Graph(s) of the week: Carbon emissions, measured in absolute yearly amounts and per capita levels, from the web site of CDIAC (Carbon dioxide Information Analysis Center), perhaps the most interesting and important US government site that not enough energy and environmental geeks know about. One of these graphs is terrifying, and I’m willing to bet that it’s not the one most of you would have picked after a quick glance (at least without this spoiler).
Please note that the values graphed below are carbon, not CO2. I normally try to stick to talking about CO2, but the critical detail is the shape of the curves. Mentally scale the lines in these graphs upwards by a factor of 3.67, if you’re so inclined.
First up is annual global carbon emissions:
(Click on the graph to see a slightly larger version in a new window.)
Notice that this is not a plot of cumulative emissions, but yearly emissions. In other words, the steep slope of the curve is not an indication of how quickly the running total of carbon that humanity has poured into the atmosphere is rising. It’s a measure of how quickly our annual emissions have risen since roughly the beginning of the Industrial Revolution.
Next on our graphical hit parade is per capita carbon emissions:
(Click on the graph to see a slightly larger version in a new window.)
Worldwide per capita carbon emissions have remained relatively flat since the mid-1970′s. So surely the “terrifying” graph is the total, right? Well, no. I would argue that the per capita graph is the scary one, for a couple of very basic reasons[1]:
First, the world population is still rising, a lot. We’re currently in the neighborhood of 6.8 billion people[2], and the most common prediction I’ve seen is that world population will top out at around 9 billion in 2050. Call it an increase of one third over today’s level. If nothing else changes, meaning the mix of people in different economic groups and following various consumption patterns, the carbon intensity of the things those people do, etc., then we’re looking at a staggering increase in carbon emissions, from today’s 8 billion metric tons/year to about 10.6 billion metric tons/year, in a span of 41 years, less than the lifetime of a coal or nuclear power plant, and well within the lifetime of most people reading this site.
In other words, the per capita graph will have to decline noticeably from its current plateau.
How do we avoid that level of increase in carbon emissions? Some combination of fewer people and less carbon per person. That’s the easy, quick, and almost useless answer, given how difficult it will be to get the yearly emissions down enough to keep the atmospheric level low enough to avoid catastrophic consequences.
Second, the one key assumption I made above–”if nothing else changes”, a.k.a. ceteris paribus isn’t true. The worldwide CO2 emissions per person will rise unless we take heroic actions to prevent them. The issue is those oft-mentioned “developing countries”, most conspicuously China and India, two countries developing and growing their middle classes at an astonishing rate. And those middle classes are showing a marked tendency in their consumption patterns–more meat on their plates, more electrons in their homes, more motor vehicles–that sound very much like European and, dare I say it, American consumers.
Look closer at that per capita line. Not only is it not declining, it started to turn up around 2000. And that’s the value we multiply by the (rising) world population to arrive at the total yearly emissions. In other words, humanity faces the dual chores of de-carbonizing the “developed” nations as well as keeping a lot of the future growth in “developing” countries from carbonzing in the first place (and de-carbonizing some that’s already happened).
Terrified yet?
[1] Careful readers will no doubt remember that I’ve argued against being too enamored of per capita or per GDP dollar numbers, because Earth’s climate doesn’t know or care about such derived statistics. It responds to aggregates–how much warming is triggered by the total level of greenhouse gases in the atmosphere, how much cooling is triggered by aerosols, etc. This is one time where I think the per capita number yields an unusually large amount of information, in the proper context.
[2] See the US Census Bureau’s population clock for a value of around 6.77 billion, and this one for a value of around 6.92 billion. For more information about the world population that you probably need or want to know, see Wikipedia’s entry.
