Friday, December 05, 2008


In a recent Science perspective Peter Cox and Chris Jones show why things are probably worse than we think and may become worse than we can think. A major issue for climate science is the availability of a second Earth. A duplicate would be very handy to experiment on, or at least use as a second example. This, of course means that we can study in detail what is happening today, and in the absence of a way-back machine we can use proxies to look at the past. However, in both these activities, natural variability (aka a combination of random chance, chaotic behavior and stuff we don't know enough about) provides wide ranges of various climate sensitivities and looking at only one period badly constrains them.

While there are not very many if any unknown unknowns there sure are a pile of badly known knowns (Eli plays the anti-Rumsfeld here) among which are CO2 sensitivity of carbon stores and the climate sensitivity of CO2.

The first is one of the denialists' favorite outs. It expresses how increases in CO2 will increase (or decrease) the amount of carbon stored in soils/oceans, etc. It determines changes in the flux of CO2 from the atmosphere to other reservoirs and is given in GtC/ppmv or gigatons of carbon stored elsewhere per part per million change in atmospheric CO2. The ranters from the right (mostly they come from there although some are way out in left field and others, like the Larouchies are commuting from Mars) claim that plants will flourish at high atmospheric CO2 in a slightly warmer world, net primary production of vegetative matter increase and, dear Candide Bunny this will be the best of all possible worlds. Unfortunately for us, it appears that this effect will saturate well before Peabody digs up all the coal and burns it.

The second, on the other hand (this is a Science blog at base, and there is nothing without caveats) asks the question, if you have increase (or decrease the amount of carbon in soils and the oceans, how does that affect the global temperature. It is expressed in GtC/K or the change in the amount of stored carbon per degree K. Now there are several effects here. One, of course is you can change the amount of carbon stored by burning fossil fuel. Or you could change it by decomposing leaves (something we in the Northern Hemisphere are currently doing, come to think about it we are also burning a lot of fossil fuel). Or you could change it if the temperature of the oceans changes, and so on.

Cox and Jones point out that modern measurements badly constrain both of these (pink band in the leftmost part of the image from their article) given interannual variability (light green band, the overlap being shown in brown), but that if we add information from the Little Ice Age in the Northern Hemisphere (turquoise band in the rightmost panel) we can narrow the range considerably (purple area in the right panel).

First, Eli obviously has to work on him image skills, but in the meantime you can click on the image to get a clearer view. Second, the middle panel clearly shows a case where temperature driven by other forcings drives CO2 concentrations, but as has been pointed out n+1 times, CO2 in the atmosphere can both be a driving force as is the case when we burn fossil fuel, and a response or feedback, as when, for example the sun cools or heats up.

Eli, being a sunny bunny will leave the last word to Cox and Jones (emphases added for our denialist friends)

The perturbations of climate and CO2 during the LIA period from 1500 to 1750 are strongly correlated, with climate leading CO2 by ~50 years (11). These records indicate a tight relation between CO2 and climate, with a gradient of 40 ppmv/K. However, given the discrepancies between different temperature reconstructions, and the uncertainties associated with interpreting Northern Hemisphere climate proxies in terms of global mean temperature, we estimate a gradient of 20 to 60 ppmv of CO2 per kelvin of global warming (see the figure, middle panel).

This is a conservative estimate based on the assumption that human CO2 emissions from land-use change were not significant in the LIA, which seems consistent with the strong lead-lag relationship between climate and CO2 during this period. Even so, the estimate is at the high end of the 20th-century simulations with the IPCC C-CC models, encompassing only the model with the largest feedback over this period. When considered alongside contemporary constraints, the LIA data thus enable a much tighter constraint on the climate and CO2 dependences of the carbon cycle (see the figure, right panel).

The LIA data imply that atmospheric CO2 will increase more quickly with global warming than most models suggest. One implication is that the 20th-century CO2 rise due to anthropogenic emissions may have been amplified by 20 to 30 ppmv through the impacts of global warming on natural carbon sinks. Furthermore, the existence of a strong climate effect on the carbon cycle indicates that larger emissions cuts are required to stabilize CO2 concentrations at a given level. The LIA is just one example of a natural climatic anomaly in the past that can provide insights into the strength of the coupling between the Earth's climate and carbon cycle. Paleoclimatic data cannot tell us how to meet the challenge of managing 21st-century climate change, but they can help us to better understand the nature of this challenge.

Read the comments for further enlightenment


Horatio Algeranon said...

Eli said; "While there are not very many if any unknown unknowns..." [which Rumsfeld describes as "things we do not know we don't know."]

Horatio is curious: how is it possible to know how many "unknown unknowns" there are?

Marion Delgado said...

Horatio: You ask Achmed Chalabi.


Mike Tobin asks why, when virtually all the feedbacks are positive, we aren't in worse shape by now than we are?

It's an interesting question.

Horatio Algeranon said...


Horatio wishes to know "how it is possible to know how many 'unknown unknowns' there are".

But he does not wish to know it badly enough to go on a Wild Chalabi hunt with Dick Cheney.

Horatio may have a tiny mouse brain, but he ain't no fool.

Tilo Reber said...

It's also worth asking the value of using the LIA as a vehicle for constraint. It isn't necessarily typical. There have been times when the CO2 trend trailed the temperature trend by as much as 800 years.

Of course such a large trail makes one question it's value as a feedback mechanism. Furthermore, the way that temperature trends reverse directions in the face of CO2 feedback that should be reinforcing the direction prior to the reversal, makes one question it's strength as a forcing factor.

Anonymous said...

"Of course such a large trail makes one question it's value as a feedback mechanism."

Only if one is a complete idiat and has nevert paid attention to the science. Absent evidence for a huge natural CO2 source other than the oceans, the lack of a lag would violate the laws of physics. Perhaps that's why one was predicted in 1983 (before the ice cores).

Gareth said...

One would imagine Bill Ruddiman might have a thing or two to say about the land use change driving CO2 levels during the LIA...

David B. Benson said...

What Gareth wrote.

Tilo Reber said...

"Absent evidence for a huge natural CO2 source other than the oceans, the lack of a lag would violate the laws of physics."

Which laws of physics, exactly, say that it can take up to 800 years for the warming in the atmosphere to result in an increase of CO2.

I guess any air head that knows absolutely nothing about physics can claim that what is happening must me happening according to the laws of physics.

Of course there are other papers that indicate that the connection between CO2 release and deep sea temperature is not as simple as most warmers would like to believe.

EliRabett said...

Most of the large land use changes come from deforestation between 1800 and 1900 with the settling of the American/Canadian west, the pampas of Argentina and the development of Australia.

This is sometimes called the pioneer effect

John Mashey said...

I have some reservations about this: it's a nice approach, but I have the usual questions:

1) The middle figure has two lines, and it is asserted that temperature rise/fall precedes CO2 rise/fall by 50 years, and that rules out any human infleunce (i.e., via Ruddiman plague hypothesis.)

2) When seeing precise lines, I always ask: what are the error bars?

a) CO2 line, presumably taken from the Law Dome, since that's what the
Etheridge(1996) paper is about. Graphs of that data are:
and the data itself is:

This gives dates anywhere from a few years to as much as 43 years apart (1604-1647),

b) The (reconstructed) temperature line from Moberg et al (2005), whose data is at:

c) Here is a batch of temperature reconstructions:

I.e., the Moberg is one of them, presumably with error bars, and it is by no means guaranteed to be the best approximation.

Actually, Ruddiman does have words on this:
came out in *2007*, and section 10 discusses this in detail, noting that "The sites chosen by Moberg et al[2005] are, however biased toward high-latitude and high-altitude regions..." and compares with other reconstructions.

Anyway, I make no strong assertions about anything here, but I would have liked to have seen:

a) Lines with uncertainty indicators

b) More reasoning about why Moberg's reconstruction is so clearly better than the rest that one can just treat it as precise.

c) Timeline going back to 1000AD. I always get nervous when looking at graphs with a relatively small time period.

c) Some discussion about the potential uncertainty of the box in the third figure.

Anonymous said...

"a gradient of 20 to 60 ppmv of CO2 per kelvin of global warming"

That's huge! A 200-600 ppm increase in CO2 would mean a 10 C increase in temperature.

Uh oh. I fear this is a much too simplistic estimate.

John Mashey said...

re: land use changes

I think, more precisely, we had:

1) Since human agriculture began, clearing of land for crops, albeit at a slower rate than the 1800s.

There has been interesting recent work in understanding pre-Columbian Amazon civilizations for example, who cleared lots of trees. See:;321/5893/1214 article in Aug 29 Science by Heckenberger,et al.

So did North American natives like the mound builders:

2) Hence, the other big land-use change was the waves of reforestration in areas as the natives died off from plagues.

3) Then, European settlers cleared the land again.

My family had a farm near Pittsburgh, PA since the 1840s, and I have sketches from then, showing house, barn, and a big pasture that had been cleared of forest. When the farm was sold, and no one was keeping the pasture clear, within 20 years, you'd never know there had been a pasture there, as it was again covered by dense trees.

4) The devil is in the details, but the general hypothesis that *part* of the CO2 dips/jiggles in the last millenium were due to human pandemics->regrowth->lower CO2 and then clearing->higher CO2 is of course one of Ruddiman's.

Anonymous said...

flavius said: "a gradient of 20 to 60 ppmv of CO2 per kelvin of global warming"

That's huge! A 200-600 ppm increase in CO2 would mean a 10 C increase in temperature.

That (20 to 60 ppmv) is the increase in atmospheric CO2 (due to release from sinks) per K degree of warming, not the other way around.

If the earth warms by 10K (ie, enough to release 200-600ppm equivalent of CO2), we're screwed (in a very big way) any away you look at it.

Such an increase in temp (10K) would basically require 3 doublings in atmospheric CO2 from the present concentration (assuming 3K per doubling), which means CO2 concentration would have to have reached something around 3000ppm.

The 200-600ppm added due to the CO2 released from the sinks (from a 10K increase in temp) would be the proverbial drop in the (thermometer) bucket if atmospheric CO2 ever approached anywhere near that level.

Anonymous said...

Tilo, Tilo, Tilo. There are two published sediment core studies that provide key evidence for the results discussed in the link I provided, and...

Congratulations, you found one of them!

Now let's look examine the entrails of the press release you linked:

'The best estimate from other studies of when CO2 began to rise is no earlier than 18,000 years ago. Yet this study shows that the deep sea, which reflects oceanic temperature trends, started warming about 19,000 years ago.

'“What this means is that a lot of energy went into the ocean long before the rise in atmospheric CO2,” Stott said.

'But where did this energy come from? Evidence pointed southward.

'Water’s salinity and temperature are properties that can be used to trace its origin – and the warming deep water appeared to come from the Antarctic Ocean, the scientists wrote.

'This water then was transported northward over 1,000 years via well-known deep-sea currents, a conclusion supported by carbon-dating evidence.

'In addition, the researchers noted that deep-sea temperature increases coincided with the retreat of Antarctic sea ice, both occurring 19,000 years ago, before the northern hemisphere’s ice retreat began.

'Finally, Stott and colleagues found a correlation between melting Antarctic sea ice and increased springtime solar radiation over Antarctica, suggesting this might be the energy source.'

Et voila. Enjoy your crow.

Anonymous said...

Ah Anonymous, thanks, I got it backwards... No wonder it seemed so strange.

Tilo Reber said...

Steve, Steve, Steve, I have to say that my six year old daughter gives more rational explanations for why things happen than you do - even when she's just making it up. First we have the absurdity of warm water coming from the south pole. Then we have the absurdity of the flow of that water taking 1000 years to get where it's going. Then we have the absurdity of this water retaining the heat that it picked up in the south pole for that entire 1000 years. Then we have the absurdity of this heat resulting from solar radiation, when any increase in solar radiation will be felt over the entire planet.

Eh, try again!

Anonymous said...

This might be linked to the Milankovitch theory of ice ages though (not direct solar radiation increases)?

Ie that the changes of the relation between Earth's axis direction and the orbit phase mean different areas get different amounts of sunlight at different times.

David B. Benson said...

Tilo Reber --- Not so absurd. First of all, orbital forcing in the south ressulted in some Antarctic meltwater. This results in some othr, denser water sinking, but this water was warmer than the deep water it replaced; not much, just a little.

Second, deep water residence times are now known fairly well. THe warmer deep water made its way, eventually, to the Pacific Warm Pool (where the study's data came from). This finally helped warm the surface waters in that location and globally, some hundreds of years later, the oceans were warm enough to begin expressing CO2.

So the conclusion of the study in question largely agrees wth known orbital forcings and known deep water residence times (which vary with the ocean basin being considered).

Nothing Red Queen about it at all.

Anonymous said...

Milankovitch cycles do indeed vary the "solar radiation" received at given latitudes. Insolation is the more proper term, but I suspect it wasn't used because this was a press release for non-specialists.

Tilo, I loved the argument from personal incredulity. Did you even notice that you're attacking the same material you cited in your first comment? BTW, you might be surprised by the magnitude of the high-latitude insolation increases that coincide with the deglaciations. You might also try reading the article I linked, which your comments make clear you failed to do.

Anonymous said...

David, not exactly. Read the article I linked for Tilo, since it would be nice if someone read it.

Hank Roberts said...

> within 20 years ... it was
> again covered by dense trees.

Just an aside for young readers who may not know the history -- unless you've visited one of a few rare places you've never seen a mature deciduous tree in your whole life, only the babies.

There are a couple of mature tulip poplars at Monticello.

Recall the original Eastern forest was not "dense trees" though (not to mention it had quite a bit more topsoil than nowadays).

Somewhere long ago I read -- Sigurd Olson, I think -- that the original forest averaged about six trees per acre, with their branches touching forming a continuous canopy, such that a squirrel could travel from the Great Lakes to Louisiana without touching the ground.

Very different than the "dog hair forest" we have today in most places.

Remember "Under the spreading chestnut tree"?
the village smithy stands"
The "smithy" was the blacksmith's building, not the blacksmith.

Trees come back fast, but they're not done growing and building soil around them til a few multi-century generations have accumulated.

John Mashey said...

re: trees, Hank

1) I certainly didn't claim they were mature! I actually know what mature trees look like. By odd coincidence, the oldest known living thing in the Township is a white oak known locally as "the Mashey Oak".

The farm was sold in 1976, but quoting from a "August 20, 1983 tour of Marshall Township", by Judy Oliver:

"Right in front of us as Shenot Rd. meets Wexford Run Rd. we can see the gigantic Mashey white oak towering over everything in sight...This white oak tree is the largest and oldest located in the Township so far. According to a formula used to estimate the age of trees this white oak is approximately 285 years old but the state forester who measured the tree said it could easily be 300 years old."

via GoogleEarth:
40deg38'25.24"N 80deg5'23.06'W, is the intersection of Shenot Rd and Wexford Run Rd. Judy is looking SouthWest at he tree, 40deg'19.87"N, 80deg5'28.90"W (the lighter roundish patch). The largest building is the old barn.

When she was writing this, there was pasture between her and the Oak, which stood (alone) partway up a steep hillside pasture (to North and West), which forest has reclaimed (it's a bit steep to build on).

The pasture in front of the barn is not quite so dense, but looking from the barn Southwest, by eyeball, it doesn't look much different than the woods on the other side.

Except possibly in winter, the oak is no longer visible from her vantage point, nor even from the barn [we looked]. There are too many trees in the way.

2) (From various local histories) I'm pretty sure the area to the SouthEast was never cleared for farming, although I suppose it might have been logged a little. Likewise, while I have a collection of native arrowheads found on the property, I don't think there was a lot of farming [it's hilly, tends to trees, isn't near the bigger rivers, and there are easier places to farm. Of course, Swiss farmers escaping the LIA probably thought it was heaven.]

Conditions vary, so the trees do also. I have no idea what was growing in the pasture before it was cleared in the 1800s, but I doubt it consisted only of giant oak trees. This one was rare enough that they left it in the middle of a pasture, while they cleared lots of smaller trees.

3) Anyway, the original point was that if you have land that was originally forest, and you clear it, it doesn't stay clear unless you expend effort, and when you stop keeping it clear, trees come back. [All of this was Ruddiman's hypothesis on why plagues => farmland abandonment => CO2 drop.]

David B. Benson said...

Steve Bloom --- I read it just for you.


Anonymous said...

Thank you, David. I wouldn't have wanted you to think I was being a blow-hard. :)