There is a huge fallacy of the excluded middle in the AGW debate.
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Proponents say that global warming is happening, and humans are contributing to it, and therefore we need to take immediate action.
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Opponents tend to focus on ‘debunking’ the entire concept of human-caused global warming.
I personally believe that the science is fairly well established that humans are contributing to the warming of the planet. It’s time the debate shifted from that basic fact and focuses more on what can and should be done about it.
In my opinion, once you get away from the basic mechanisms of warming and start casting models out 100 years in the future, you are on very, very thin ice scientifically. We simply don’t know enough about all the mechanisms that contribute to long-term climate trends. We don’t fully understand the contributions of various planetary and extra-planetary forces. The earth’s climate is a highly complex system - perhaps too complex for us to model and understand.
As an analogy, consider our understanding of how markets work. We understand markets well enough to be able to predict certain things - for example, that if all else is equal and you raise interest rates, economic growth will slow down. Or if you pump more money into the economy, all else being equal prices will rise. We actually know this stuff with a high degree of precision. We understand all the contributors to the effects in question. We have mathematical models which explain these forces.
Now try to take that information and build a model which predicts where the Dow Jones average will be in ten years. Good luck with that.
The problem is that even if the basic mechanisms are known, in the real world there are so many variables and so many feedback loops and unforeseen events that the system is just too complex to model.
Getting back to climate: Ten years ago, not a single one of the atmospheric models that predicted global temperatures 50 years from now predicted that temperatures would stay flat from 2001 until now - but they did (although there was significant variation from year to year, the overall trend is flat through those years). New contributions to the field are quite recent - new data on the contribution of cosmic rays, new information about water vapor effects, etc. We’re still learning.
Next, there is an important question regarding what can be and should be done about it. Let’s assume our models are pretty accurate. What do they tell us about potential damage? When will that damage occur, how much will it cost us, and what is the net present value of that future damage? After all, a 1 trillion dollar expense to be paid 100 years from now actually has a relatively small net present value, and you’d be crazy to spend even a tenth of that amount to avert the 1 trillion cost later on.
The ‘act now’ side of the debate seems to assume that any amount of man-made global warming is too much, but the IPCC itself has said that warming on the order of 2.5 degrees C or less would actually result in an overall economic benefit for the planet (i.e. the gains in the temperate regions would more than make up for the losses in the equatorial and coastal regions). If that’s the case, then economically speaking why would you even want to do something about it? So the question of the amount of warming is critically important to determining current policy, as is a good understanding of the limitations of the models and the error bars around the numbers so we can price the risk of greater damage accordingly.
Note that I’m talking about purely economic costs. We can talk about costs in terms of changes to ecosystems and such, but that’s an overtly political discussion. We need to stay grounded in hard numbers here, so discussing the issue in terms of the economic cost of dislocations and property destruction and energy costs and such seems more fruitful.
Even if we assume that there is a significant net present cost of future warming, it is not at all clear that the correct approach is to attempt to curb carbon emissions. For example, let’s say we could determine that the net present cost of future warming is 100 billion dollars. One response to that could be to simply start a UN ‘global warming mitigation fund’, with various wealthy nations contributing to it to the tune of 100 billion dollars per year. Then use that money over the years to pay reparations to the countries damaged.
As it turns out, the median model for warming damage by the IPCC suggests that global warming will probably help the economies of the rich nations in the high latitudes (by lowering heating costs and increasing growing seasons, for example), but impose severe costs on the poorer nations which tend to be closer to the equator. So one way to mitigate this is to simply set up a program of wealth transfer from the rich countries to the poor countries to compensate them.
The final question to be asked is, “Even if warming is happening and is man-made, and even if the math tells us that the best way to respond is to cut carbon emissions, is it even possible to do that?”
There are plenty of reasons to suggest that it’s simply not politically possible to cut carbon emissions by any serious amount - too many countries have their economies bound to carbon, and the reality of the fungible oil market is that voluntary, unilateral reductions in oil consumption by one country simply cause the price to decline, which stimulates consumption elsewhere. There’s also the problem that alternative sources of energy are still too expensive, too unreliable, and not ready to take the place of, say coal.
So get away from the trap of trying to argue for or against the existence of man-made warming itself. It’s actually the easiest question to answer (yes), but the least important in terms of determine what to actually do next. After all, even if warming was occurring naturally, we’d still be left with the other questions about how to figure out the cost, and what to do about it.