Dyson Exegesis

Freeman Dyson starts an article with the words “My first heresy says that all the fuss about global warming is grossly exaggerated. Here I am opposing the holy brotherhood of climate model experts and the crowd of deluded citizens who believe the numbers predicted by the computer models”. Yet his article is hardly about climate models, or their relationship to experts or citizens, at all.

I personally have no disagreement with the “third heresy”, the idea that the USA is at the end of its hegemony, by the way. I actually think this is occurring now, not 50 years hence as Dyson suggests. I have no idea what this has to do with the purported intent of Dyson’s essay, though.

The primary practical (as opposed to theoretical) problem our field needs address these days is to identify specific regional trends and risks, to inform adaptation. This is as opposed to the mitigation question, whether and how much to change our behavior to reduce climate impacts.

The question of how much to mitigate or not is not primarily about climate science anymore, but about economics, ecology, and values. Dyson points out that this is not “a problem in meteorology”, and on this point, it must be said, he is very much correct. We already know that the global temperature sensitivity to equivalent CO2 doubling is near 3 degrees C.

The fact that this is considered to be in doubt is a consequence of people using meteorological uncertainty as a diversion, in order to avoid the issue for as long as possible. Dyson fails to understand how this is happening. Like most older scientists he lives in an older, more civilized world than the rest of us occupy. So he misunderstands where the controversy comes from.

That said, his position seems to meander: carbon is a land management problem, but it isn’t a problem anyway, and we might kick off an ice age and we might not and… Many of the common misconceptions and not uncommon hubris are scrambled together here. This isn’t a serious article, it’s an intelligent but essentially uninformed rant. Unfortunately I have to call it irresponsible.

It’s also a bit incoherent. So I respond below to some of the individual points made without further summary.

Dyson’s text is in blue, my responses in black. Hopefully people inclined to take Dyson seriously on this matter will come by here and think again.

PART I Paragraph 2

The models solve the equations of fluid dynamics, and they do a very good job of describing the fluid motions of the atmosphere and the oceans. They do a very poor job of describing the clouds, the dust, the chemistry and the biology of fields and farms and forests. They do not begin to describe the real world that we live in. The real world is muddy and messy and full of things that we do not yet understand. It is much easier for a scientist to sit in an air-conditioned building and run computer models, than to put on winter clothes and measure what is really happening outside in the swamps and the clouds.


That is why the climate model experts end up believing their own models.

Um, I must have missed a step here… In fact climate model experts do not particularly “believe” models. Our skepticism is informed and consequently rather complex. Do we believe this, did we capture that… So here Dyson is completely off base.

Paragraph 3

the warming is not global

This is just confusion. He should read my realclimate article on the definition of “global warming”.

Paragraph 4

The number that I ask you to remember is the increase in thickness, averaged over one half of the land area of the planet, of the biomass that would result if all the carbon that we are emitting by burning fossil fuels were absorbed. The average increase in thickness is one hundredth of an inch per year.

Per YEAR!!! On every piece of viable land, under economic use or otherwise… He certainly identifies a viable carbon sequestration sink, but the idea of an inch of graphite per century being redistributed on all land everywhere in soil restructuring is hardly a trivial matter to handwave away.

Anyway, notice he is already wandering away from climate modeling and has said very little about it.

Paragraph 5

Changes in farming practices such as no-till farming, avoiding the use of the plow, cause biomass to grow at least as fast as this. If we plant crops without plowing the soil, more of the biomass goes into roots which stay in the soil, and less returns to the atmosphere. If we use genetic engineering to put more biomass into roots, we can probably achieve much more rapid growth of topsoil. I conclude from this calculation that the problem of carbon dioxide in the atmosphere is a problem of land management, not a problem of meteorology.

Well, it certainly isn’t an EASY problem in land management. However, I agree with Dyson that the focus on meteorology is misplaced in the mitigation arguments. Climate science is crucial on the adaptation side, but all the focus on it on the mitigation side is a red herring and a vicious one.

What Dyson is proposing here seems at first blush unrealistic to me. Of course I’m always hopeful when a mitigation startegy is proposed that doesn’t involve too much disruption. I don’t know if he’s talked to soil experts or agronomists. What it is, is a very coarse approach to a mitigation strategy.

Let’s be pleased, at least, that Dyson acknowledges a problem of carbon dioxide in the atmosphere.

Paragraph 7

When I listen to the public debates about climate change, I am impressed by the enormous gaps in our knowledge, the sparseness of our observations and the superficiality of our theories. Many of the basic processes of planetary ecology are poorly understood. They must be better understood before we can reach an accurate diagnosis of the present condition of our planet.

Well, the topic has suddenly lurched to ecology. This has little to do with climatology. I think I can say that ecologists I know would tend to agree with this, but it has nothing to do with what is normally charitably described as “anthropogenic global warming skepticism”. That’s not the disturbing part, though. This is:

When we are trying to take care of a planet, just as when we are taking care of a human patient, diseases must be diagnosed before they can be cured.

Yikes! So should the patient keep ingesting the toxin meanwhile?

PART III Paragraph 3

If human activities were not disturbing the climate, a new ice-age might already have begun.

Maybe so.

We do not know how to answer the most important question: do our human activities in general, and our burning of fossil fuels in particular, make the onset of the next ice-age more likely or less likely?

Nonsense. (He wheels out the usual misinterpretation of Broecker’s ocean-driven change scenario, but no scientist is expecting any ocean circulation changes to overwhelm the huge warming and kick off an ice age.) This is simply a layman’s mistake and totally out of line with the evidence. Here he is simply substantively wrong, and repeating a common misconception.

PART IV Paragraph 2

First, if the increase of carbon dioxide in the atmosphere is allowed to continue, shall we arrive at a climate similar to the climate of six thousand years ago when the Sahara was wet? Second, if we could choose between the climate of today with a dry Sahara and the climate of six thousand years ago with a wet Sahara, should we prefer the climate of today? My second heresy answers yes to the first question and no to the second. It says that the warm climate of six thousand years ago with the wet Sahara is to be preferred, and that increasing carbon dioxide in the atmosphere may help to bring it back. I am not saying that this heresy is true. I am only saying that it will not do us any harm to think about it.

It does no harm to think about it, but it can do a great deal of harm for a celebrated person to speculate in an uninformed and incorrect way. We are changing the overall forcing of the system much more than the shift from 6000 years ago to today. The extent to which this is the case is quantifiable.

Essentially the natural shifts on that time scale amount to moving solar input from one season to another. The climate system responds in interesting ways, ways which, by the way, are replicated by climate models operating from first principles.

Our present forcing operates at all latitudes in the same direction. The system cannot respond identically. Humans are focussed on climate at the surface, but physics cares about the entire depth of the atmosphere; surface conditions are an important but not a dominant component. We cannot replicate a prior natural climate with an atmosphere whose radiatively active components are different than those seen in nature.

The idea that we will drift smoothly into and settle down to a lusher more convenient climate is a fantasy and a rather stupid one. Yes, a blundering near unconscious drunk could, in fact, blunder into a wonderful jet-setters party and be celebrated for his wit and plied with champagne and caviar. This is no reason for him not to sit down and recover his wits; the champagne thing is rather a long shot.

Update: Promoted from comments:

Ugo Bardi said…

Excuse me. I have a question. At some point Dyson says:

In humid air, the effect of carbon dioxide on radiation transport is unimportant because the transport of thermal radiation is already blocked by the much larger greenhouse effect of water vapor. The effect of carbon dioxide is important where the air is dry, and air is usually dry only where it is cold. Hot desert air may feel dry but often contains a lot of water vapor. The warming effect of carbon dioxide is strongest where air is cold and dry, mainly in the arctic rather than in the tropics, mainly in mountainous regions rather than in lowlands, mainly in winter rather than in summer, and mainly at night rather than in daytime. The warming is real, but it is mostly making cold places warmer rather than making hot places hotter. To represent this local warming by a global average is misleading.

I am not sure of whether this is correct or not. Sounds reasonable, but, on the other hand, considering the level of the rest, it may not be. Is this the reason why the higher latitudes are warming more than the lower ones?

My reply:

Thanks Ugo. I’m really astonished that I missed this. I must have been rolling my eyes up a little too high.

The argument you quote is invalid for two reasons.

First, the greenhouse effect never fully saturates; increased optical depth continues to warm the surface long after the atmosphere is essentially opaque to outgoing infrared waves.

Second, for the most part there is little overlap between the absorption bands of H2O and CO2.

The idea that the effect applies “mainly in mountainous regions rather than in lowlands” is particularly astonishing. It is exactly 180 degrees from the truth.

It is the integrated column depth of greenhouse gases that trap the outgoing IR. Mountains, being nearer the top of the atmosphere, experience less greenhouse warming than the surface.

So “particularly in the mountains” shows that the author has never even sat down with the undergraduate level approximation of how atmospheric radiative transfer actually works. It’s really quite shocking.

In fact, the high latitudes are more sensitive to warming. However this is not because they are dry but rather, in part, because of the persistent presence of low clouds, (exactly contrary to the tale he is trying to spin) as well as ice-albedo feedback. See, e.g., Holland and Botz

Update 3/29/09: See also: Slicin’ and Dicin’ with Dyson and Bryson in response to recent coverage of Dyson with reference to an interesting precedent.

Update 1/23/10: See also: Guest Posting: Expanded Dyson Exegesis .