Dyson Critique watch

The Dyson Critique (the Lucas Critique for the macro-climate) says that climate models that assume constant feedback effects with the increase of CO2 are unreliable predictors of climate change. Here’s another great discussion of the issue:

If that is not enough, changes in CO2 in the real world would almost certainly be associated with other changes in the atmosphere – sulfur dioxide, mineral aerosols (dust), ozone, black carbon, and who knows what else would vary through time and complicate the “all else held constant” picture. By the way, the Sun varies its output as well. And when discussing climate change over the next century, even more uncertainties come from estimations of economic growth, adoption of various energy alternatives, human population growth, land use changes, and … you get the message.

He goes on to say there have been recent estimates of, what economists would call, the reduced form parameter — the sensitivity of the atmosphere in terms of temperature increases to increasing CO2 levels. Basically, by looking at levels of atmospheric dust, and their correlation with CO2 levels, during previous warming periods, scientist were able to estimate the reduced form parameter. He reports that their conclusion is that climate sensitivity is lower than previous estimates which means we should expect less warming than previously estimated.

There is no discussion, however, of what economists call the structural parameters. Why is there a connection between CO2 levels and dust levels, for example? If there’s a third force that is driving both CO2 levels and dust levels, then its not clear the new estimates of sensitivity are applicable to the climate today. My understanding is that in the past, CO2 wasn’t driving climate change, climate change was driving CO2 levels and CO2 was acting as a positive feedback. The earth warmed, the ocean’s emitted their stores of CO2 causing further warming. Given the climate didn’t become unstable, I assume there were also negative feedbacks that brought the system back into equilibrium.

Its not clear though that those negative feedbacks had anything to do with CO2 levels. The pertinent question then is: can historical data tell us anything about the climate feedbacks from increasing CO2 levels today?

6 thoughts on “Dyson Critique watch”

  1. I don’t think there are “structural” relations in fluid dynamics, but I might be very wrong.

    Are you looking for some sort of chemical reaction involving CO2 and dust or something? The narrative, as it were?

    Also, thou shall not take Lucas’ name in vain. 50 Hail Barros!

  2. “their conclusion is that climate sensitivity is lower than previous estimates which means we should expect less warming than previously estimated.”

    Referencing, I assume,
    “(IPCC) suggests that the sensitivity is between 0.48 and 1.40 degrees Kelvin (K) per one Watt per square meter (Wm-2) which translates into a global warming of 2.0 K to 4.5 K for a doubling of CO2 concentration…”
    -followed by-
    “…what we have is the IPCC predicting global warming of 3.2°F to 7.2°F for a doubling of CO2 concentration. Others have shown in very credible professional journals that there is a 66% chance of the IPCC being right in their estimate…”

    Dunno why he brought Fahrenheit into it. The Fahrenheit numbers would be higher, anyway.

    CO2 can be introduced into the atmosphere by, hm, geological activity (volcanoes, vents, etc), biological respiration, chemical weathering of rock, maybe other changes in ocean chemistry that cause it to release dissolved CO2. CO2 can be removed from the atmosphere over the long run by biological processes (coal and limestone formation come to mind). Dust could be volcanic activity, meteors, and erosion. Dust doesn’t stay in the atmosphere for very long, though.

    Off-the-cuff amateur hypothesis? Event puts dust into air. Dust alters the long-term biological makeup before it settles, affecting CO2 fixation rates.

  3. Well, as preferences aren’t stable, there’s no structural relationships in economics either…

    Gotta draw the line somewhere. The critiques (Lucas’ or Dyson’s) are basically that the status quo relies (or relied) too heavily on macro correlations and not enough of deeper structure.

  4. swong, yeah you’re list of natural causes for the concentration of CO2 to rise seems right to me.

    My concern is with estimating raw correlations between CO2 and temperature controlling for these natural factors. The fact is humans are driving the increases in C02 now, so its not clear that we’re going to see dust or whatever other natural negative feedback mechanisms arise.

    Here’s a scenario (that I’m pulling from my ass, but I’ll use for illustration): let’s suppose in the past episodes of warming were caused exclusively by giant volcanic eruptions. This puts greenhouse gases in the air, which disperses over the globe quickly, and dust, which takes decades to disperse. So looking at past data, we see strong correlations between warming and CO2 and between CO2 and dust . So, being careful scientists we measure the correlation between CO2 and temperature making sure to control for the increase in dust during warming periods. Because dust tends to have a cooling effect, we see that our new estimate of the correlation between CO2 and temperature is less than when its estimated without the effects of dust.

    Using this new estimate of the correlation to understand the effects of human emitted CO2 is problematic. Why would we think in the case of human generated CO2, we’d see more dust in the atmosphere?

  5. Actually, volcanic ash can disperse pretty quickly; months, not decades.

    On the other hand, CO2 stays in the atmosphere for a long time. I think this is why it’s the poster child for greenhouse gases; its effect is the smallest, but it’s more stable than water vapor, methane, or nitrous oxides.

    Speculating on dust sources: erosion from deforestation. Desertification from diverted watersheds and poor agricultural policies (the dust bowl of the ’30s is thought to have come about through a combination of drought and bad land management).

    More speculating: take a region out of its normal temperature/precipitation range for a little while. Plants die off, topsoil is exposed, topsoil blows away.

    Unknown: How much dust do you need for it to show up in an Antarctic ice core sample?

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