Sunday, January 28, 2007

The fox, the hedgehog and the spherical elephant...

Roger Pielke Sr. has a thing for land use. He believes that it is a much more important forcing than greenhouse gases. Frankly, he also believes that anything else is a much more important forcing, but, dear readers, that need not concern us here. Eli constantly interjects that pushing land use to the fore requires one to ignore a number of facts among which are that land use CHANGES contribute both positive and negative forcings. To first order it is the sum the International Panel on Coney Cuteness is seeking, plus which there isn't that much land to start with, and the amount is decreasing as sea levels rise. There are many ways that land use can affect climate, and it certainly is a huge driver of local climate, but greenhouse gases increases drive the global climate uniformly in one direction.

This difference reappears continually, both in science and art. Physicists are hedgehogs, everything is spherical, including elephants and there are but a few basic "truths", aka theories. Some physicists believe there is only one true theory that binds them all. For biologists, at least until recently, every one of a zillion things is different and must be sniffed. Cladisitics, the naming and description of things is basic. Eli trained as a physicist and wandered into chemistry as a young and clueless postdoc.

This dichotomy, most famously explored by Isaiah Berlin (pronounced eye-Zie-uh) and posthumously by Stephen J. Gould, is described in a great and entertaining speech/essay by John Kihlstrom

Archiolus: "The fox knows many things, but the hedgehog knows one big thing". At one level, this aphorism reflects the difference between the fox, with lots of resources at its command, and the hedgehog, with only a single, but highly effective, defense against them. But there is probably more to it than that, as Berlin made clear in his essay:
Taken figuratively, the words can be made to yield a sense in which they mark one of the deepest differences which divide writers and thinkers, and, it may be, human beings in general. For there exists a great chasm between those, on one side, who relate everything to a single central vision, one system, less or more coherent or articulate, in terms of which they understand, think and feel – a single, universal, organising principle in terms of which alone all that they are and say has significance – and, on the other side, those who pursue many ends, often unrelated and even contradictory, connected, if at all, only in some de facto way, for some psychological or physiological cause, related to no moral or aesthetic principle. These last lead lives, perform acts and entertain ideas that are centrifugal rather than centripetal; their thought is scattered or diffused, moving on many levels, seizing upon the essence of a vast variety of experiences and objects for what they are in themselves, without, consciously or unconsciously, seeking to fit them into, or exclude them from, any one unchanging, all-embracing, sometimes self-contradictory and incomplete, at times fanatical, unitary inner vision (p. 436-437.
Adopting a simile first propounded by the drunkard Christopher Hitchens in Slate, there are those like Chilingar and Khilyuk who are neither foxes nor hedgehogs but simply as dumb as stumps, but here Roger is a fox, and Eli is a hedgehog. Still, in contrast to Isaiah Berlin (pronouned eye-Zie-uh), the noble hare would consider himself a hedgehog with fox like tendencies (RTFR), a somewhat isolating predilection for a bunny.

BOE is back of the envelope, something we used to do on old Publisher's Clearinghouse mailings by the embers of the fire back in the burrow. Let us take a first cut at calculating the intensity of forcing from land use changes necessary to match that from greenhouse gas (GHG) forcing. this is going to be a very rough first cut, which will be improved with time, however, there is a benefit in putting down the rough version first and then polishing it.

We can get the GHG forcing from the IPCC TAR, 2.43 W/m^2[10% uncertainty] with 1.46 W/m^2 from CO2. The same source puts land use change forcing at -0.20 W/m^2 with the vast majority of the change in the northern hemisphere, but this is very rough, including mostly albedo changes, but not a host of other potential causes. We will return to this, or rather I expect Roger to do so here or there.

To do the calculation, we first need the total surface area of the earth. According to the physicist's spherical elephant code, as a rough estimate, one could take the radius, and use 4 pi r^2. Using a radius of 6371 km, this gives a surface area of 5.098 x108 km2 . We would then estimate 2/3 of this is ocean, leaving a land area of 1.699x108 km2 .

A biologist would name each square meter and add up all the Tom, Dicks and Rogers. But we have the Internet, and a bit of googling finds that the land area of the earth is 148.847 x 106 km2 and the sea area is 361.254x106 km2. Turns out that comes from the Chemical Rubber Company Handbook of Chemistry and Physics, something no Rabett hole should be without.

The total surface area is 5.10101 x108 km2. Since 1 km = 1000 m, a km2 has 1 x106 m2 that is 5.10101 x 1014 m2 and the total greenhouse gas forcing is Area x forcing = 1.240 x 1015 W. The surface area of the oceans is about 71% of the total surface area of the earth. Even if land use had changed over every square meter of the earth, the forcing due to land use would have to be 3.4 times that due to greenhouse gases or 8.33 W/m^2, but this is no where near the case.

True, urban areas have grown. For example in the US, urban areas went from 25,500,000 acres in 1960 to 59,587,000 in 2002. But the total land area in the US is 2,263,962,000, so even in 2002, the fraction of land in urban areas is 2.5% . Cropland changed from 341 million acres to 337 in 2005. Moreover all the changes are not in the same direction. There is lots of land in the world's deserts. While some deserts have grown, others have not, and dryland like the Sahel cycles between wet and dry. Let us be generous and assume there is a 20% change in the use of land over the past 50 years and that all of the changes associated with land use were positive. In that case, EACH m^2 of the land would have to be associated with a forcing of over 40 W/m^2. Hold your hand on a 40 W electric bulb (Mom Rabett won't use anything over 20. Here at Rabetts end we are safe, but blind).

We can improve this with improved land use data. Eli will look for it. He can find information on the US, but oom (order of magnitude. Oooom aids meditation, oooom pah pah is satisfying.), while land use is an important driver of climate, it does not look reasonable to call it the driver.

Remember, the IPCC TAR estimates TOTAL land use forcing as -0.20 W/m^2 with about the same uncertainty. Guess why.

UPDATE: The Pig wants to see the forcings:


Anonymous said...

What about the changes in permafrost etc, which are turning white reflective surfaces into nice dark absorptive ones?

EliRabett said...

That's a feedback, not a forcing.

Anonymous said...

"Some physicists believe there is only one true theory that binds them all."

You meant "blinds" right?

"One true theory that blinds them [physicists] all".

Hmm, I wonder which theory that might be.

Anonymous said...

Why guess?

Here's the answer from the IPCC TAR

"From 1850 to 1998, approximately 270 (+ 30) Gt C has been emitted as carbon dioxide (CO2) into the atmosphere from fossil fuel burning and cement production. About 136 (+ 55) Gt C has been emitted as a result of land-use change, predominantly from forest ecosystems. This has led to an increase in the atmospheric content of carbon dioxide of 176 (+ 10) Gt C. Atmospheric concentrations increased from about 285 to 366 ppm (i.e., by ~28%), and about 43% of the total emissions over this time have been retained in the atmosphere. The remainder, about 230 (+ 60) Gt C, is estimated to have been taken up in approximately equal amounts in the oceans and the terrestrial ecosystems. Thus, on balance, the terrestrial ecosystems appear to have been a comparatively small net source of carbon dioxide during this period. [1.2.1]"

CapitalistImperialistPig said...

Not a forcing either, but distinguished scientific old guy (and skeptic) Freeman Dyson thinks sequesterering just a wee bit more carbon in topsoil would change that CO2 a lot. I think he said something like an average depth of 1 cm or so. Comment?

PS - I note without other comment that you never responded to my crushing refutation of your "property = theft" assertion.

CapitalistImperialistPig said...

The IPCC numbers make it clear that the land use forcing *is* large - approximately half as large as the fossil fuel impact.

The net terrestial ecosystem impact is not much more relevant to the issue than the fact that the net of oceanic uptake and fossil fuel impact is also small.

So now don't you owe RP sr. something more contrite than a smack on the head?

EliRabett said...

IPCC shows net land use forcing as -0.20 +/- 0.20 W/cm2. That is large?

As to property being theft, show me a land title that did not originate in theft by stealth or war.


EliRabett said...

Oh yeah, carbon in the top cm of topsoil is pretty easily converted to carbon in the atmosphere, but that also falls to the you can only build topsoil in very small parts of the total surface, so a cm overall is a couple of meters where you can do it.

Further, if this were real, what would have happened to CO2 mixing ratios when the prarie (sp) was converted to farm. Sorry Freeman, no banana

James Annan said...

Pig, you seem to be counting the GHG emissions from land use as "land use forcing". While technically valid at one level, this isn't the same thing as the albedo (and sundries such as evaporation and roughness) changes that RPSr is always banging on about.

CapitalistImperialistPig said...

James and Eli,

I am not talking about albedo forcing. I am talking about the 136 Gt of Carbon injected by land use changes cited by the IPCC.

Eli - As I mentioned in response to your original p=t post, real estate titles have typically originated in occupation by humans of originally unoccupied (by humans) land.

The world, however, is old, and war and theft are as endemic to our race as property, so only a very few pieces of land have not changed hands by war or theft at least once in that long history. There are, however, pieces of land still occupied by descendants of the original settlers. To say that real-estate is theft, though, just because it has been affected by war or theft sometime in human history, makes as much sense as saying that "CO2 is life" just because of the undoubted truism that almost every carbon atom in the atmosphere has at some time in its history been incorporated in a living cell.

Anonymous said...

Ouch - undoubted truism -

I think I meant "manifest truthiness"

or maybe ...


EliRabett said...

can you point me to the direct cite. ?

EliRabett said...

Eli believes that the 136 Gt C is the TOTAL since about 1850. Since that was pretty much done by 1920 and since that correxponds to the settlement of western NA, Australia and large parts of South American and Africa by folk who stole the land, Eli believes that this is what is technically known in the pundit trade as a twofer.

Steve Bloom said...

I have never seen RP Sr. produce hard numbers to back up his assertions about forcings. It seems that for him all forcings are "first order" (has he ever listed a second order one?) and so equally deserving of consideration. Having established that, he observes that we should pay the most attention to land use forcing since in a given region it can be the dominant forcing. Finally he notes with satisfaction that the regional models have no skill. It's amazing how he is able to justify devoting so many words to painting (and repainting and repainting) himself into that logical corner.