A new estimate of carbon release from Arctic permafrost surfaced late last week. I intend to write about it, but that also requires me to quote extensively from this post, which I published on December 1, 2011. So I've reprinted it today, with only a few small edits to bring it up to date. It's a bit technical, sorry about that — Dave
I hope you've got your thinking cap on today. Although this post appears to be about climate change, it is not. I am going to use a recent news report about carbon emissions from thawing permafrost as a jumping off point in a discussion of a much broader subject—how to think about the future. This too-brief presentation is a bit complicated, so I hope you will be able to follow the discussion.
A recent study called High risk of permafrost thaw appeared in the December 1 issue of the science journal Nature. As you're probably aware, the Arctic is warming much faster than the rest of the planet, and one of the effects of that warming is to cause the permafrost to melt and break-up, thus releasing the large amounts of carbon dioxide (CO2) and methane (CH4) stored there. If you are awake, you also know that both are greenhouse gases. We are interested in this text from the study.
Our survey asks what percentage of the surface permafrost is likely to thaw, how much carbon will be released, and how much of that carbon will be CH4, for three time periods and under four warming scenarios that will be part of the Intergovernmental Panel on Climate Change Fifth Assessment Report.
The lowest warming scenario projects 1.5 °C Arctic warming over the 1985–2004 average by the year 2040, ramping up to 2 °C by 2100; the highest warming scenario considers 2.5 °C by 2040, and 7.5 °C by 2100. In all cases, we posited that the temperature would remain steady from 2100 to 2300 so that we could assess opinions about the time lag in the response of permafrost carbon to temperature change.
The survey was filled out this year by 41 international scientists, listed as authors here, who publish on various aspects of permafrost. The results are striking. Collectively, we hypothesize that the high warming scenario will degrade 9–15% of the top 3 metres of permafrost by 2040, increasing to 47–61% by 2100 and 67–79% by 2300 (these ranges are the 95% confidence intervals around the group’s mean estimate). The estimated carbon release from this degradation is 30 billion to 63 billion tonnes of carbon by 2040, reaching 232 billion to 380 billion tonnes by 2100 and 549 billion to 865 billion tonnes by 2300. These values, expressed in CO2 equivalents, combine the effect of carbon released as both CO2 and as CH4.
This sounds pretty terrifying, and it is scary when viewed over long periods (centuries) on the human timescale. (On the geological timescale, a few centuries amounts to no time at all.) These scientists are talking about the years 2040, 2100, and 2300! Let's disregard the far-flung future and focus on the predicted carbon release by 2040.
Any such survey of expert views is only as good as the assumptions underlying those views. Notice that estimates of greenhouse gas release from thawing permafrost are based on the four warming scenarios which will be part of the IPCC's Fifth Assessment Report (AR5). These scenarios are unnamed in the Nature article, but a little digging helped me identify them. (Google is your friend.) Here they are.
Click on the image to enlarge it. On the left, radiative forcing (heating of the Earth's surface) in watts/m2. On the right, anthropogenic emissions scenarios. It is highly likely that the four scenarios used in the Nature study were MESSAGE 8.5, AIM 6.0, MiniCAM 4.5 and IMAGE 2.6. Here's my source, which is corroborated here.
If you look closely at the right panel, you will see the four emissons pathways corresponding to the scenarios. Let's throw out the high case (MESSAGE 8.5) and the low case (IMAGE 2.6). In the former, anthropogenic emissions just rise and rise, eventually reaching 100 billion tons (gigatons, gt) per year. In the latter, which may appeal to some Doomers in the audience, emissions rise only a little from their current level of 33 gigatons per year and fall off sharply after 2020. No doubt the people who created this scenario were not considering a possible collapse of industrial civilization. They were thinking instead that humankind made a concerted effort to reduce emissions, which appears to be more and more unlikely.
As we consider the middle scenarios AIM 6.0 and MiniCAM 4.5, we must bear in mind this very important point:
All other things being equal, anthropogenic CO2 emissions are a proxy for economic growth*
* "a proxy for" in this context means "provide an alternative measurement of", or "stand in for"
As things stand, and in the foreseeable future, anthropogenic emissions from burning fossil fuels will rise if and only if the global economy is growing. See my recent post For Humans, The Economy Is Everything. Also see my much longer essay Economic Growth And Climate Change — No Way Out? (This long essay is not for the faint-hearted.)
OK, let's return to the two middle scenarios. In MiniCAM 4.5, annual emissions grow slowly from the current level to about 38-39 gigatons in 2050, which is a mere 39 years from now. In the AIM 6.0 scenario, annual emissions grow to about 53-54 gigatons in 2050. We are thus entitled to conclude that both scenarios assume the global economy will continue to grow for the next 39 years. Let's split the difference between the two. Let's create a scenario called DAVE 1.0 in which emissions grow to about 45-46 gigatons per year by 2050. Let's take that as the default scenario assumed by the IPCC and the authors of the Nature study.
Getting back to thawing permafrost, the survey results published in Nature assume that emissions from the frozen tundra will be anywhere from 30 gigatons of CO2-equivalent (the low-end IMAGE 2.6 scenario) to 63 gigatons (the high end MESSAGE 8.5 scenario). Let's split the difference again, and assume that emissions will be about 45-46 gigatons from thawing permafrost by 2040 according to the DAVE 1.0 scenario. (I am simplifying here by assuming a linear relationship, but that really doesn't matter much.)
And now we are finally ready to ask the crucial questions all of this discussion has led up to.
- How likely is it that we will follow an economic growth path where the cumulative total emissions from thawing permafrost are about 45-46 gigatons by 2040? And annual anthropogenic emissions are 45-46 gigatons by 2050?
- Relatively speaking, how important is it that all emissions from thawing permafrost will total 45-46 gigatons by 2040, which is about 140% of total anthropogenic emissions in 2010? (Of course, emissions from permafrost will grow for a long time after 2040.)
In short, do you find it plausible that the global economy will grow and grow for the next 39 years? If you think this likely, or even possible, you should worry about CO2 emissions from thawing permafrost. If you don't find DAVE 1.0 plausible, and regular DOTE readers know I don't, you're likely to shrug off this Nature survey about future emissions from thawing permafrost, reasoning that there are plenty of other things to worry about; this is only one of them.
For example, what will global oil production be in 2040? What will it be in 2050? In my view, it's not only likely, it's almost a certainty that global oil production will be considerably lower in three or four decades than it is right now. Perhaps you think that makes no difference to future economic growth. I beg to differ.
Now you can see, perhaps with new eyes, that scary scenarios about emissions from thawing permafrost (and the like) are predicated on what I call Dumb Extrapolation of 20th century economic growth trends well into the 21st century. We also see this in Congressional Budget Office (CBO) reports on future deficits. Future deficits are estimated to be far smaller than they likely to be based on highly unrealistic future economic growth rates which, all other things being equal, boost government revenues. When officials representing large human institutions like the IPCC or the CBO talk about the future, you will invariably find Dumb Extrapolation.
I hope you've followed this complex argument and have learned something about how to think about the future. By definition, Dumb Extrapolation excludes the possibility of radical discontinuities in all areas of study—the climate, the oil supply, the coal supply, the world economy, the American economy, CO2 emissions from thawing permafrost, future government revenues and so on.
Truth be told, I have been forced to use a form of dumb extrapolation today with respect to future permafrost emissions to make a larger point.
One such "radical discontinuity" (i.e. a non-linear event in the economy) occurred in 2008. It is three four years later, and we in the United States are all still paying the price. Europe is (still) teetering on the edge of economic castastrophe. China appears to be is in big trouble, given their failing export model and bursting real estate (housing) bubble. Thinking about what the world will look like in 2040 is sufficiently mind-boggling, let alone thinking about what might happen by 2100 or 2300.
This choice quotation from the great Yankee catcher and sage Yogi Berra seems apropos here.
The future ain't what it used to be
Bonus video — Peter Gabriel's end theme Down To Earth, from the movie Wall-E