Friday, June 25, 2010

What Evidence Would Support AGW?

A few days ago I asked Roy Spencer, the well-known AGW-skeptical scientist at the University of Alabama at Huntsville who keeps the UAH their satellite records on temperature, what would convince him of a human influence on climate.

Here's his response -- quoted with permission -- not exactly reassuring:
There is no unique fingerprint of AGW. Since it is a "radiative forcing" (radiative energy imbalance of the climate system), it cannot be distinguished from circulation-induced changes such as a decrease in albedo of the Earth (e.g. a decrease in cloud cover) or an increase in atmospheric water vapor or high cloud cover

The AGW crowd either do not believe these changes occur, or they do not know enough to realize that is what they are implicitly assuming.

Some will claim stratospheric cooling IS a signature of increasing CO2, which indeed is possible, but the stratosphere is much simpler in behavior than the troposphere, where clouds and other moist processes have such a huge influence.

So, I do not believe there is any way to recognize AGW...short of global temperatures increasing another 5 deg. C. That would probably make even me a believer. :-)

It has occurred to me that it is possible this debate -- and all the ancillary junk that goes along with it -- will never end. Think about it: suppose we drastically refurbish society and get all of our future energy from renewable, non-carbon sources. It's the year 2080 and temperatures are the same as they are today.

Advocates will argue that it was the switch to non-C energy sources that saved the day. Skeptics will argue that CO2 was not such a big problem all along and we spend $5T for nothing.

Hopefully 2080's science will be advanced enough to distinguish between these two scenarios. But I'm not sure that's a given.

(PS: If you're reading this in the year 2080 AD, PLEASE leave a comment.)

12 comments:

Dano said...

It'll never end with the dead-enders and the ~12% of society for which absolutely nothing will change their small minds.

There is a voting majority for action. There is no reason to delay any longer to assuage the small minority of dead-enders. There is a majority. Act. Who cares about people who refuse to change their minds on this issue?

Fuggem. Act. There is a majority in this Plutocracy whose ruling class will lose profit if their pollution is curtailed.

Best,

D

David Appell said...

Dano wrote:
> Who cares about people who refuse
> to change their minds on this
> issue?

Well... because they too are going to have to pay their share of the $X trillion to remake society, where X ~ 2-5 and maybe 10, or even more.

$10T = $30,000/person

How would you feel about paying another $5T for, say, a middle-east war that conservatives insist is necessary to insure our supply of oil?

mike said...

Most AGW-skeptics are aparantly conservatives and libertarians. If they come to believe global warming is real and needs to be opposed, they're effectively admitting a need for government programs which are likely to be expensive, intrusive, and lengthy. Most conservatives would find an appendectomy without anesthesia to be much less painful.

Brian Schmidt said...

There are still a few ozone-hole denialists out there, some of the same people denying AGW, and we're making them pay the societal costs along with everyone else to switch to alternatives. And I'm okay with that.

Back to stratospheric cooling - I'd think a simpler system at that atmospheric level would make attribution easier. I don't know what Spencer means, then.

Anonymous said...

"Hopefully 2080's science will be advanced enough to distinguish between these two scenarios. But I'm not sure that's a given."

Current science has already resoundingly answered that. The question of attribution is one of such primary importance that there are entire books and hundreds of research papers attesting to the answer. Yes, there is a small margin of error (which is what most of the research is about), but overall it is as close to a fact as science can say about pretty much anything that anthropogenic CO2 has caused an unambiguous warming signal in our climate. Disputing it is now simply wishful thinking or willful ignorance.

EliRabett said...

Spencer's answer about stratospheric cooling pretty much shows that he is going la la la.

To quote:
-----------------------
Some will claim stratospheric cooling IS a signature of increasing CO2, which indeed is possible, but the stratosphere is much simpler in behavior than the troposphere, where clouds and other moist processes have such a huge influence.
-------------------------

The question is, is stratospheric cooling a signature of increasing CO2, not whether it is a signature of global warming. We KNOW

a. The stratosphere is cooling right where theory expects it to cool if CO2 increases

b. CO2 is increasing.

Which yields c.

c. Spencer is a clown. The reason he avoids the issue is that the reason the stratosphere cools is less radiation is coming from the troposphere in the CO2 bands because there is more CO2 at lower levels. Because of this, the level at which CO2 radiation can pass from the troposphere to the stratosphere is higher and cooler. The cooler, the less radiation in the CO2 bands. It has NOTHING to do with clouds.

rhhardin said...

The AGW crowd doesn't distinguish curve-fitting from science.

You can fit any data with anything with lots of parameters.

You have to avoid parameters that aren't a priori.

Say by solving actual physics equations.

Maybe it's that the crowd doesn't recognize parameters, or maybe that they don't realize what a surfiet of parameters does.

David Appell said...

rhhardin said...
rhardin wrote:
> The AGW crowd doesn't
> distinguish curve-fitting
> from science.

You've claimed this before. It's bullshit. GCMs are certainly not curve-fitting.

> Say by solving actual
> physics equations.

Have you ever actually analyzed a GCM in detail? Several groups now publish the foundations of their models. You might begin at http://www.giss.nasa.gov/tools/modelE/modelE.html#part3

rhhardin said...

The link is full of parameters and coarse grids.

Do you realize what a parameter is?

Look up Kalman filtering, which is just plain old least squares taking account of variances, but formulated in a way that makes it plain that the process exactly duplicates building a model to match data.

Your model will have physics bits all over the place, and parameters to piece them together.

The Kalman process determines the values of the parameters from the data, an unexceptional bit of work, except it can also manifestly be interpreted as plain old curve-fitting, which it is.

A single equation from first principles, on the other hand, one which we can't solve unfortunately, has practically no parameters to be determined, and so actually gets verification from matching data.

A pieced-together model always matches the data if you determine the parameters to match the data, but has no predictive or explanatory value.

It is that that I'm claiming the AGW crowd does not see the significance of. Certain kinds of scientific-looking work, if pieced together, wipe out the science.

Model builders have been around for decades. Now they've taken charge.

David Appell said...

rhardin wrote:
> The link is full of parameters and > coarse grids.

Yes, these are essential.

And they are *not* "curve-fitting."

Curve-fitting is something like Newton's method of least squares or principal component analysis.

Nothing like that takes place in GCMs.


"Parametrization" is simplification. It's like using the ideal gas equation in 10th grade -- of course, PV=nRT does not describe a real gas at all points and at all times.

It is an idealization and approximation that allows you to do some calculations and make some progress.

There are always uncertainties involved. That's why GCMs give a *range* of (say) future temperatures, 2.5-4 C or so.

All such physical calculations have such parametrizations and simplifications. It is the way of physical models.

You, neighter, can solve the underlying physical equations (Navier-Stokes, Maxwell, etc) in such an extremely complex situation without approximations.

If so, show us.

rhhardin said...

Curve-fitting is something like Newton's method of least squares or principal component analysis.

Nothing like that takes place in GCMs.


You just don't recognize it.

Eg coarse grids require at minimum some way to put in viscosity, which is hidden in flows at shorter scales; that's a free parameter and it gets set by the data, along with a thousand other joinings of separated physical processes.

As I say, Kalman makes explicit what the best way is to adjust parameters, and it amounts to least squares. It matches what you'd do with common sense, just formalizes it. The idea makes visible how parameters give you curve fitting.

On approximation, consider aerodynamics, from which the expression "pushing the envelope" comes. They know when they're predicting outside where they have data to verify the model - they know where the envelope is - and take steps to get data there before they use the model.

AGW has no such envelope.

PV=RT is well explored and the envelope is well known. In a doubtful case, you'd look further.

Anonymous said...

So, in laymans' terms he's saying that going from doubled windows to tripled windows doesn't improve the energy efficiency of a house?
Some housebuilders might be of different opinion.