Monday, 24 October 2011

Climate Change

The Ascent of Man is not just a species-wide phenomenon. The joy of science is that the whole species progress by means of individuals progressing. It is the defining characteristic of a rational scientific mind to despair at its past self. A scientist corrects the errors in her worldview, over time her map looks more and more like the territory. Errors only get smaller. I'm annoyed at my past self, just as my future self will be annoyed at me. One error my past self made I dont get annoyed at, because I dont think it was unreasonable. Though I have now corrected it in my map, it should not be hard to imagine why others should not have done so yet. This phenomenon tells us something wider about the danger of a little information and science communication.
For many years, indeed until very recently, I did not accept the existence of anthropogenic global warming. I now do. I want to explain why this change happened, and why I dont think my past self was deceiving himself or in any other way guilty of a major moral error.

If this is true, then a change in rhetoric is needed in people who wish to convince others of the reality of this global danger. We cannot, to my mind, say that "denialists" are deliberately lying, or that they chose to accept something false for political reasons. The rank and file of those who do not accept AGW are like many complementary medicine patients, guilty of laziness for not having considered the evidence in enough detail, but not actually evil. Of course, the many who have done the work, including the many scientists who publicly support campaigns against AGW-based policy are far more like the quacks, they've done enough to know better, they are actually doing something wrong.

Ok, so, why did I fail to believe. Why wouldn't I accept what I now do? Well, consider the evidence. Young me did. He read all the major arguments, he scoured blogs and websites on the topic. And you know what, he found some bullshit arguments. I want to go over them, explain why they're bullshit, and try to convince people to stop using them.

Argument 1

We can tell human CO2 changes the climate because since the industrial revolution global temperatures have increased. 
If you cant spot how obviously stupid this is you need to stop reading now and think, time 5 minutes on a clock and spend that time thinking about this argument. Imagine you were trying to infiltrate a group of AGW deniers and you want to convince them you're one of them. How would you pretend to explain this?

Ok, so obviously this is just a fluke right? The warming trend is not that strong, there have been far more dramatic warmings in the past, there will be again. It's just not reasonable to draw this big a conclusion from such a small and wildly fluctuating set of data as average temperatures over the last hundred years or so. Forget the urban heat island and all kinds of other effects to deny this warming is happening. There's no reason at all to suppose it isn't. It just doesn't prove anything in any kind of strong sense.

If you didn't work out that explanation of this argument you wont convince anyone. Unless you can spot holes your arguments at least as well as my 15 year old self you're never going to convince anyone intelligent.

Argument 2

The atmosphere is like a greenhouse. Light from the sun can enter but light reflected off the soil bounces off the CO2 in the atmosphere and is trapped. 
This is not how a greenhouse works. If you open a small vent in the top of a greenhouse you cool it dramatically without really altering what happens to the light in the greenhouse. The way a greenhouse actually works is by stopping the hot air inside escaping to the cooler outside. Obviously the whole atmosphere cant work like this.

If you think about it for a short amount of time (but not too long or you might work out the right answer) you'll easily be convinced that the band of CO2 is symmetric. Just as much as it keeps light reflected from the earth in it must keep light from the sun out. More so in fact, as there's less light coming from the earth (some of it has been absorbed by plants etc).

You can actually make this argument work, but you need to actually sit down and think. One error is using "light" in two different ways. The earth is not a mirror, it does not reflect sunlight back into space unchanged. It reflects much of it as infra-red rather than visible light. CO2 treats IR and visible light differently. You can explain this to young me, and he will understand and agree with you. But nobody did. Everyone assumed that I was (and AGW deniers are) stupid enough to accept this argument as it is. This is foolish.

Argument 3

Look at my sodding great graph. You notice how perfectly CO2 and temperature are correlated? Thus CO2 causes temperature change.

This is the argument that still causes my lingering doubts about AGW (and I still have some). It's astonishing to me that so many people who aren't obviously insane seriously try to use this argument. Again, stop reading, set a timer for 5 minutes. Dont stop thinking until you've either understood why this does not prove the conclusion or the 5 minutes have finished.

Consider this argument:
 Look at my sodding great graph. You notice how perfectly CO2 and temperature are correlated? Thus temperature change causes CO2. 

On the one hand there's a weak prior belief that it ought to be temperature causing the CO2. There are obviously myriad factors affecting temperature: albedo, orbital perturbations, sunspots, cosmic wind, dust in the atmosphere, etc etc. To say that one thing, CO2, is correlated this well with the result of such a wide array of things seems to require one of two things. Either CO2 causes temperature change, and is stupidly powerful in so doing, to render all the other causes moot. Or the temperature drives the CO2. The former is (to someone ignorant of climate science) the less plausible assumption.

Consider now the mechanisms. Unless you've already been given a fixed version of argument 2 there's no obvious mechanism that would suggest to you the flooding the Earth with CO2 would warm it. The other way round this isn't true however. You've got 5 minutes, if I heat the whole Earth up explain why I should expect to see more CO2 in the atmosphere?

There are loads of mechanisms. More forest fires is only the most obvious. Remember also that a huge amount of CO2 can be dissolved in liquids (like coke, or for instance the sea). Remember that the amount that can be dissolved in it varies inversely with the temperature. Coke left out on a hot day goes flat, seas left out on a hot day dump their CO2 into the atmosphere. Add fossil fuels frozen in permafrost and a dozen other easy to think of factors into the mix and it's pretty obvious that we should have a reasonably strong prior belief that temperature causes CO2 changes.

This argument causes me problems. Because to argue with this alone suggest either that you are deliberately trying to deceive me or that you're woefully bad at drawing causal arrows the right way round. Either way I'm not going to trust your climate science. And not unreasonably.

None of these arguments as presented, or indeed many others that I have discovered in the popular literature on the subject, goes any way at all towards convincing a reasonably sane person that AGW exists. The fixed argument from greenhouse gasses is good, but you need to think about it carefully. I didn't see a clear explanation on those lines than convinced me until a couple of years ago at best.

What do I now accept and why?

As always, beliefs aren't simple binary yes/no things. I have different levels of certainty, (that I wouldn't want to try to put numbers on with any large sums of money involved), about several propositions.
If human CO2 output increases at something like the present rate for the next century mean global temperatures averaged over 30 years will at that point be higher than now.
I would be fairly certain of. It seems to me very likely.
If human CO2 output stabilises at current levels then next century mean global temperatures averaged over 30 years will at that point be higher than now.
I would be less certain of, but still highly confident.
If human CO2 output follows SRES scenario A1FI then the resultant warming will be in the range of 2.4 to 6.4 °C
I would call more likely than unlikely, but would be far from certain of.

Why? Because I've read at least the executive summary of the IPCC Fourth Assessment Report and skimmed bits of the rest of it (life is far far too short). Because I've been listening carefully to the assessment of scientists, not of their own opinion, but of the quality of the research done by others. Because I've looked climate change up on google scholar and seen just how many papers this field has produced.

Note what I've not done. I've not read lists of prominent scientists who "believe in AGW". That does not provide strong evidence that AGW is a real phenomenon. I've not read media reports about the recent warming trend, not one of them presents or even considers the statistical significance of the results.

Life is too short for me to become a climate scientist or to assess in detail the validity of any of the detailed methodologies of the IPCC and others. This does not and absolutely must not mean that I ought to accept lists of names of scientists as evidence. If they've not read the research either (and almost all of them haven't, their lives are also short) then their view is just as ill-informed as mine.

What matters is the people who have read this stuff, who do understand in detail the statistical significance of these models. What matters is that the papers are peer-reviewed, that bad methodologies are attacked publicly. When flat errors like the Himalayan Glacier fiasco are found they are quickly corrected. What matters is that this stuff is real science.

And unless you've got evidence-based confidence in the scientific method, unless you can be reasonably confident in its conclusions without being able to follow the details, you cant say that. And then guess what, unless some decent public science education has happened you'll end up not believing in AGW. It's not surprising, nor is it a moral wrong on the part of the public.

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