Sunday, August 04, 2013

Andy Dessler on Climate Sensitivity

Mom Rabett told Eli that there is no need to make the rubble bounce when you have friends who will do the job for you


Anonymous said...

Merchant of doubt?

"We just have no idea what the forcing really is."

"Maybe it's one degree. Maybe it's two degrees. Maybe it's four degrees. Maybe it's eight degrees."

(Maybe it's zero degrees?)

There is real trouble trying to assess water vapor feedback from the tropics without entertaining the idea that dynamics may control both temperature and humidity.

The other problem with Dessler is that water vapor feeds back very quickly in climate terms - it's already part of the observed trend. So too is the amount of ice albedo feedback corresponding to the Arctic sea ice decline.

Ironically, Dessler claims those declaring a lower future sensitivity depend on a negative feedback ( cloud albedo ) at the same time, Dessler himself invokes an "unknown" negative forcing ( aerosols ) to explain away the fact that observations tend toward a lower sensitivity.

I will concur with Dessler ( and Hansen ) that we just don't know what earth's energy budget is well enough to actually make these assessments.


Monty said...

Low sensitivity is also unlikely given the nature of past climate.

Martin Vermeer said...

we just don't know what earth's energy budget is well enough to actually make these assessments

All the more amazing then your calm confidence that the true value is small... gotta have faith, eh?

Jeffrey Davis said...

If climate sensitivity were very low, we wouldn't have seen the huge swings in temperature in the past. How could there be glacial retreat since Milankovich forcing is an order of magnitude less than from our increase in CO2.

EliRabett said...

The water vapor feedback is not only fast, but because of its speed, local which allows us to get a good grip on its magnitude. The cloud feedback is a lot more slippery.

While it is always possible to invoke some mysterious deus et machina to control temperature and humidity and carrots, in the absence of detail, this is merely handwaving.


After scores of published studies,

( 1-f)

isn't exactly converging.

Hank Roberts said...

Any cherries ripened since 2008?

Martin Vermeer said...

Not to worry Russell, I promise that still this century we'll have (1-f) nailed really precisely...


Show us the data points you have in hand, Hank- none of the four studies I've seen since 2008 are outliers.

Anonymous said...

Whatever else may be true, Dessler does not understand "order" (of magnitude)

1 and 8 have different "order" ("0" and "1", resp)

Albatross said...

Hello all,

Maybe Previdi et al. (2013, Quart. J. Royal Meteor. Soc.) will bring matters into focus (it is open access, so go and have a gander).

"Traditionally, only fast feedbacks have been
considered (with the other feedbacks either ignored or treated as forcing), which has led to estimates of the climate sensitivity for doubled CO2 concentrations of about 3◦C. The 2×CO2 Earth system sensitivity is higher than this, being ∼4–6◦C if the ice sheet/vegetation albedo feedback is included in addition to the fast feedbacks, and higher still if climate–GHG feedbacks are also included. "

Not happy news...yet we still have dissenters/obfuscators (aka the Pielke clan).

Anonymous said...

NOAA keeps and index of the greenhouse gas forcing ( consistent with IPCC theory )

If one correlates observed surface temperature with
greenhouse gas forcing,

one will likely arrive at a correlation similar to this.

If one then multiplies the result ( 0.44 K per W/m^2 ) by the forcing of a CO2 doubling ( 3.7 W/m^2 ),

one will likely arrive at a transient sensitivity to this.


Brian Dodge said...


Your analysis presumes instantaneous equilibration. Do you think that if anthropogenic CO2 emissions were halted, that -
1. the summer minimum Arctic Sea Ice extent would stabilize at 3.6e6 +/- 0.56e6 km^2?
2. The ocean would be the same temperature in 100 years as it is today?
3. The loss of ice from Greenland would change from 1000Gtons per year to zero?
4. The decline in glacier mass/volume would halt?
5. The decline in NH spring snow cover wold stop?
6. That the increase in albedo from the desertification of croplands will provide more negative feedback than release of soil carbon provides positive feedbacks? "At the global scale, lagged correlations between temperature and carbon dioxide growth rate were found, indicating modulation by biogeochemical feedbacks."

Susan Anderson said...

Brain Dodge,

Another amateur musing:

7. Will the seriously disrupted global circulation go back to normal and stop giving us stalled weather patterns? Will the Hadley/Ferrell/Polar cells stop merging?

Anyone inclined to educate me as to how to phrase this better and anything else at a very low level I could absorb, I'd like additional input. I have followed Jennifer Francis.