Everything Dr. Rabett said about the Knorr paper, with the exception of how to spell Dr. Canadell's name, is altogether right and true and clear and proper. This is not my opinion so much as it is settled scientific consensus that there is a controversy. It is a closed question that there is an open question. To wit:

There is a very simple way to put it:

We know the amount of CO2 emitted by us per year (pretty well) Call it X.

We know the amount of this CO2 that stays in the atmosphere (the rest goes into the oceans and the biological bits of the land). That is, for reasonable purposes X/2 or 50%.

That means that 50% of the CO2 that we emitted each year remains in the atmosphere.

The question is whether the fraction is changing. Maybe only 48% is absorbed and 52% remains in the atmosphere.

Knorr says the fraction is not changing. Canadell says the fraction remaining in the atmosphere is increasing.

Canadell is really serious trouble. Knorr is only serious trouble.

That's all folks.

hth

- Ray Pierrehumbert

## Saturday, January 2, 2010

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## 5 comments:

There doesn't seem to be any reason at all to expect the airborne fraction to remain constant, and the fact that it does seems to be an approximate coincidence (between the rate of growth of the anthropogenic CO2 production - the denominator of the airborne fraction - and the rate of growth of the absorbed amount). The net absorbed amount is a function of the atmospheric concentration, not of its rate of change.

The fact that some soi-disant sceptics are raising Knorr as "all you need" to dismiss AGW tells us more about them (i.e. that they are fundamentally ignorant of the subject, and not particularly interested in learning) than about atmospheric CO2.

Nick, I agree.

In fact, all Knorr showed was that any trend was not so enormous as to be confidently detectable by his methods. Indeed, in a Bayesian sense, Knorr agrees with Canadell; the trend is more likely to be in the adverse direction than the favorable one on his evidence. Knorr certainly isn't claiming that there's some fundamental reason that the fraction remain constant.

Nevertheless, if the various people babbling about this paper all understood at least as much as Eli said, the public discussion would be much more useful.

Read science?

I thought it was settled? :-)

Maybe someone more knowledgable than I can answer a different question than whether or not the fraction has remained constant.

Once upon a time, I spent a lot of time worrying about technology trend forecasts, and especially of rations, like CPU speed vs DRAM access time, or DRAM cost/bit vs disk cost/bit. Quite often, the real issue was to predict *inflection points* in trends or ratios of trends ... and it was sometimes hard, and even the best could miss.

SO: assuming that the airborne fraction has been ~constant, can people summarize what's known or not about likely parameters that would induce inflection, specifically, the "bad inflection".

Ocean absorbtion depends on deep overturning circulation and surface saturation.

The latter is unfavorable: warm water holds less CO2. Some skeptics like to propose this as the main mechanism for the carbon variation over the glacial cycle but this seems to be wrong.

The former is possibly unfavorable, as increasing cold freshwater reduces the density of cold water and slows deep overturning.

No refs off the top of my head for this.

Biotic uptake of CO2 relies on CO2 fertilization of forest growth and net advance of forests into new territory. Eventually, other limits (water, nutrients, availability of land at high latitudes) kick in. Also forest mortality due to invasive species cuts the other way.

Inez Fung is a good person to start with on this one.

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