Monday, April 21, 2008

It's not what you don't know that gets you,
it's what you think you know and is wrong


Eli was writing another thumb sucker which required that he calculate the CO2 forcing. He used the Mauna Loa and the Law Ice dome data. A bit of Googling found that the forcing is usually given as 6.3 ln (C/Co) where Co is the mixing ratio in ppm from 1880 and C the mixing ratio at any other time. The 6.3 is the IPCC recommendation (and indeed, you can find it in a forcing calculation used at Climate Audit). The 0.67 is a reasonable climate sensitivity given in K/(Watts/m^2), you might argue that 0.75 is a better current estimate, but it really doesn't make much difference

Some time ago Eli put up a bunch of graphs with different forcings, but didn't tie the forcings to temperature. He thought it would be a good idea to complete the circle, putting CO2 forcing and global temperatures on the same scale.

The changes in CO2 mixing ratios and calculated forcings can be seen in the graph to the right. The shape of the forcings follows the temperature curve quite well. It overestimates the temperature change by a bit, but, for a BOE calculation, it shows, especially in comparison with any multiple of the solar forcing, a good agreement with the observed global temperature increase.

The mixing ratios, of course are on a different scale so the so the comparison between the two is strained, but if you graph mixing ratio vs forcing you get the correct logarithmic dependence. For example, using this rough model the CO2 forcing at 2x CO2 is ~2.9 K, while at the current value of 380 ppm it is ~ 1.1 K.

23 comments:

Barton Paul Levenson said...

Myrhe et al. 1998 found that the coefficient should be something like 5.35 instead of 6.3. For a doubling of CO2, that would produce an RF of 3.7 W m-2, and a climate sensitivity with feedbacks of 0.75 K W-1 m-2 then gives a temperature increase of 2.8 K.

Barton Paul Levenson said...

Sorry, I should have given the reference:

Myhre, G., E.J. Highwood, K. Shine and F. Stordal, 1998. "New estimates of radiative forcing due to well mixed greenhouse gases." Geophys. Res. Lett. 25, 2715-2718.

bi -- Intl. J. Inact. said...

Thanks, Eli and BPL!

Now we have quick estimates of the relative scaling of the temperature and CO2 curves, but is there any useful estimate of their vertical alignment? That is, is there any sort of useful baseline value on what concentration of CO2 corresponds to what global temperature, perhaps from paleoclimate analysis or something?

Hans Erren said...

Of course when you start twiddling with aerosols and the sun, a lower sensivity for CO2 gives a better result...
http://www.ferdinand-engelbeen.be/klimaat/oxford.html

bi -- Intl. J. Inact. said...

/me ignores yet another incoherent talking point

Dano said...

Of course when you start twiddling with aerosols and the sun, a lower sensivity for CO2 gives a better result...

Thought process:

'Oooh! Great! An aerosol paper! What journal? Um, no journal, just a website. Who cares?

Website ≠ journal paper

Best,

D

bi -- Intl. J. Inact. said...

By the way, everyone, I'm still serious about my previous request. :)

Anonymous said...

Dano,

That's what's termed a "web-jerk" when, to "prove" a point, "A" references the website of "B", who references the website of "C", who references the website of "A", who references the website of "B"....

(and they tell two friends, and they tell two friends ... and so on... and so on.)

Hans Erren said...

Hi Dano,

Expected reaction.
What was it again you wrote?

"Website ≠ journal paper"

Poor Eli...

Anonymous said...

More likely "Poor Hans".

Remind us again, Hans

How many peer-reviewed papers have you had published in scientific journals?

1? 2?

I could ask your good friend Jeff Harvey, but I thought it better to get it directly from the horse's mouth.

Anonymous said...

Bi 9:38 AM, that would be time dependent, due to the (slow) variability of the natural forcings, especially the astronomical one.

Over the past thousand years, this forcing has been very, very slowly going down. See Fig 3a in MBH99 (and text).

:wq

bi -- Intl. J. Inact. said...

Anon 7:30am:

Gee thanks... though I don't see CO2 on that graph, so it doesn't really answer my question yet.

bi -- Intl. J. Inact. said...

(oops, I mean Anon 12:47am)

PI said...

Hans,

The effects of uncertain aerosol forcings have been studied before with EBMs, going back at least to Andronova and Schlesinger , up to more recent work by Hegerl et al. (20060. Climate sensitivity estimates using EMICs are just starting to appear, such as Tomassini et al. (2007) and Sanso et al. (2008). (Well, the BERN2.5D EMIC in the former is mostly just a fancy EBM.) They usually get 2-3 C for climate sensitivity.

One key factor which can't be left out is the vertical diffusivity of the ocean, which governs the thermal inertia of the system; you can't treat it as known and fixed. At a minimum, you need to consider the joint (climate sensitivity, vertical diffusivity, aerosol forcing) estimation problem. And you need to look at ocean heat uptake data to help constrain the diffusivity, since that's so important to the observed transient response.

Usually the uncertainty in aerosol sensitivity is represented by multiplicatively scaling the aerosol forcing rather than introducing a new sensitivity parameter. Most papers have not considered solar forcing uncertainty, although at least Tomassini et al. have (along with a bunch of other forcing scale factors). I think Hegerl et al. did too.

Tomassini et al. find that to fit the temperature and ocean heat data, the indirect aerosol and solar forcings are likely smaller than the default values. This means that solar contributions to warming are slightly weaker but aerosol effects are stronger (since a weaker aerosol forcing means more warming). Their best estimate of climate sensitivity (the marginal mode) ends up being a little over 2 C, but the mean and median are significantly higher due to the long right tail. The joint mode (of all the parameters) gives 2.5 C. The probability of sensitivities below 2 C is quite low.

Hegerl et al. get a (marginal?) median of 2.6 C, and Sanso et al. get a marginal median of 2.9 C.

Dano said...

Han,

if the paper is so groundbreaking, so Galileo-like, why not share it with the world? Why not have smart people read it? Why bury it in a marginal website?

Best,

D

Anonymous said...

Dnao asks hans "If the paper is so groundbreaking, so Galileo-like, why not share it with the world? Why not have smart people read it? Why bury it in a marginal website?"

...because, of course, then it would be shot so full of holes that it would no longer even hold "Libertarian H2O" (Libertarian bonding being about 1 million times stronger than normal hydrogen bonding)

Hans Erren said...

Pielke Sr on aerosols
http://climatesci.org/2008/03/31/roger-a-pielke-srs-perspective-on-the-role-of-humans-in-climate-change/

“Humans are significantly altering the global climate, but in a variety of diverse ways beyond the radiative effect of carbon dioxide. The IPCC assessments have been too conservative in recognizing the importance of these human climate forcings as they alter regional and global climate.”

Anonymous said...

So, hans

The silence is deafening.

How many peer-reviewed papers have you had published in scientific journals?

1? 2?

or is it 0?

If nonzero, how many were on climate science -- or at least directly relevant?

Dano said...

I call Hans' handwaving tactic like 2:56 PM above by a special name: plop. He plops a big turd down, pretending that it's relevant.

This stinks up the joint, see, and distracts away from the fact he has nothing, despite the implication that the steaming mass is oh-so-relevant and refutes something. The act of Hans doing so and then carrying on in a blustering, confident way is called 'ploppedness'.

Anyway. We welcome your old tactics, Han. They are very reassuring. That is: the denialists have nothing but ploppedness, which is reassuring indeed. But your brand has the added bonus of hapless comedy as well.

Best,

D

Anonymous said...

Plop plop,
Fiz Fiz,
Oh, what comic relief it is

Anonymous said...

So, How many peer reviewed papers, hans?

What a hypocrite.

Hans Erren said...

For those who want to read some real climate science: http://climatesci.org/


BTW Dano is a plopper too:
http://home.casema.nl/errenwijlens/co2/tcscrichton.htm

yes yes, I know, that's a tu quoque ;-)
Notice also how dano changed the subject from aerosol forcing to scientific credibility ? Now thats an ad hominem, or even poisoning the well.

PI said...

Hans,

Did you notice how you changed the subject from aerosol forcings implying very low climate sensitivities, to some extremely vague unsupported allegation about the neglected importance of non-CO2 forcings?

To me, that reads pretty much like, "Well, I was proven wrong, but I'm going to scramble around to find some barely relevant quote to prove I'm right anyway."

Do you really expect anyone to take you seriously when you cite random web sites to disprove the climate sensitivity of CO2? These things have been studied in the literature before, you know. Why don't you cite it? Is there some reason why you prefer not to read what climate scientists publish?

At the very least, if you think your random web site is correct, you should contrast it to the existing literature to highlight the point of departure. Instead, you have to rely on others to inform you that your web site study has been done in a far more professional manner many times over, and does not come up with the conclusion you were hoping for.