Beware of Movies! Climate Change

The Beware of Movies! series is meant to point out some of the scientific inaccuracies of popular movies, specifically in points related to the geological sciences.

This post will point out the major inaccuracies portrayed in movies about climate change, and how it would affect the Earth.

Climate change is a sensitive topic. It’s become politically charged. It’s now taboo to talk about it in polite company. I’m not here to incite riots. I have my opinions that, though I won’t state them explicitly, they’ll probably be obvious. My objective here is to talk about how we understand climate change, how we can infer that it is happening. I want to demystify all the numbers and data points and graphics that we’re bombarded with every day.

There have been a few movies that have dealt with the topic of climate change. An Inconvenient Truth is a documentary about climate change, and it focuses very much on the likelihood that the Earth is warming rapidly and that we’re in a lot of trouble. The Day After Tomorrow is fictional, but deals with one possible outcome of global warming – a renewed ice age.

Evidence for Global Warming

You’ve heard about it: The Hockey Stick. It’s a depiction of global temperatures over the last few thousand years. The graph is relatively intuitive. Warmer times are higher (making bumps or peaks) on the graph then cooler time, which make little troughs. Where it comes from is a little complex. If you look closely at the graph, you see that the vertical axis isn’t just temperature, but a temperature anomaly. What that means, exactly, is a little too complex for this little post. You can read here to learn more about what the anomaly is. But, at a first pass, up equals warmer is sufficient.

The Hockey Stick

When we look at the Hockey Stick, we see some bumps. Some warmer times, and some cooler times. What really stands out is that in the last 50 years or so, we see a dramatic increase in temperature to things warmer than they’ve ever been. If you eyeball a line through the entire pattern, it seems basically flat, except for that last bit. There’s a sharp turn, and our little line looks a lot like a hockey stick.

A Hockey Stick

Is the Hockey Stick real?

One of the greatest topics of debate is whether or not the Hockey Stick is ‘real’ or just a statistical accident, a reflection of poor thermometry, or just part of the Earth’s natural cycles.

If you go to this post, the statistical argument is discussed. The take-home message is that even with error bars on the individual data points making up the Hockey Stick, the pattern still exists.

Error Bars: The term ‘error’ carries the connotation of being ‘wrong.’ In science, however, error is a measure of correctness. It’s a measure of precision. Error takes into account the fact that one instrument might read a little differently than another, or that one scientist might record the data differently. It takes into account all the little things that can cause a single recorded number to be a little less exact. Time of day, weather, sunlight are all things that can cause a thermometer to read a temperature slightly differently than the exact temperature. When you’re compiling data from several sources, you have to account for the variation from place to place. All of this is included in the error bar. Error bars on the Hockey Stick are just saying that “the temperature is this number, or maybe a little warmer or cooler.”

Well, maybe the problem is that our thermometers don’t work.

Knock, knock.
Who’s there?
Arthur.
Arthur who?
Arthur Mometer is broken.
 

The most recent part of the Hockey Stick – the last 50 years especially – is understood from direct measurements of temperature using thermometers. We look outside. The thermometer says 35 degrees. We write that down. There have been thermometers around for quite a while keeping track of air temperatures. We gather that data from sites all over the world and compile it. But you can have two thermometers side by side and they’ll read slightly different temperatures. This variation between thermometers is what goes into the error bars.

The Hockey Stick goes back in time to periods much older than the first thermometer, however. We use ‘paleothermometers’ to estimate ancient temperature. Measurements of ancient temperature depend on geochemical methods. (Read more about them here [Sorry, post isn’t written yet. Bad Penny].) Certain atmospheric chemicals vary according to temperature and are then included in the rock and the ice record. In fact, much we know about the Earth’s recent climatic history comes from ice cores in the Arctic and the Antarctic. There are three sources of error (or variation) in using geochemical methods to get at ancient temperature.

1) You have to measure the abundance of certain compounds, which itself isn’t exact. They are in very small quantities and therefore hard to measure.

2) The relationship between the abundance of the compound and ancient temperature has it’s own error bars. It’s not a perfect relationship, though it is pretty good.

3) The age of the ice or rock that you’re sampling might also not be exactly known. With rocks, you’d probably use radiocarbon dating to assign an age. With ice, it’s slightly easier. You need only count layers of ice, one for each year. Just hope you don’t lose count!

There’s some fairly large error bars that go along with the paleothermometry methods. Maybe paleothermometers don’t work at all. To the best of our understanding, they do work, and fairly accurately, and the Hockey Stick still exists, even when we account for all the error in our method.

Most are aware that the Earth has gone through several cycles of glaciation. This pattern is dictated by how the Earth spins on its axis and how it revolves around the sun (called orbital cycles). Some argue that the current warming trend is nothing but part of this cycle. Unfortunately, if you actually look at the orbital cycles, we should be getting cooler rather than warmer.

What could cause the Hockey Stick?

Well, if it’s not just bad statistics, bad data, or part of a natural cycle, what could be causing the warming? Greenhouse gasses are the most likely cause. Gasses like carbon dioxide and methane in the atmosphere are known to cause warming. They do this by absorbing and emitting heat, rather than letting heat just escape into space.

The argument is that these greenhouse gasses have increased in Earth’s atmosphere due to the burning of fossil fuels like coal and oil. We do know that carbon dioxide and methane are greenhouse gasses. We do know that burning fossil fuels emits carbon dioxide and methane. And we do burn a lot of fossil fuels. But this isn’t about trying to place blame. What’s more important is to find out if carbon dioxide and methane in the Earth’s atmosphere has increased, especially during the last 50 years or so.

We do have instrumental records of atmospheric carbon dioxide over the last 50 years, and we have seen a marked increase. But what about before then? Before the industrial revolution? Again, we can look to ice cores. Ice tends to retain little bubbles of air when it first forms. This air can be extracted and the concentration of carbon dioxide can be measured. As it happens, carbon dioxide concentrations were relatively constant until the 1800’s when it began a rapid increase. In fact, if you look at ice core records going back 400,000 years, there’s almost a perfect match between atmospheric carbon dioxide concentration and global temperature.

Carbon dioxide and temperature in Earth’s recent history.

 

So what does this mean?

This brings us back to movies. What does global warming and climate change mean. Oddly, the movie The Day After Tomorrow gets a lot of it right. The melting of the ice caps will cause sea level to rise. The melting could also upset the ocean’s circulation patterns, which can really, really screw up local climate. Hey, Europe is warm because of ocean currents.

Does this meant that it’s possible that global warming could plunge us into a new ice age? I don’t know. Is the Arctic going to become tropical? Well, it is pretty warm now. What the future holds, we don’t know. But it’s going to be different.

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