Friday, August 19, 2016

"A jetliner is just aluminum wrapped around a theory."

Piers Sellers, an upper-level official at NASA, wrote an interesting essay for the New Yorker this week: "Space, Climate Change, and the Real Meaning of Theory."

He points out that we design bridges based complicated models that apply Newton's laws of motion and the observed properties of materials, and these bridges are build and they (rarely) fall down.

We build airplanes based on the physics of fluid mechanics and the dynamical laws of motion and properties of substances, and they are rolled out of hanger, pointed down the runway, and take off.

And in exactly the same way, we project climate based on elementary laws of physics proven a century or more ago -- the Planck Law, the Stefan Boltzmann law, the measured absorption properties of gases. And many other laws of physics that represent the real world. Just look at all this physics.

Manmade global warming isn't rocket science. I mean, Arrhenius put the pieces together in the late 1800s, though not quite prefectly. Lots of improvements and additions have come since. This is basic, even obvious stuff.

All climate models ever constructed show warming from human emissions of greenhouse gases. Given CO2's role in the greenhouse effect, it is hardly surprising that 45% more CO2 in the atmosphere would cause more warming.

It'd be far more surprising if it didn't.


It is perfectly legitimate to make predictions based on observations combined with well established physical laws. That's how geologists discovered tectonic plates. How Neptune was discovered. How the atomic nucleus was inferred. And so on.

There is no experimental proof that smoking is harmful -- it's unethical to do such experiments, and impractical -- yet we know that it is. This conclusion isn't going to be reverse next year, or in 20 years.

 Sellers writes:
Climate models are made out of theory. They are huge assemblies of equations that describe how sunlight warms the Earth, and how that absorbed energy influences the motion of the winds and oceans, the formation and dissipation of clouds, the melting of ice sheets, and many other things besides. These equations are all turned into computer code, linked to one another, and loaded into a supercomputer, where they calculate the time-evolution of the Earth system, typically in time steps of a few minutes. On time scales of a few days, we use these models for weather prediction (which works very well these days), and, on longer time scales, we can explore how the climate of the next few decades will develop depending on how much carbon dioxide we release into the atmosphere. There are three items of good news about this modelling enterprise: one, we can check on how well the models perform against the historical record, including the satellite data archive; two, we can calculate the uncertainty into the predictions; and three, there are more than twenty of these models worldwide, so we can use them as checks on one another. The conclusions drawn from a careful study of thousands of model runs are clear: the Earth is rapidly warming, and fossil-fuel burning is the principal driver.

But theories are abstract, after all, so it’s easy for people to get tricked into thinking that because something is based on theory, it could very likely be wrong or is debatable in the same way that a social issue is debatable. This is incorrect. Almost all the accepted theories that we use in the physical and biological sciences are not open to different interpretations depending on someone’s opinion, internal beliefs, gut feelings, or lobbying. In the science world, two and two make four. To change or modify a theory, as Einstein’s theories modified Newton’s, takes tremendous effort and a huge weight of experimental evidence.

And this is where politics and science can find themselves at cross purposes. In many political discussions, climate science gets treated like family planning or tax restructuring. When it comes to these social issues, convictions or personal views count for a lot, and rightly so. But the climate issue, and the business of climate prediction, is different. The changes we’ve seen over the past hundred and thirty years are incontrovertibly documented: they are facts.
I think the prediction of manmade warming, based on our emissions and the known laws of physics, is perfectly legitimate and adequate to prove AGW. Sure, you have to get into some of the weeds to get all the details, but physicists have been doing this for decades and have the radiative transfer down pat.

I'm not sure how many people realize this, but the role of CO2's radiative effects (and the other main GHGs) is the best know part of climate science. Because it's the most amenable to a standard treatment by fundamental physics.

So deniers thinking that someday CO2's role in climate change is going to be negated based on some new observation or some future pause or something else are very wrong and very lost. The uncertainities all lie elsewhere, especially in the details of clouds and in the details of the carbon cycle and how it will change in the future.

So the arguments CO2 looks increasingly naive and foolish. CO2 from fossil fuels will never go back to being an innocent substance. Ever.

On the contrary -- future generations will look back on us as dumb greedy idiots for thinking we could dump massive amounts of CO2 in the atmosphere and expect there would be no result.

We may (and probably won't) zero in on the exact value of climate sensitivity -- too may uncertainties in too many variables. But knowing it's 2°C or more is perfectly sufficient to know we have a big problem.

Piers Sellers didn't have room, or the audience, to point out that this isn't all theory. There are many -- increasingly many -- observations that verify the vital parts of AGW theory -- the enhancing greenhouse effect, the radiative forcing of CO2 (which agrees with the predictions of climate models), the observed ocean warming and energy balance of the planet.

And more. There is so much evidence from so many different angles that, like the health effects of smoking, the result is surrounded by evidence and cannot escape it.

But I'm probably repeating myself.


David in Cal said...

There are some questionable comments in Sellers' article. Here are a few:

The facts of climate change are straightforward
Some of the fact are straightforward, e.g., that the planet is warming and CO2 emissions are a cause of the warming. Other facts, such as the effect of various feedbacks and the true value of sensitivity, are not straightforward.

we can check on how well the models perform against the historical record, including the satellite data archive
Agreement with the historical record is weak confirmation, since the models were based on the historical record.

we can calculate the uncertainty into the predictions
Variability in the historical record doesn't measure the uncertainty of model assumptions and the uncertainty due to factors not reflected in the models.

there are more than twenty of these models worldwide, so we can use them as checks on one another.
There are many models in addition to the ones used by the IPCC or by NASA. Sellers sees models confirming each other because models with unusually high or unusually low predictions are ignored.

David Appell said...

The "the true value of sensitivity" -- though such a thing doesn't really exist -- is not a "fact" that goes into climate models, it is an output. So are feedbacks -- they are emergent consequences of the laws of physics.

The basic facts of climate change are straighforward: the Earth emits infrared radiation, and CO2 and other GHGs absorb it.

Of course the models are base on the historical record! What else should they be base on -- the climate of the planet Tatooine in Star Wars?

However, the models do also describe Venus and Mars.

All calculations in physics have an associated uncertainty, based on the uncertainties of the data that go into the calculation. Those can be calculated, or evaluated by model spread.

What models are ignored based on their results?

David in Cal said...

This link includes some models predicting cooling.

A National Geographic report says, "If the warming were to go beyond 6-to-7 degrees Fahrenheit (about four degrees Celsius), she says, as predicted by some climate models..."

Sellers said we can use the models as checks on one another. If I understood him correctly, he's saying that the models gain credence because they produce consistent results. However, the examples here show that model results vary.

I think only some of the uncertainty in a model can be calculated from the uncertainty of the data. I am not sure what's meant by evaluation by model spread. But, my point is that a model is a simplified respresentation of reality. We cannot be sure how much uncertainty is due to the things not in the model. This is something like the unknown unknowns.

E.g., in the case of global warming, some scientists believe there's a "tipping point", beyond which warming will speed up and/or become irreversible. Other climatologists have not endorsed the idea of a tipping point. So the existance or non-existance of a tipping point as well as its exact nature are sources of uncertainty.


David Appell said...

"This link includes some models predicting cooling."

Those aren't models.

They're just people spouting off.

Has even one of them published a real paper in a real journal?

David Appell said...

"E.g., in the case of global warming, some scientists believe there's a "tipping point", beyond which warming will speed up and/or become irreversible. Other climatologists have not endorsed the idea of a tipping point. So the existance or non-existance of a tipping point as well as its exact nature are sources of uncertainty."

And every such claim -- ALL OF THEM -- emphasize that those aren't prediction, they're possibilities.

And they are.

David Appell said...

"I am not sure what's meant by evaluation by model spread."

You take a bunch of models -- an emsemble -- and graph their results. That's the spread.

Reminder: climate models do not start in a known initial state.

David in Cal said...

You're right, David. The link I provided doesn't list actual models (except maybe for the Russian space scientist). Here's a site that does link to actual climate models that predict very low sensitivity.

Now, I'm not saying that these models are correct or how much credence they deserve. I'm criticizing Sellers' reasoning. One reason he has confidence in the models is that he thinks the various climate model all give fairly consistent results. But, that's not the case when one looks at the full gamut of climate models. It's just that he doesn't know about the models that differ greatly from the consensus view.

Re: the tipping point. As you say, that's not a prediction, it's a possibility. Nevertheless, that possibility is a source of uncertainty in the models. And, this uncertainty cannot be calculated.

As you point out, the models are based on the historical record. As I understood Sellers, he was impressed that the models did a good job of reproducing the historical record. I don't think that's strong evidence one way or the other. Correctly predicting the future would be stronger evidence.


David Appell said...

David, don't give me a fucking link to a stupid-as-shit blog like no tricks zone.

It's very telling that you can't quote science and have to link to assorted idiots like Joe Bastardi and dumb denier blogs like Pierre Gosselin.

David Appell said...

David: I'm just fucking sick of dumb idiots like you who link to every denialist idiot on the planet as a way to try and disprove AGW.

Nothing you have ever written here -- NOTHIHG here, David, EVER -- has ever been worth a damn. It's all just the usual dumb-as-fuck denialist shit.

It's not science.

Same goes for Richard.

Frankly I wish you'd just take your rank stupidity and go somewhere stupid like WUWT where you belong.

Your posts here have been nothing but a huge waste of time. Richard's too.

If I was a denier I'd ban you from my blog as a way to enforce ideology. But I'm not afraid like that, so you can post whatever stupidity you want here. And I will keep pointing out what an idiot you and Ricard are.

Get lost.

@whut said...

Excellent post. You hit the nail on the head in that the role of CO2 is probably the best understood part of the science.

What "David in Cal" said "Correctly predicting the future would be stronger evidence." has got to be the non-sequitor fallacy of the ages. The trap they want to set is for you to make a prediction for 20 years down the line so they can then wait for it to pan out (or not) while they maintain the status quo. Not willing to take that bait.

... But really, who cares about what DavidInCal has to say? What I think is important is to go after the credentialed contrarians such as Salby and Lindzen and rework their research findings. Their recent contrarian research is easy to debunk, but going back further, I think their early research is up for more scrutiny.

Layzej said...

I don't think you can claim to be waiting for the results of the projections. Figure 7 in Hanson's 1981 paper projected a rise of about 0.6C in 2016 relative to 1976 - for a model sensitivity of 5.6C.

For a sensitivity of 2.8 he projects about 0.5C and just under 0.4 C if sensitivity is 1.4.

If you fit a linear trend between 1976 and today you find a rise of 0.73C.

35 years later we're worse off than that "alarmist" Hanson had anticipated in his worst case projection.

So what are we waiting for?

Windchasers said...

This link includes some models predicting cooling.

DavidInCal, do you vouch for these models? Meaning, you understand the methodology behind them and can vouch that the math and physics used therein are sound?

If you want to pick just one, I'll be happy to go through it with you and examine its merits.

On the other hand, if all you want to say is "here are 50 models, and I don't know if they're right or not", then meh. I can come up with 50 people saying vaccines cause autism, too. Doesn't mean they're right.