientists say is extremely unlikely, and greatly exaggerates both the severity and the rate of the resulting cooling. When a new ice age begins in a matter of days, it isn’t caused by the well-known mechanisms that triggered glacial periods in the past – rather, massive storms with physically impossible characteristics radically alter atmospheric conditions. The melting Greenland ice sheet causes the oceans to rise at an inconceivable rate, but when the ice age begins, sea level does not fall as the laws of physics dictate it should. Finally, the film depicts the endeavour of science, particularly the field of climate modelling, in a curious and inaccurate manner.

It would not have been very difficult or expensive for the film’s writing team to hire a climatologist as a science advisor – in fact, given that the plot revolves around global warming, it seems strange that they did not do so. One can only hope that future blockbuster movies about climate change will be more rigorous with regards to scientific accuracy.

What Can One Person Do?

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.

“It’s Just a Natural Cycle”

My second rebuttal for Skeptical Science. Thanks to all the folks who helped to review it! Further suggestions are welcome, as always. -Kate

“What if global warming is just a natural cycle?” This argument is, perhaps, one of the most common raised by the average person, rather than someone who makes a career out of denying climate change. Cyclical variations in climate are well-known to the public; we all studied the ice ages in school. However, climate isn’t inherently cyclical.

A common misunderstanding of the climate system characterizes it like a pendulum. The planet will warm up to “cancel out” a previous period of cooling, spurred by some internal equilibrium. This view of the climate is incorrect. Internal variability will move energy between the ocean and the atmosphere, causing short-term warming and cooling of the surface in events such as El Nino and La Nina, and longer-term changes when similar cycles operate on decadal scales. However, internal forces do not cause climate change. Appreciable changes in climate are the result of changes in the energy balance of the Earth, which requires “external” forcings, such as changes in solar output, albedo, and atmospheric greenhouse gases. These forcings can be cyclical, as they are in the ice ages, but they can come in different shapes entirely.

For this reason, “it’s just a natural cycle” is a bit of a cop-out argument. The Earth doesn’t warm up because it feels like it. It warms up because something forces it to. Scientists keep track of natural forcings, but the observed warming of the planet over the second half of the 20th century can only be explained by adding in anthropogenic radiative forcings, namely increases in greenhouse gases such as carbon dioxide.

Of course, it’s always possible that some natural cycle exists, unknown to scientists and their instruments, that is currently causing the planet to warm. There’s always a chance that we could be totally wrong. This omnipresent fact of science is called irreducible uncertainty, because it can never be entirely eliminated. However, it’s very unlikely that such a cycle exists.

Firstly, the hypothetical natural cycle would have to explain the observed “fingerprints” of greenhouse gas-induced warming. Even if, for the sake of argument, we were to discount the direct measurements showing an increased greenhouse effect, other lines of evidence point to anthropogenic causes. For example, the troposphere (the lowest part of the atmosphere) is warming, but the levels above, from the stratosphere up, are cooling, as less radiation is escaping out to space. This rules out cycles related to the Sun, as solar influences would warm the entire atmosphere in a uniform fashion. The only explanation that makes sense is greenhouse gases.

What about an internal cycle, perhaps from volcanoes or the ocean, that releases massive amounts of greenhouse gases? This wouldn’t make sense either, not only because scientists keep track of volcanic and oceanic emissions of CO2 and know that they are small compared to anthropogenic emissions, but also because CO2 from fossil fuels has its own fingerprints. Its isotopic signature is depleted in the carbon-13 isotope, which explains why the atmospheric ratio of carbon-12 to carbon-13 has been going down as anthropogenic carbon dioxide goes up. Additionally, atmospheric oxygen (O2) is decreasing at the same rate that CO2 is increasing, because oxygen is consumed when fossil fuels combust.

A natural cycle that fits all these fingerprints is nearly unfathomable. However, that’s not all the cycle would have to explain. It would also have to tell us why anthropogenic greenhouse gases are not having an effect. Either a century of basic physics and chemistry studying the radiative properties of greenhouse gases would have to be proven wrong, or the natural cycle would have to be unbelievably complex to prevent such dramatic anthropogenic emissions from warming the planet.

It is indeed possible that multidecadal climate variabilityespecially cycles originating in the Atlantic, could be contributing to recent warming, particularly in the Arctic. However, the amplitude of the cycles simply can’t explain the observed temperature change. Internal variability has always been superimposed on top of global surface temperature trends, but the magnitude – as well as the fingerprints – of current warming clearly indicates that anthropogenic greenhouse gases are the dominant factor.

Despite all these lines of evidence, many known climatic cycles are often trumpeted to be the real cause, on the Internet and in the media. Many of these cycles have been debunked on Skeptical Science, and all of them either aren’t in the warming phases, don’t fit the fingerprints, or both.

For example, we are warming far too fast to be coming out of the last ice age, and the Milankovitch cycles that drive glaciation show that we should be, in fact, very slowly going into a new ice age (but anthropogenic warming is virtually certain to offset that influence).

The “1500-year cycle” that S. Fred Singer attributes warming to is, in fact, a change in distribution of thermal energy between the poles, not a net increase in global temperature, which is what we observe now.

The Little Ice Age following the Medieval Warm Period ended due to a slight increase in solar output (changes in both thermohaline circulation and volcanic activity also contributed), but that increase has since reversed, and global temperature and solar activity are now going in opposite directions. This also explains why the 11-year solar cycle could not be causing global warming.

ENSO (El Nino Southern Oscillation) and PDO (Pacific Decadal Oscillation) help to explain short-term variations, but have no long-term trend, warming or otherwise. Additionally, these cycles simply move thermal energy between the ocean and the atmosphere, and do not change the energy balance of the Earth.

As we can see, “it’s just a natural cycle” isn’t just a cop-out argument – it’s something that scientists have considered, studied, and ruled out long before you and I even knew what global warming was.

Stephen Schneider – Rest in Peace

Yesterday the world lost a great man, a gifted scientist, and a wonderful communicator. Stephen Schneider has died unexpectedly at the age of 65.

Ironically, after battling with a rare form of lymphoma and winning, Dr. Schneider succumbed to a heart attack as his plane landed in London yesterday morning. He was on his way home from a conference in Sweden.

To say that Stephen Schneider was a role model for scientists and science communicators would be an understatement. He was a pioneer in the field of climate modelling, and contributed greatly to our understanding of aerosols and their radiative forcing. However, he also fought tirelessly for public understanding of climate change. For more than thirty years, he epitomized science communication through books, interviews, appearances in documentaries, and online essays. I’m sure I’m not the only person who, after reading and listening to his contributions, often thought, “There, that’s it….that’s exactly what I’ve been trying to put into words.”

Despite death threats, hate mail, and out-of-context attacks on his integrity that persisted for decades, Stephen Schneider persisted in his communication. He understood the importance of public discussion and understanding on climate change, and nobody was better qualified than him to talk about it. He is the kind of scientist I want to become. As Ben Santer wrote in a touching eulogy on RealClimate,

Some scientists have exceptional talents in pure research…Others have strengths in communicating complex scientific issues to non-scientists. It is rare to find scientists who combine these talents. Steve Schneider was such a man…[He] did for climate science what Carl Sagan did for astronomy.

My interactions with Dr. Schneider were brief, but I was amazed at how responsive and supportive he was. I emailed him when I was researching an early story on a certain infamous quote, and he responded with links and further context, despite surely being asked about this quote on a weekly basis. A year or so later, I wrote to him again to tell him how much I enjoyed his most recent book, and he replied to thank me, commend me on my career choice, and invite me to email him for advice whenever I needed it. For a scientist who is at the top of his field and continually approached by the media, he sure makes time for students and those who are interested in his work.

As Ben Santer said, we must honor Stephen Schneider by continuing the work he left for us: understanding the complexities of the climate system, communicating what we already know to the public, fighting back against those who seek to misrepresent the science, and – above all – ensuring that our future is secure on this beautiful and fragile planet.

My condolences to his family, friends, and colleagues. He will truly be missed, and his contributions will not be forgotten.

Snowball Earth

Of all the books I have read about climate change, Snowball Earth, by Gabrielle Walker, is definitely one of the best – and it’s not even about the current climate change.

Part of what makes it so good is the style of writing. As the Los Angeles Times said about her later book, An Ocean of Air, “Walker has a Ph.D. in chemistry, but she writes like a poet.” And, indeed, after an education at Cambridge, Walker has spent most of her career as a science journalist. It’s sort of sad that this doesn’t happen more often. Usually, those who understand a subject best are not the ones who communicate it. Walker is the exception to this rule.

Take, for example, this passage about the history of life on Earth:

Stretch your arms out wide to encompass all the time on Earth. Let’s say that time runs from left to right, so Earth was born at the tip of the middle finger on your left hand. Slime arose just before your left elbow and ruled for the remaining length of your left arm, across to the right, past your right shoulder, your right elbow, on down your forearm, and eventually ceded somewhere around your right wrist. For sheer Earth-gripping longevity, nothing else comes close. The dinosaurs reigned for barely a finger’s length. And a judicious swipe of a nail file on the middle finger of your right hand would wipe out the whole of human history.

Another impressive aspect of Walker’s writing is her characterization. Wacky, stubborn, and exuberant scientists are brought to life. Instead of just hearing about their work and accomplishments, you feel like you’re getting to know them as people. She writes about arguing scientists particularly well. Arguing scientists are so much fun to read about – that’s one reason I loved The Lost World by Arthur Conan Doyle.

However, the best part of this book, by far, is the subject matter. The theory of Snowball Earth is possibly the most awesome thing I have ever heard about. Here’s how the story goes:

From what paleontologists can see preserved in fossils, complex life arose at a very specific point in prehistory: the end of the Precambrian. For several billion years before that, the only thing that lived on Earth was unicellular goop. But then, suddenly, all at once, complex organisms burst onto the evolutionary stage.

Something must have caused this dramatic appearance, and a series of scientists from the 1940s on – most prominently, Paul Hoffman – likely have discovered what. At the end of the Precambrian, there are signs of ice in rocks all over the world – scratches, rock deposits, everything that led Agassiz to discover the ice ages.

Because plate tectonics moves everything around so much, though, rocks were not necessarily formed at the location they sit today. Their magnetic field is what discloses their birthplace. Tiny bits of magnetic material, such as iron, line their field up with the Earth’s. The Earth’s magnetic field is perpendicular to the surface at the poles and parallel to the surface at the Equator, like this:

So, if a rock’s magnetic field is vertical, it was formed at the poles. If it is horizontal, it was formed at the equator. Incredibly, scientists found Precambrian rocks, with signs of ice, with horizontal magnetic fields. During that period of prehistory, the equator was covered in ice – and, therefore, the whole planet, because it’s not really possible to freeze the equator without freezing all the other latitudes too.

The scientists determined that, for several instances on the Precambrian, the continents were arranged in a way that was very conducive to ice-albedo feedback. With the smallest trigger, ice from the poles would creep across the temperature zones and meet at the equator. Frozen oceans, frozen land, the whole bit.

And now CO2 comes into the story. Volcanic eruptions naturally release carbon dioxide, but the amount is so small that the oceans have no trouble soaking them up – unless they’re frozen on the surface and cut off from the air. CO2 would gradually build up, in that case, and millions of years later, the greenhouse effect would be so strong that all the ice would melt and the planet would plunge into a state referred to as Hothouse Earth. Then the oceans would start absorbing all the extra CO2, and ice would reappear at the poles, and the cycle would begin again.

Many scientists believe that these Precambrian cycles of extreme heat and extreme cold provided such a strong pressure on organisms that natural selection was pushed to new boundaries. Complex life had an advantage in these extreme conditions, and it flourished. The most catastrophic climatic event our planet has ever experienced, in our knowledge, was what led to the evolution of multicellular organisms, and eventually, us.

It makes me feel very small, the same way that attempting to comprehend the vastness of the universe makes me feel very small. The life we see all around us only exists because of a series of coincidences. Human beings, one of the youngest of the millions of animal species that have ever existed, are alive because of continental drift lining things up in the right way. And who knows what would have happened if things had been slightly different?

The Discovery of Global Warming

A common remark I make about climate change books I like is that “it wasn’t like a textbook”. I like non-fiction books that I can carry around and read cover-to-cover just like I would a novel. I like them to draw me in and catch my interest as if they were a suspenseful PD James or just a comfortable Maeve Binchy.

The Discovery of Global Warming, by Spencer Weart, had all of these qualities and more: It contained as much information as a textbook, even if it didn’t read like one. That, I think, is the benefit of science history. It can be written in a way that is compelling as fiction, but it’s all true.

I think I will place this book near the top of my list of resources for concerned citizens who are looking for more information on climate change. It is so helpful because, instead of saying “scientists are confident that humans are causing the Earth to warm”, it traces back through history and follows this discovery all the way through, from Fourier to the AR4. We see the top of the credibility spectrum in action, and examine exactly where the conclusions of the scientific community came from.

There are lots of great details in this book to sink your teeth into. How did the Cold War pave the way for much of our knowledge about the atmosphere? Why does chaos theory apply to weather models much more than climate models? And, of course, my very favourite – the 1970s aerosol debate. How did scientists realize that the warming force of greenhouse gases would overpower the cooling force of aerosols, long before the warming was actually observed?

All of this is written in an incredibly elegant and engaging tone. Weart’s style of writing somehow reminds me of Sir Arthur Conan Doyle in The Lost World – succinct characterization, unintended (or just well-hidden) satire, a calm detachment from the story that somehow makes it all the more fascinating.

I read the “Revised and Expanded Edition”, so I’m not sure if all editions of The Discovery of Global Warming contain all the extras in the back: a timeline, an index, and a chapter entitled “Reflections” that is full of Weart’s musings about risk management and science communication. “Unlike, say, the orbits of planets,” he writes, “the climate in the future actually does depend in part on what we think about it. For what we think will determine what we do.”

A tangible alternative to the more comprehensive online version (really, who wants to read a book by navigating a web of links and scrolling through chapters on a computer screen?), The Discovery of Global Warming is worth every cent, and every minute of your time it takes to read it. I look forward to future volumes as this story continues to unfold.