I wonder if we’re making an enormous mistake in talking about CO2 the way we have–”there’s 385 parts per million of it in the air”, “the world emits 30 billion metric tons of it every year”, “we have to keep the atmospheric level of CO2 below 550 or 450 or 350 ppm”, etc. The problem is that these concepts are far too abstract for the average consumer and voter to grasp intuitively. Who the heck measures things in ppm or gigantic, context-free flows like 30 billion metric tons per year? Aside from climate scientists, policy makers working on climate legislation, and energy and environmental geeks, no one.
In this post I’ll try to provide some context and an explanation of what I think could be a more effective way to communicate the ticking clock problem we face regarding our CO2 emissions and climate chaos it’s triggering. the CO2 Countdown Clock.
I recently wrote about the infamous 2°C number (see Two degrees of separation), as in that being the “guardrail” for how much global warming, compared to pre-industrial times, we can withstand without triggering “unacceptable” human impacts. My online detective work didn’t really yield a satisfying (to me) answer; either we somehow guessed right 20 years ago, before two decades of “it’s worse than we thought” news stormed into our field of view, or we overestimated the safe level of temperature change and have yet to adjust the guardrail in response to our enhanced (albeit still imperfect) understanding of how the planet’s climate system works and responds to major shocks, like the one we’ve been delivering to it since about 1750. (If you believe the latter, then it’s interesting to ask why we haven’t yet “officially” adjusted the number. Institutional momentum? Fear of the reaction if scientists tell the world we’re already cooked and just didn’t realize it until very recently?)[1]
Connecting the sequence from “this highly undesirable effect is happening in the world” to “what actions should we take about it” requires one more level of mapping, once we agree to accept 2°C as the right guardrail: How much do we need to reduce CO2 emissions to avoid violating that upper limit on warming?
The standard answer repeated endlessly here and everywhere else is that countries like the US need to reduce their CO2 emissions by 80% from 1990 levels by 2050. But where did that number come from? The explanation can be found in a book I reviewed in April, David Archer’s The Long Thaw (Book review: The Long Thaw). I will paraphrase and quote from pages 161 onward, with some comments inserted and emphasis added.
Archer explains that the trail begins with the value ΔT2x, which is “the eventual warming you’d get from doubling atmospheric CO2.” He then says:
The IPCC states a range of 2.5-4°C, with 95% confidence, for ΔT2x. A good middle-of-the-road value is 3°C. The time period of maximum CO2 concentration, the peak, will probably last a few centuries. Since it takes a few centuries for climate to fully respond to rising CO2, the warming that could be expected within that time frame is probably a bit less than the full equilibrium value represented by ΔT2x. Given the uncertainty in ΔT2x, it has been calculated that an atmospheric CO2 concentration of about 420 ppm would have a good chance of avoiding a warming of 2°C.
(A doubling of pre-industrial CO2 levels would bring us to around 550 ppm, which was considered “the” target for a while.)
Archer next points out that while there’s some uncertainty about exactly how much carbon that translates to (I assume because of varying rates of CO2 uptake by plants and the oceans as the atmospheric level of CO2 rises and other climate details change), a 420 ppm limit means a 600 billion ton limit for carbon in the form of CO2 (not 600 Gton of CO2) emissions, and we’re already about halfway through that, having emitted about 300 Gton to date. Archer points out that our remaining allowance of 300 Gton “is comparable to the remaining reserves of oil and gas”, and concludes that, “ultimately, the future of Earth’s climate comes down to decisions about coal.” That last part is hardly a shocking revelation for anyone who follows energy and environmental issues closely, but it’s good to see that there’s much more to it than merely a seat-of-the-pants, “common sense” conclusion.
The next graf, at the bottom of page 162, points out how we’re blatantly cooking the books. Incredibly, by looking at what we do and the consequences of our actions only up to the year 2100, we’re arbitrarily granting ourselves an additional 40% buffer in the amount of CO2 we can emit. As Archer puts it, “Forty percent more CO2 could be emitted by the year 2100, because in the year 2100, forty percent of the warming from that CO2 would not have happened yet. Global temperature could approach 2°C higher in the year 2100, but it could rise to maybe 3.3°C in the centuries thereafter.” Ponder that for a few moments and try to remember when anyone else besides Archer has mentioned this nasty little detail to the public.
At the bottom of page 163, Archer says that if you divide the world’s allowed CO2 emissions budget on an equal, per capita basis, you find that the developed world must make cuts of around 80%, and the US, Canada, and Australia would have to cut on the order of 90%.
On page 164 he talks about the IPCC’s stabilization scenarios, in particular, the 450 ppm scenario, which results in an 80% by 2050 guideline.
My observations on all of this:
- The 40% “bonus” we’ve awarded ourselves by limiting our analysis to the year 2100 is by far the biggest single shocker.
- The 450 ppm stabilization scenario seems to be setting an easier target than what the science argues for, namely 420 ppm. At about 7.7 Gton CO2 equaling 1 ppm of CO2 in the atmosphere, that difference of 30 ppm, assuming roughly half is absorbed by plants and the oceans in the relevant time frame, translates to about 460 Gton CO2 ((30 * 7.7)/0.5), or just over 15 years of worldwide emissions at current rates. Given the difficulties we’re likely to face in making worldwide, deep emissions reductions, that extra burden dictated by science (“what we have”), not politics (“what we want”), is bad news. (And need I point out the staggering difficulty of getting the atmospheric level of CO2 down to 350 ppm (35 ppm below current levels), the level James Hansen and others say is really necessary?)
- Even this treatment of the 40% bonus doesn’t relay its full meaning. Archer says that our lifetime carbon (in the form of CO2) emission allowance is raised from 600 Gton to 1,000 Gton. But if we’ve already emitted 300 Gton of it, then that means we’re allowing ourselves more than double the amount of emissions still available to us, 700 Gton (1000 – 300) vs. 300 Gton (600 – 300).
- One detail often overlooked is what happens after 2050. Archer includes a graph on page 165 that shows us getting to an emissions reduction of 80% by 2050, but then emissions taper off to zero by 2100. This post-2050 portion happens at a noticeably slower rate than what’s depicted in the 2000 to 2050 time frame, but we’re still not in the clear by mid-century. I suspect that even a lot of dedicated environmentalists have not only the year 2100 myopia, but also an implicit assumption that once we get down the required level in 2050 we can stay at that level of emissions “permanently”.
- The whole issue of what the starting point is for CO2 emissions reductions–1990 or some time later–is really inconsequential, in light of the above issues and how long CO2 hangs around in the atmosphere, i.e. centuries.[2]
- Notice that this discussion is entirely in terms of CO2 emissions. The current IPCC report, on page 204 of chapter 2 of The Physical Science Basis [PDF], the radiative forcing of methane already in the atmosphere is about 0.48 W/square meter, about 29% of that of present atmospheric CO2 (1.66 W/sq. meter), so it’s a non-trivial contribution. And with methane rising again after being relatively flat for a few years, even without (we hope) the permafrost bomb starting to go off, the potential role for methane becomes more interesting yet.
In short, I think we’re making this way too complicated, by focusing on an “area under the curve” calculation, meaning we’re looking at both the amount we can still “safely” emit and various schedules for lower emissions reductions subject to that overall limit. Scientists and especially policymakers need to look at this level of complexity, but mainstream consumers don’t. They need a simple measurement that’s intuitively appealing because they deal with very similar concepts in their daily lives. They need a CO2 Clock.
The CO2 Clock is simply a running count of the amount of CO2 we can still emit before hitting the limit that’s dictated by the best available science.
This is directly analogous to consumers wondering if they have enough gasoline in their vehicle’s tank to complete a trip, or if their dwindling bank account will cover next month’s expenses, or any of the dozens of other experiences we all have with a visibly depleting resource.
Of course, these aren’t a perfect analogies, and the biggest single flaw is that CO2 emissions don’t exhibit binary behavior regarding the limit. Seconds before you run out of gasoline, your vehicle runs just as well as if it had a full tank, and one second after the tank runs dry the engine stops completely. The same pattern is seen with money in your checking account, beer at a party, etc. There is no gradual shift from one state to another, but an instant state change. We’re already seeing widespread and numerous changes in the world’s climate triggered by CO2 emissions, well before we hit the 2°C “limit”. But I think this approach works well enough to overcome that break with common experience.
So, where do we stand with the CO2 Clock?
Check the Carbon Dioxide Information Analysis Center web site, and you can find their file of historical, worldwide carbon emissions, which conveniently provides numbers from 1751 to 2006, inclusive. Summing the numbers (which include cement manufacturing and gas flaring, in addition to more typical consumption of coal, oil, and natural gas) gives us 329 billion metric tons of carbon. Converting this and our 600 G ton limit Archer mentions from carbon to CO2, and adding 30 billion tons of CO2 emissions for 2007 and 2008 each and another 17 for 2009 to date, means we’ve already used up 1,281 billion metric tons of our 2,196 billion metric tons CO2 allowance.
Therefore, we have 915 billion metric tons remaining, and we’re using it up at a rate of roughly 30 billion metric tons a year. If it took you five minutes to read this post, the world emitted another 285,000 metric tons of CO2 by the time you reached this sentence, and we’ll have to deal with that CO2 for generations.
I will be adding a CO2 Countdown Clock to my EE Clocks project soon.
[1] I’m very skeptical about 2°C being “the” number, if only because of the impacts we’ll see from the continued disappearance of glaciers, which supply fresh water to a billion human beings for drinking, agriculture, hydroelectric generation, etc. As those flows start to taper off and other climate chaos effects are felt, it will put enormous stress on local populations, and very likely lead to massive numbers of climate refugees. See the new report from Oxfam Australia, for example. You can add your own estimate of what happens if less than 2°C is enough to trigger the permafrost bomb and start releasing even a tiny portion of its 1.6 trillion tons of carbon. Make your own assumption about what a “tiny portion” is (0.5%/year?), and then plug those numbers into the scenarios below. It isn’t pretty.
[2] Archer has said, “The lifetime of fossil fuel CO2 in the atmosphere is a few centuries, plus 25 percent that lasts essentially forever.” Quoted in Carbon is Forever, and supposedly in The Long Thaw, but no page number is given and I didn’t search for it.
