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October 28, 2008

Wedges
This is not about cheese (although Beyond Cheese would be a great name for a blog). But the chart that illustrates the wedges I'm talking about is not quite so yummy. I'm thinking about wedges today after reading this piece by Bryan Walsh on Time.com. Apparently, even MIT grad students aren't clear on the climate challenge before us:
In a paper that came out Oct. 23 in Science, John Sterman -- a professor at Massachusetts Institute of Technology's (MIT) Sloan School of Management -- wrote about asking 212 MIT grad students to give a rough idea of how much governments need to reduce global greenhouse gas emissions by to eventually stop the increase in the concentration of carbon in the atmosphere. These students had training in science, technology, mathematics and economics at one of the best schools in the world -- they are probably a lot smarter than you or me. Yet 84% of Sterman's subjects got the question wrong, greatly underestimating the degree to which greenhouse gas emissions need to fall.
It's no wonder then that Walsh reports that 54% of Americans want to adopt a "wait-and-see" approach to climate change. The problem is that there's no "visible" crisis on the one hand and on the other it's had to conceive of the scale of the challenge. Of course, if we wait until the real catastrophes start happening, it will be too late.

Walker has a nice summation of the problem:
Before the industrial age, the concentration was about 280 parts per million (p.p.m.) of carbon in the atmosphere. After a few centuries of burning coal, oil and other fossil fuels, we've raised that concentration to 387 p.p.m., and it continues to rise by about 2 p.p.m. every year. Many scientists believe that we need to at least stabilize carbon concentrations at 450 p.p.m. to ensure that global temperatures don't increase more than about 2 degrees Celsius above the pre-industrial level. To do that, we need to reduce global carbon emissions (which hit about 10 billion tons last year) until they are equal to or less than the amount of carbon sequestered by the oceans and plant life (which removed about 4.8 billion tons of carbon last year). It's just like water in a bathtub -- unless more water is draining out than flowing in from the tap, eventually the bathtub will overflow.
And it gets worse. Recent research suggests that positive feedback loops in the carbon cycle will act like a tripwire. If we get much above 550ppm of carbon in the atmosphere, we will then jump up to 800 or 1000ppm in a short period of time regardless of how much we cut our emissions. CAP's Joe Romm explains why this is doubleplus ungood:

At 800 to 1000 ppm, the world faces multiple miseries, including:

  1. Sea level rise of 80 feet to 250 feet at a rate of 6 inches a decade (or more).
  2. Desertification of one third the planet and drought over half the planet, plus the loss of all inland glaciers.
  3. More than 70% of all species going extinct, plus extreme ocean acidification.
That's plenty scary. But honestly all those ppms make my head hurt. And what's billions of tons of carbon anyway? How on earth do we figure out what we actually have to do!!

Well, I'm glad I asked that question. Romm and others have picked up on work done by two Princeton University professors, Stephen Pacala and Robert Socolow. These two scientists started with the graph below of the increase in carbon over time and overlaid a baseline at which the climate was stable (and now you'll realize why I started with cheese).
From there, they took that yellow area and split it into sections, which they dubbed "stabilization wedges" and it looks like this:
The idea is that each wedge represents what carbon concentration growth would look like if you took 1 billion tons of carbon (aka a gigaton of carbon or GtC) out of the atmosphere over the period from 2004 to 2050 - by which time our goose will have been collectively cooked. So, 7 wedges to salvation. That's 7 billion tons of carbon out of the atmosphere between "now" and 2050. Check.

Still with me? Well, there's a problem. This work was originally done back in 2004 and things have changed. Estimates now are that we need 14 wedges (i.e. to start on a path to remove 14 billion tons of carbon by 2050), not the 7 Pacala and Socolow suggested we'd need, to keep a stable climate, i.e. double the reduction over a little less time.

But we're still at a level of abstraction that's not really going to help anyone. What's a wedge in real terms? After all, this is supposed to help us grasp the scale of the problem. Well, once again, we turn to Joe Romm and his "14 wedge solution"
  • 1 wedge of vehicle efficiency -- all cars 60 mpg, with no increase in miles traveled per vehicle.
  • 1 of wind for power -- one million large (2 MW peak) wind turbines
  • 1 of wind for vehicles --another 2000 GW wind. Most cars must be plug-in hybrids or pure electric vehicles.
  • 3 of concentrated solar thermal -- ~5000 GW peak.
  • 3 of efficiency -- one each for buildings, industry, and cogeneration/heat-recovery for a total of 15 to 20 million GW-hrs.
  • 1 of coal with carbon capture and storage -- 800 GW of coal with CCS
  • 1 of nuclear power -- 700 GW plus 10 Yucca mountains for storage
  • 1 of solar photovoltaics -- 2000 GW peak [or less PV and some geothermal, tidal, and ocean thermal]
  • 1 of cellulosic biofuels -- using one-sixth of the world's cropland [or less land if yields significantly increase or algae-to-biofuels proves commercial at large scale].
  • 2 of forestry -- End all tropical deforestation. Plant new trees over an area the size of the continental U.S.
  • 1 of soils -- Apply no-till farming to all existing croplands.
So that's one theory of what it would take to "solve" climate change. And here's the kicker. If we don't start by 2012 it will be too late. Are you laughing or crying? I can't tell. The point of this post was not, I'm afraid, to make anyone happy. Because it turns out the problem is bigger and scarier than anyone but the climate scientists seem to understand. Which is why I needed to scare you. Perhaps you're ready for that cheese now?

Photo by Steel Wool used under CC license


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Blogger trayf said...

Even the 450 ppm target might be optimistic, which is why Bill McKibben's new group 350.org advocates for getting it back down to that number. Same idea, but bigger wedges.

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