28 November 2009

Anthropogenic Global Warming

Seems like a good time to revisit anthropogenic global warming: what do we know, what can we assume, and what can we do it about it.

Anthropogenic global warming is a series of nested propositions:

1. The global temperature is rising. This is the heart of AGW, and until this week, it was the real consensus of informed scientists. After the CRU leaks, it turns out that we can't even be sure that the globe has been getting warmer over the last century. Other questions are, what is "global temperature" and is it even relevant. Maybe we should worry about peaks and not averages. Maybe we should worry more about temperatures at the poles or at the equator rather than global averages. Because it turns out that the only good temperature record we have lasting longer than decades is for particular spots in the US and Japan and some of those will have changed due to local urbanization (and in at least one case, because someone pointed an air conditioner dump vent at the thermometer). Of course, at some point we all agree that the globe's gotten warmer; we used to be in the little ice age, which ended about 1880, so the world has clearly gotten warmer since then. Of course, that's been a good thing, leading to the need for proposition 2.

2. Rising temperatures would be bad. In fact, the experience of mankind is to the contrary. Rising temperatures are good. We get more crops, we gain arable land, fewer seniors drop dead shoveling snow, etc. So AGWists need to posit large increases in temperature that push us past a tipping point at which civilization is devastated (or, at least, Bangladesh is under water). We can't get there through CO2 alone, though, even though AGWists put a lot of time into arguing proposition 3.

3. Carbon dioxide causes higher temperatures. This is probably true. Carbon dioxide is a greenhouse gas in that it absorbs sunlight and emits heat at levels higher than the atmosphere generally. But the direct effects of carbon dioxide on temperature are well understood and relatively mild; about one degree for every doubling of CO2 in the atmosphere. Since we're unlikely to double CO2 even twice from this point on -- even as India and China industrialize -- that really isn't going to get us over the tipping point, so

4. Carbon dioxide warming will be amplified by positive feedback mechanisms -- that we've never seen, can't describe and don't understand. The historical evidence seems pretty clear: temperature increases have been followed by atmospheric CO2 increases but never preceded by them. Even worse for the AGWists, we do understand at least two negative feedback mechanisms: more CO2 leads to more plant growth, which, by reducing the Earth's albedo, cools temperatures be reflecting more energy into space; and rising temperature leads to more cloud cover, which reduces Earth's albedo, etc. Basically, AGW's appeal to science just breaks down here, even though positive feedback is absolutely essential to the AGW as disaster scenarios.

5. Industrialization, which leads to release of CO2 into the atmosphere, causes AGW. This is actually more problematic than it appears, because industrialization also leads to the emission of particulate air pollution and other gases, like sulfur dioxide, that cause atmospheric cooling. Do the traces of CO2 we release into the atmosphere overpower the traces of SO2 we release into the atmosphere? Your guess is as good as the CRU's. At least one AGWist theorizes that the reason there hasn't been any warming over the last 10 years has been because of the increase in SO2 pumped into the atmosphere by India and China. That, of course, implies that the clean air act threatens to destroy the world.

6. Global warming is bad because it's anthropogenic. Lot's of AGWists seem to argue that we are obliged to do something about global warming because it's anthropogenic. But what difference does that make? If global warming were natural but disastrous, should we let it? If it were man-made but good (a real possibility, of course) should we stop it just because we're changing "nature?" This (and the continued opposition to nuclear power) is where it becomes clear that AGW isn't scientific at all for many proponents; rather it is political/religious/spiritual.


Francis T. Manns, Ph.D. said...

Climategate Foretold...
“• What is the current scientific consensus on the conclusions reached by Drs. Mann, Bradley and Hughes? [Referring to the hockey stick propagated in UN IPCC 2001 by Michael Mann.]
Ans: Based on the literature we have reviewed, there is no overarching consensus on MBH98/99. As analyzed in our social network, there is a tightly knit group of individuals who passionately believe in their thesis. However, our perception is that this group has a self-reinforcing feedback mechanism and, moreover, the work has been sufficiently politicized that they can hardly reassess their public positions without losing credibility.”
AD HOC COMMITTEE REPORT ON THE ‘HOCKEY STICK’ GLOBAL CLIMATE RECONSTRUCTION, also known as The Wegman report was authored by Edward J. Wegman, George Mason University, David W. Scott, Rice University, and Yasmin H. Said, The Johns Hopkins University with the contributions of John T. Rigsby, III, Naval Surface Warfare Center, and Denise M. Reeves, MITRE Corporation.

Harry Eagar said...

7. No matter what, the global temperature will change. It has never stayed the same.

OTOH, it has never varied by much, either.

Bret said...

Though I'm not an expert, I think there are a couple of minor misstatements in the post:

"Carbon dioxide is a greenhouse gas in that it absorbs sunlight and emits heat at levels higher than the atmosphere generally."

Not exactly. CO2 is relatively transparent to Short Wave Radiation and relatively opaque to Long Wave Radiation. The greenhouse effect occurs because SWR (light) from the sun is converted to LWR (heat) when it hits the earth's surface. The SWR passes through the atmosphere unimpeded by CO2 but the LWR is not radiated back through the atmosphere as easily making the surface temperatures higher than they otherwise would be.

"...more CO2 leads to more plant growth, which, by reducing the Earth's albedo,..."

I think you're using the term "albedo" incorrectly. High albedo implies high reflectivity (an albedo of 1.0 means all light from the sun is reflected) so reducing albedo would imply higher surface temperatures.

"Do the traces of CO2 we release into the atmosphere overpower the traces of SO2 we release into the atmosphere?"

There's an issue of timeframes. My understanding is that it takes far, far longer for CO2 to be reabsorbed than it takes for SO2 since SO2 is very water soluble (basically it falls out of the atmosphere in "acid rain"). So an AGW'er will claim that while the SO2 is balancing CO2 right now, the accumulation of CO2 (and resulting warming) will eventually overwhelm SO2 emissions.

The real issue IMHO is that like clouds, the impact of particulates and aerosols on temperature is poorly understood and even more poorly modelled. The warming seen from 1970-1998 could well have been the result of reduced particulates and aerosols (or increased particulates such as black soot in China).

Brit said...

Your point 6 is v good - I can't recall seeing it expressed so succinctly before, but it's obviously right.

Harry Eagar said...

It isn't excluded, either, that fluctuations in climate (which we know exist) can be explained almost completely by orbital geometry.

The solar physicists up the road from me (or some of them) think so.

I might add:

8. The amount of knowledge gained per dollar expended on climate research may be close to the lowest return on investment of any research program since the 5th Generation computer.

Hey Skipper said...

It might be worth mentioning that the Anchorage Daily News, which carries at least three hysterical climate change articles per week, has not reported one word about Climategate.

A little googling indicates that the NYT has been nearly as silent.

My dismissive attitude towards the MSM is starting to verge towards outright hatred.

Peter Burnet said...

By chance I've been engaged in some discussions on AGW recently on two leftist blogs, one hard, one softish. It's a minefield of bile and insult, although I was quite proud that I was able to establish enough credibility to be dismissed as a mere fibber rather than an outright liar. You can have five postgraduate degrees in climatology, but you are still a science-denier if you challenge the IPCC.

One proof of #6 is that any suggestion that things may not be so bad is met with a chorus of disdain and contempt rather than hope at good news. And what really drives them apoplectic is any suggestion that the problem can be remedied technologically, as if such amounted to advocating some kind of massive fraud on Mother Earth.

Here, courtesy of one of the head honchos at East Anglia, is an honest description of what is behind a lot of it. We seem to have entered an era of scientific postmodernism where the narrative trumps the evidence. Was it always thus?

Harry Eagar said...

He must be awkward at high table.

What if there's a fifth myth, the Twainian: everybody talks about the climate, but nobody does anything about it.

I don't envy you your venture in AGW-world. Whichever side you chose to engage with on this subject, you're going to have some mighty unpleasant allies.

David said...


I'd be interested in links to some of these websites where you see off the forces of darkness.

Peter Burnet said...

David, check your e-mail later today.

I've just stumbled on another leftist thread on naturopathy, in which many seemingly non-technical, everyday folks weighed in. Quite the brouhaha, of the sort we see from time to time on chiropractic. But what was interesting was the nature of the argument. Are naturopaths bad because they are dangerous? Because they are ripping gullible people off? Because they don't know what they are talking about?

None of these. The problem with naturopathy is that it is not "science-based".

Harry Eagar said...

See here.

There are a LOT of crazy people standing in line with you at the checkout stand.

David said...

Everyone's crazy but you and me, Harry, and sometimes I wonder about you.

joe shropshire said...

All sound points, very interesting. Now let us take a step back, and propose a proper scientific test of AGW. We know that Cohen is either still in grad school or else is doing his postdoc. So there is a job interview at some point in the future, and there is this post on this blog. These make for a climatological controlled experiment with three possible outcomes:

(1) Cohen gets his share of interviews, one of which leads to a tenure-track position. AGW is completely discredited. If AGW can't keep the guy who wrote this post from finding employment, then what practical use is it?

(2) Cohen gets no interviews at all. Inconclusive. He could just have a weak resume.

(3) Cohen gets his share of interviews, but no job offer emerges. AGW is confirmed.

Nature is boring. People are interesting, in the same sense that watching a film of a pack of chimpanzees as they hunt down and kill and share the flesh of a small tree-dwelling monkey, is interesting. Good luck with that job interview.

David said...

It's a bad test, because I'm in Management and will be interviewing with business schools. The faculty is still liberal, but at least somewhat aware that it is theoretically possible for conservatives to not be entirely evil.

Now, if I were in a field were AGW was critically important, like English literature....

Harry Eagar said...

I have just begun reading AGW uber-alarmist Stephen Schneider's autobiography, "Science as a Contact Sport," and he says that his position has, at times, "threatened my career."

So there appears to be more than one opinion about what gets you up in the academy.