So naturally, it's time for a global warming post. And NYT journalist Andy Revkin's provided a good starting point, dropping an illuminating bit of insight in a post Tuesday evening:
But after reviewing the chapter myself just now, I have to say that at least one passage — as far as I can tell — did not contain a single caveat and did not reflect the underlying body of evidence and analysis at the time (or even now):
Human-induced warming of the climate system is widespread. Anthropogenic warming of the climate system can be detected in temperature observations taken at the surface, in the troposphere and in the oceans.I have yet to see anyone provide definitive evidence — with no error bars — that the fingerprint of human-generated greenhouse gases (or other emissions or actions) is unequivocal. The only thing described as “unequivocal” in the report was the warming, not the cause, unless I really haven’t been paying attention for the last two decades.
The language around "no error bars" is what I wanted to call out here, because it reflects a widely held belief that there's a bright line between certain and uncertain - and more importantly, that it's prudent to wait until we're "certain" about something before taking any action. Indeed, it's this notion - that there's such a thing as "certainty" in science - which enables deniers and delayers to get away with spouting alarmist nonsense like, "the science is not settled!" and "we shouldn't risk trillions of dollars in GDP until we know for certain humans are causing global warming!"
The problem is, as any true skeptic knows, there's no such thing as certainty in science - at least to the degree that a scientific study could ever hope to show "no error bars." Remember, even something as obvious as gravity still has scientific uncertainty associated with it; Einstein proved that gravity's nature was different than how Isaac Newton imagined it, and even Einstein's theories are not reconciled with Quantum Mechanics.
This is especially true for climate science, which is intimately concerned with predicting the future. The earth is not a controlled experiment that allows scientists to add CO2 and empirically test the precise amount of warming that results. There are simply too many variables not in scientists' control. To predict the consequences of carbon emissions, we must therefore rely on climate models built from our best understanding of how the climate system works. And yes, those models are uncertain, with error bars greater than zero: as with any prediction of future events, you inherently can never be certain you're right until those events have already occurred. Certainty can only exist with hindsight.
But here's the kicker: once we're in a position to make hindsight judgments on CO2, once we've reached the point that we can empirically assess CO2's impact on climate in the real world, it will be too late to avert the effects. This is because once CO2 gets into the atmosphere, it takes several decades for the temperature to catch up with the new energy imbalance (see here, here, and here for explanations). So even if you stopped all CO2 emissions today, there would still be warming left "in the pipeline." Moreover, it's likely that once warming crosses a certain threshold, certain feedbacks will take over that drive continued warming regardless of what happens with CO2. Choices we make today commit us to consequences tomorrow.
Thus, as in any facet of life, we must make decisions today in a world of uncertainty, based on our best predictions of what will happen tomorrow; past a certain point, debating levels of certainty is a fruitless recipe for dithering and delay. A businessman who waits for certainty that an investment will pay off will lose the opportunity to a bolder entrepreneur.
Similarly, by the time we've received empirical confirmation of how much humans are contributing to global warming, it will be too late to do anything about it. We can't be certain whether a doubling of CO2 will ultimately result in 1.1 degrees C or 6.4 degrees C of warming, but we can make a pretty good guess, and the latter end of that spectrum would result in a nightmarish world out of "science fiction." It seems prudent, therefore, to invest a small amount of GDP as insurance against the risk of catastrophe. (Indeed, as The Economist points out in making this argument, the investment required to curb global warming is less than the world spends on insurance every year). 73% of economists and the world's biggest re-insurance company agree with me.
The bottom line: Just because we are not certain whether or not bad events will happen in the future does not mean we should not take action to hedge against those risks. By definition, if your condition for acting on greenhouse gases is 100% certainty in the science, then we can never act in time to make an impact. If you want to gamble our future by continuing to emit greenhouse gases, the question becomes, do you feel lucky? Well, do ya punk?
Just don't expect the rest of us to play at your climate craps table.
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