175 pounds

(That's not the amount of CO₂ you emit each and every day, but it might just be the amount you're responsible for.)

One of the challenges with getting people (including, but by no means limited to, students) to really believe in the impact of greenhouse gases is that the one everybody talks about -- the one that stands as a proxy for all the others -- is generally thought of as odorless, colorless, almost massless.  Methane you can think of as swamp gas, so it's easy to envision a damp, smelly substance hanging low in sumpy places and occasionally glowing after dark.  Nitrous is easy to think of as the stuff that makes you laugh or that will make your car's engine run REALLY fast.  But carbon dioxide -- how does anyone think about carbon dioxide?  It's invisible.  Almost intangible.  You can comprehend carbon dioxide in your mind, but it's hard to really believe it in your gut.  So it's hard to really commit to the idea that CO₂ has enough substance to be dangerous.

We need to do something about that.  And I think we just got the data to do it with.

King County, in the state of Washington, just did us all a favor.  With the help of the Stockholm Environment Institute, they conducted a laborious study to estimate the GHG emissions county residents are responsible for.  Not just the emissions which arise from the county itself and the activities therein, but the emissions created by county residents' activities and consumption.  If you are what you eat, then you emit what you consume (and I don't mean just food).

The SEI's estimate for King County, based on the year 2008, is 54.99 million metric tons of CO₂ equivalent emissions.  Convert to pounds and divide by a population of 1.88 million, and that's almost 64,500 pounds for every resident.  Divide by 366 (2008 was a leap year) and unless the back of my envelope is lying to me, it comes to a bit over 175 pounds.  Per person.  Each and every day.

That's a lot higher than other per-capita daily estimates I've seen, including King County's previous efforts (which already attempted to reflect a broader scope than any campus GHG inventory to my knowledge).  The reason is simple -- some 62% of the emissions for which each of us bears responsibility are generated by the creation (resource extraction, transportation, manufacturing, packaging) of the goods we use, not by how we use those goods.  And (as anyone looking at international balance of trade can tell you), the stuff we use is generally manufactured and grown a long distance from where we use it. 

The most common way to do GHG emissions estimation (because, while it's not especially easy, it's far easier than all the other ways) is to estimate the amount of gas emitted from a particular geographic area, or directly and almost-directly by a defined population.  What gets really hard (and what the King County study has done better than anything else I've seen) is estimating the amount of emission that is embodied in (because it results from the processes used to make) the products we use every day.

If you just stop to think about it, the reason China's GHG emissions are now greater than those from the USA is not because of the consumption patterns of the Chinese people.  Those emissions are the more-or-less-direct result of purchase decisions made in the USA, and Canada, and Europe, and Australia and Japan, and lots of other countries.  In a sense, the Chinese people couldn't eliminate those emissions even if they decided to.  The most they could do would be to relocate those emissions (by relocating the manufacturing jobs which directly create them) to other countries.  Inventorying GHG emissions by geographic area makes little sense in the greater scheme of things.  The vast majority of anthropogenic emissions aren't created by geographic space -- they're created by human consumption.  It's largely by changing consumption patterns that the emissions can be reduced significantly.  In fact, by conducting geographically-specific GHG inventories, we (all of us sustainability folks, myself included) have been muddying the waters.  And I don't mean Puget Sound.

Anyway, the good news is that I now have a number, and data to back the number up.  The amount of CO₂ equivalent emission each person in the USA is responsible for on a daily basis.  (All right, King County, WA, isn't truly representative of the USA as a whole.  It's more affluent than most counties, so one could make the case that product consumption is higher there.  But it's not all that much more affluent than the Backboro area, and I suspect it's not all that much more affluent than the counties where many colleges and universities are located.  Also, it has higher population density, better public transit, and milder weather than a lot of counties -- all of which factors moderate the effects of any presumed above-average product consumption.)

175 pounds.  I can't wait.  But I can weight -- I can put together a 175-pound barbell.  Just the sight of it (football players aside) should be enough to get most students' attention.

Especially when I point out that there's another 175 pounds coming tomorrow.  And the day after.  And the day after that.