Revkin has leading system dynamics expert Sterman on NOAA’s 1,000-years-of-hell paper

I am a big fan of MIT’s John Sterman, one of the world’s leading experts on systems thinkers.

In a post on “The Greenhouse Effect and the Bathtub Effect,” Revkin notes that Sterman’s work trying to reduce the biggest source of climate confusion is related to the new NOAA-led paper that I discussed here: Climate change “largely irreversible for 1000 years,” with permanent Dust Bowls in Southwest and around the globe.

The bathtub analogy is that while atmospheric concentrations (the total stock of CO2 already in the air) might be thought of as the water level in the bathtub, emissions (the yearly new flow into the air) are the rate of water flowing into a bathtub. We need to lower the level, not just the flow. A great video clarifying the issue is here. It is narrated by my friend Andrew Jones. If you want to play the simulation itself, go here.

Revkin got Sterman’s comments on the paper, which I am reposting below:

I have read the Solomon paper.

It’s an excellent demonstration of the bathtub principle — the concept of stocks and flows, which prior research shows many people, even many highly educated people, don’t understand. Our mental models suggest that if we stop the growth of emissions, we will stop global warming, and if we cut emissions, we’ll quickly return to a cooler climate. We tend to think that the output of a process should be correlated with — look like — its input. If greenhouse gas emissions are growing, we think, the climate will warm, and if we cut emissions, we imagine that the climate will cool. In systems with significant accumulations, however, such correlational reasoning does not hold. Rather, it’s more like filling a bathtub. The amount of carbon dioxide in the atmosphere is like the level of water in a bathtub. The level grows as long as you pour more water in through the faucet than drains out. Right now, we pour about twice as much CO2 into the atmospheric tub than is removed on net by natural processes.

Stabilizing atmospheric concentrations requires emissions to fall to the net removal rate. Further, because of the processes highlighted in the Solomon paper and other analyses, including the IPCC AR4, the net removal of CO2 from the atmosphere is likely to fall as the stocks that absorb all that carbon, particularly the oceans, fill up. There are other key “bathtubs” — accumulations — that contribute to the irreversibility of climate change Solomon highlights. First, global mean surface temperature depends on the quantity of heat stored at the surface of the earth (earth, lower atmosphere, and the mixed layer of the oceans). That stock of heat is increased by net radiative forcing, the difference between the flow of energy coming in (primarily from the sun) less the flow of energy radiated back to space and the flow of heat transfered to the deep ocean. Today that inflow exceeds the outflow, so the average temperature is rising. Stabilizing the concentration of greenhouse gases in the atmosphere may stop the growth in net radiative forcing, but will not reduce the net inflow of energy (net radiative forcing) to zero. So temperatures will continue to rise until the planet warms enough to restore radiative balance. Solomon’s paper points out that the heat currently absorbed by the oceans does not disappear, but eventually returns to warm the surface. Thus temperatures won’t fall quickly even if atmospheric GHGs peak and eventually drop. And so on. Land-based ice in glaciers and ice-sheets will keep contributing to sea level rise as long as melting exceeds snowfall accumulation; stopping the growth of temperature would not stop the net melting.

What all this means is that the rate at which the climate returns to “normal” — say, early 20th century conditions — is so slow that, for key factors like sea level, precipitation patterns, ice sheets, and so on, the flow out of the bathtub is very very slow. So climate is a bit like the national debt. The US federal deficit has exploded in recent years, and the national debt has exploded as well. But suppose we could instantly cut the deficit to zero — drop it from about a trillion dollars per year to zero. What would happen to the debt? Of course it would not fall, but would instead stop growing at its all time peak value. Because the drains out of the various bathtubs involved in the climate — atmospheric concentrations, the heat balance of the surface and oceans, ice sheet accumulations, and thermal expansion of the oceans — are small and slow, the emissions we generate in the next few decades will lead to changes that, on any time scale we can contemplate, are irreversible.

One more critical point: it’s important that people not react to Solomon’s work with despair. Yes, a certain amount of climate change, due to past emissions, is inevitable, and will not be reversible. But it would be tragic if people concluded that therefore there is nothing we can do, that it is futile to reduce emissions, and that therefore all efforts should shift to adaptation. To the contrary: if nothing is done to cut emissions, and soon, the climate our children and grandchildren will face will almost certainly be far less hospitable, and there will be no turning back. By the time we know for certain how bad it will be it will be too late to take any corrective action. The Solomon paper should finally bury the idea that we can wait and see. It further strengthens the case for immediate, strong mitigation. The good news is that it’s getting cheaper every day to cut carbon emissions. Through learning, scale economies, R&D, and other forms of innovation, new technologies for carbon-neutral renewable energy are becoming more available and less expensive. Each megawatt of solar or wind capacity we build lowers the cost of the next and the next — a positive feedback we need to strengthen if we are too avoid irreversible harm to the ability of the planet to sustain us.


John Sterman

Jay W. Forrester Professor of Management
Director, MIT System Dynamics Group
MIT Sloan School of Management


15 Responses to Revkin has leading system dynamics expert Sterman on NOAA’s 1,000-years-of-hell paper

  1. danl says:

    Excellent letter, Joe. Thanks for posting. I’m no climate expert, but I’ve never seen GHG levels and warming explained so succinctly.

  2. col says:

    Taking this study and showing what it really means for positive action — that is, it means there’s no room for wait and see cuz we see more than enough already — is the kind of analysis and (counter-) messaging we desperately need more of. Thanks Joe. My only friendly suggestion would be to reflect that more in your title.

    [JR: Point taken. Whipped that one out. Still, The study didn’t make the front page of the New York Times or Washington Post, so I’m doing what I can to publicize it.]

  3. Vernon says:

    Since all studies to this point indicate that CO2 only has a half life of 5-15 years depending on the study, how is it that we are going to have it around for the next 1000 years?

    Since the SST has turned cold with the shift in the PDO both the fear that the seas would loose the ability to sequester CO2 is pretty much been proven false and we don’t have to worry about sea warming can creating dead zones. Go look at the Argo buoys record for deep water. There is no warming taking place.

    So with almost all studies not done by the pro-AGW crowd both before and after the AGW scare started shows that CO2 does not have a long life span.

  4. David Lewis says:

    Re: Vernon’s “point”, if one could call it that. All calculations not done by the pro 2+2=4 crowd do in fact show results other than 2+2=4, but I’m not sure what is proved by that fact.

    Moving right along. Hansen has been saying that some of the accumulated CO2 can be expected to be removeable, especially if civilization were to appreciate its peril and start to act. When he first realized that anything more than 325 – 350 ppm CO2 was “a recipe for global disaster”, he had to start thinking along those lines.

  5. Vernon,

    You seem to like Trolling here but your contributions would be better appreciated by McIntyre at Climate Audit.

    You are fundamentally mistaken that “all studies to this point indicate that CO2 only has a half life of 5-15 years”.

    Emissions of CO2 into the atmosphere do not decay like nuclear waste and the concept of “half life” is inapplicable. You need to understand the carbon cycle to understand how CO2 emissions from burning fossil fuels will continue to affect the atmosphere for thousands of years.

    Archer and Brovkin (2008) reviewed long-term carbon cycle models from the recently published literature. They noted, “carbon cycle models respond to a release of new CO2 into the atmosphere in a series of several well-defined stages lasting for many millennia.” In the first stage, fossil fuel CO2 released into the atmosphere equilibrates with the ocean, which takes centuries or a millennium due to the slow overturning circulation of the ocean.

    Archer and Brovkin (2008: 284) noted that the lifetime of individual CO2 molecules released into the atmosphere may only be a few years because of the copious exchange of carbon with the ocean and the land surface. However, the CO2 concentration in the air remains higher than it would have been, because of the larger inventory of CO2 in the atmosphere/ocean/land carbon cycle.

    That is, the equilibrium processes removing fossil fuel CO2 emissions from the atmosphere operate at a system-wide level and individual CO2 molecules do not last for millennia in the atmosphere. Thus today’s fossil fuel CO2 emissions will not be “in” the atmosphere (literally) for a long period but they will continue to “affect” the atmosphere, the climate, and the oceans for many thousands of years.

    The “bathtub principle” discussed in this post reflects a system-wide increase in active carbon levels in the carbon cycle and the slow removal of it back to storage as fossil carbon.


    Archer D and Brovkin V (2008), “The millennial atmospheric lifetime of anthropogenic CO2” Climatic Change 90:283-297 DOI 10.1007/s10584-008-9413-1, available at

  6. tidal says:

    Vern said: “Since all studies to this point indicate that CO2 only has a half life of 5-15 years depending on the study, how is it that we are going to have it around for the next 1000 years?… “

    You are misrepresenting of the science on this point. Because it’s particularly germane to both the Solomon paper and the Sternman comments, I thought I would link to Carbon is forever from Nature Reports last November, which summarizes the current literature. (The upcoming paper – “Atmospheric Lifetime of Fossil-Fuel Carbon Dioxide” – is here.)

  7. These findings reinforce a conclusion drawn from Hansen’s target CO2 work mentioned above that we need a huge agenda focused on understanding how we manage farm, grazing and forest land for maximum carbon accumulations in soil and vegetation, and then implementing those practices on a mass scale with the incentive and policy structure needed to make them happen.

    And then it gets to weird stuff like Wally Broecker’s proposed CO2 sucking technology. David Keith at UCalgary has already prototyped. Only costs about $1,000/tonne to remove and then you better make sure the energy you’re using doesn’t come from carbon sources, or push energy demand onto carbon sources.

    And it causes concern that this will be fuel for the arguments of geoengineering advocates. The moral hazard and unintended consequences problems are obvious. But we are seeing increasing momentum building in this direction.

  8. Patrick, I think this paper puts a pretty compelling case that geoengineering may well be preferable to the alternative.

    Given that, it may be best to change tack – to concentrate on opposing schemes that do anything other than CO2 removal from the atmosphere, rather than a blanket “geoengineering is bad”.

  9. Joe says:

    Respectfully, geo-engineering doesn’t exist except as a pipe dream. Should we do research. Sure. But as I wrote in the original post, let’s not be deluded into thinking that pursuing research is the same thing as having any reason to believe that research will lead to anything practical or affordable — or any more successful than the billions we have flushed down the toilet trying to build a practical and affordable hydrogen car

  10. Vernon says:

    Well, going back to pre global warming days and

    Moore, B., III, and B. H. Braswell (1994), The Lifetime of Excess Atmospheric Carbon Dioxide, Global Biogeochem. Cycles, 8(1), 23–38.

    ‘If one assumes a terrestrial biosphere with a fertilization flux, then our best estimate is that the single half-life for excess CO2 lies within the range of 19 to 49 years, with a reasonable average being 31 years.’

    But on a different topic did you notice that she found that sea level rise would only be 1 meter for 1000 years? That is a far cry from the 5 claims.

    [JR: It is most certainly NOT what she found. You should read her paper. She found a lower limit JUST due to thermal expansion of 1 to 2 meters. It is ice sheets instability, at which she did not look at, that gets you the much higher sea level rises in the recent literature.]

  11. Dano says:

    Note how “Vernon” needs to quote a 15-year old paper to make his “point”.

    That’s all denialists have: nothing.



  12. David Lewis says:

    It has been widely reported in Canada that Professor David Keith of the University of Calgary has a pilot carbon capture plant the doesn’t cost anything like the $1000 per tonne mentioned above. A news report with a photo of the pilot plant:

    “Keith and his team showed they could capture CO2 directly from the air with less than 100 kilowatt-hours of electricity per tonne of carbon dioxide. Their custom-built tower was able to capture the equivalent of about 20 tonnes per year of CO2 on a single square metre of scrubbing material – the average amount of emissions that one person produces each year in the North American-wide economy.

    “This means that if you used electricity from a coal-fired power plant, for every unit of electricity you used to operate the capture machine, you’d be capturing 10 times as much CO2 as the power plant emitted making that much electricity,” Keith says.”

  13. David B. Benson says:

    Vernon — First read David Archr’s “the Long Thaw”.

    Post comments afterwards.

    David Lewis — Thermodynamics shows this cannot work unless you then throw away (sequestr) the scrubbing material. I have forgotten just what material David Keith is using, but it seems to expensive to simply throw away.

    Another idea nailed by the hard, hard Second Law of Thermodynamics.

  14. Martin says:

    An even better point concerning Vernon: The ONE paper he cites to support his view actually contradicts it. Unless his 5-15 is somehow equal to the paper’s 19-41. And then he claims that 1994 is “pre global warming”. He is an ignorant obfuscater, pure and simple.


  15. Dano says:

    Oooh – good catch Martin.

    Let me revise my statement above:

    Note how “Vernon” needs to misquote a 15-year old paper to make his “point”.