Friday, July 13, 2012

The Basic Science Of Climate Change Is Undeniable

It’s not hard to have heat on the brain this summer, especially here in the United States. Since the government began keeping records in 1895, this June was the hottest June – 2 degrees Fahrenheit above the 20th Century average. The past six months have been the hottest first half of the year on record since 1895, and for the 12 month period ending June 30th, it was also the hottest year on record since the United States began keeping records. Given that this followed a record warm winter and that the last decade has seen a tie for the hottest year on record, climate change has once again become a topic of debate. That being the case, I thought I might review what’s often lost in discussions of climate change: the basic chemistry that underlies what we know about how it works.
The science of climate change is almost two centuries old. To the best of our knowledge, it began with Joseph Fourier, who first noted in the 1820s that, given Newton’s laws of cooling, the Earth should be much colder than it actually is given its distance from the Sun. He developed a number of hypotheses for the origin of the extra heat, one of which was the possibility that the atmosphere itself traps the heat that makes life possible. Other scientists built on Fourier’s work, notably John Tyndall, who in the 1850s  not only demonstrated that gasses trapped heat, but also determined how well each of those gasses trapped heat. Carbon dioxide was one of those gasses that traps heat well. The main components of the atmosphere – oxygen and nitrogen – don’t trap heat well.
This simple fact – that increasing carbon dioxide concentration in a gaseous mixture will increase temperatures – is undeniable. It is something that you can demonstrate at your own house for a couple of bucks worth of materials. This video provides one such setup:
At a basic level, we can demonstrate that carbon dioxide concentration impacts temperatures. (This is also true of the other primary greenhouse gasses, including water vapor and methane.) It doesn’t take much to go from there and predict that rising carbon dioxide levels in the atmosphere will also lead to increased temperatures. In fact, this hypothesis wasfirst proposed in 1896 by Svante Arrhenius, who would go on to win the Nobel Prize in 1903. In Arrhenius’ paper, he discussed how variations in carbon dioxide concentration in the atmosphere must be naturally variable, and that variations in carbon dioxide are what lead to excessively warm and cold periods in the Earth’s history. Many of Arrhenius’ assumptions have since been validated, and even his mathematical predictions weren’t too far off.
Arrhenius’ paper wasn’t a one-off, either. It was the product of over five decades worth of work, in which he engaged with furious debates with other scientists who doubted his claims, leading to investigations of the climate effects of ice, the oceans, trees, industrial pollution and more. Despite Arrhenius’ diligent and thorough work, however, it was still mostly ignored until the 1950s. After that period, though, it became increasingly apparent that carbon dioxide concentrations were going to be a problem for the climate. In 1965, a government committee warned President Johnson of the dangers of global warming. 10 years later, Wally Broecker published his paper “Are we on the brink of a pronounced global warming?” in Science. You can read a great summary of the importance of that paper here.
It’s true that climate is extremely complicated, with a number of variable factors that can influence temperature and climate. There’s even quite a few of those factors that we don’t understand completely. Despite that, though, the simple fact underlying climate change is the same whether you’re talking a 2-liter bottle or the Earth’s atmosphere: if you add carbon dioxide to a mixture of gasses, the mixture will trap more heat.
What Arrenhius predicted in 1896 is basically what we’ve seen: since the beginning of the industrial revolution, carbon dioxide emissions have steadily increased. You can see that increase in the chart below from NASA/NOAA, which looks at carbon dioxide concentrations for the past 650,000 years:
Also since that time, average global temperatures have been increasing, as you can see from this chart from NASA’s Goddard Institute for Space Studies:
In the end, everything about climate science boils down to one simple fact: all else being equal, increasing the concentration of carbon dioxide in a mixture of gasses will cause the mixture to absorb more heat.
That is the simple, undeniable fact that underlies the science of climate change.

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