Back in June, Al Gore argued in The New Republic for a calm and numerical risk-assessment approach to dealing with environmental issues. Now conservative Jim Manzi has taken up the challenge in the same publication, arguing that the numbers show that addressing global warming now would cost more than dealing with it when it happens. Manzi also draws in economist Paul Krugman's piece on "building a green economy" from The New York Times Magazine, where Krugman argues that the risk of catastrophe should have a greater effect on cost calculations. Have a look at how it all plays out.

  • Why Uncertainty Means We Should Act Now  "You might think that this uncertainty weakens the case for action, but it actually strengthens it," argues Krugman in the section Manzi highlights. "If there is a significant chance of utter catastrophe, that chance--rather than what is most likely to happen--should dominate cost-benefit calculations. And utter catastrophe does look like a realistic possibility, even if it is not the most likely outcome."
  • Why, According to the Numbers, We Shouldn't  The Intergovernmental Panel on Climate Change's worst-case scenario sees a roughly 4°C warming over the next century, explains Manzi, which would cost about 3 percent of global GDP. By contrast, using less energy, "substitut[ing] higher-cost sources of energy for fossil fuels," and paying for offsets would cost about 6 percent of world GDP. Thus, "the expected economic benefits of emissions mitigation do not cover its realistically expected costs." Manzi acknowledges that some, like Krugman, see things like carbon cuts as, essentially, an "insurance policy" against catastrophe. But that means "the only real argument for rapid, aggressive emissions abatement, then, boils down to the weaker form of the uncertainty argument: that you can't prove a negative." In his view, it then makes more sense to invest in "technology that would provide us with response options in the event that we are currently radically underestimating the impacts of global warming."
  • The Problem With These Numbers  Bradford Plumer, also writing at The New Republic, rebuts Manzi by suggesting he's "clinging way too tightly to the IPCC report," which, though good, is "dated." Plumer also points out that "the worst-case scenarios could be really freaking bad. Like, civilization-destroying bad. And that prospect, even if it's slim, is a great reason to cut emissions." He's not sure Manzi has a good counter-argument here. Finally, he wonders about which is more resilient, the economy or nature:
I've noted before that pretty much every environmental regulation that's ever been enacted has been greeted with predictions of economic doom—yet those dire warnings have never panned out. Pollution restrictions invariably turn out to be much cheaper than expected, in part because they trigger the development of new technologies. (By contrast, nature isn't nearly so forgiving when we try to muck with it.)
  • The Problem With Numbers in General in This Case  "We're a pretty advanced society," writes The Washington Post's Ezra Klein, jumping into the debate, "but we're quite bad at dealing with disasters involving the planet itself." He seems to agree with Plumer that the economy is slightly more predictable:
There's a range of likely outcomes from a tax on carbon, and we can handle most of them. There's also a range of outcomes from radical changes in the planet's climate, and we've really no idea which we can handle, and which we can't. We don't even really know what that range looks like. And although a tax can be undone or reformed, there's no guarantee that we can reverse hundreds of years of rapid greenhouse gas buildup in the atmosphere. If you want proof, look at our inability to deal with an underwater oil spill ...