What Al Gore doesn't understand about climate change.

How the dismal science applies to your life.
Oct. 22 2007 7:44 AM

Save the Earth in Six Hard Questions

What Al Gore doesn't understand about climate change.

Illustration by Robert Neubecker. Click image to expand.

Barring a last-minute intervention by the Supreme Court, the 2007 Nobel Peace Prize will be shared by Albert Gore Jr. Admittedly, Gore has been less of a menace to world peace than some previous laureates (think Henry Kissinger). But there is nothing particularly peaceable about Gore's rhetorical approach to climate policy. At his most pugnacious, Gore has depicted the fundamental trade-off as one between environmental responsibility and personal greed. Of course, as everyone over the age of 12 is perfectly aware, the real trade-off is between the quality of our own lives and the quality of our descendants'.

In other words, climate policy is almost entirely about you and me making sacrifices for the benefit of future generations. To contribute usefully to the debate, you've got to think hard about the appropriate level of sacrifice. That in turn requires you to think hard about roughly half a dozen underlying issues.

1. How much does human activity affect the climate? This is actually a whole menu of questions: What can we expect given the current level of carbon emissions? What if we cut those emissions by half? By two-thirds? And so on. These are questions for physical scientists, not economists or politicians.

2. How much harm (or good!) is likely to come from that climate change? This is partly a matter of physical science and partly a matter of economics. If the world temperature rises 3 degrees, agronomists try to predict the wheat yield in Oklahoma; economists try to predict when Oklahomans will turn to alternate ventures—and when it will become profitable to grow wheat in Alaska. Climatologists estimate what it takes to put New York underwater; economists estimate the cost of moving New York inland.

3. How much do we—or should we—care about future generations? Edmund Phelps, the 2006 Nobel laureate for economics, argued long ago that you (and I) should care exactly as much about a stranger born 1,000 years hence as we do about a stranger who's alive today. Phelps' view has been highly influential among economists, who now take it as more or less the default position. But even economists are sometimes wrong, and there are powerful arguments for "discounting" the welfare of future generations. First, many people (myself excluded, however) believe we should care more about our countrymen than about a bunch of foreigners—hence the sentiment for a border fence. If we are allowed to care less about people who happen to be born in the wrong country, why can't we care less about people who happen to be born in the wrong century? And second: Few of us feel morally bound to churn out as many children as we possibly can, which means we think nothing of denying future generations the gift of life. If it's OK to deny them their very lives, shouldn't it be OK to deny them a temperate climate?

There is a ton more to be said in response and counter-response, but in the end, you've got to take a stand. Does the next generation count 100 percent as much as our own, as Edmund Phelps demands? Or 99 percent? 95 percent? 90 percent? I'll show you later how much the answer matters.

4. How likely are those future generations to be around, anyway? If you think life on Earth will be destroyed by an asteroid in 200 years, it makes little sense to worry about the climate 300 years from now. (Of course, the issue is complicated by the fact that our climate policies change the survival odds.)

5. Just how rich are those future generations likely to be? If you expect economic growth to continue at the average annual rate of 2.3 percent, to which we've grown accustomed, then in 400 years, the average American will have an income of more than $1 million per day—and that's in the equivalent of today's dollars (i.e., after correcting for inflation). Does it really make sense for you and me to sacrifice for the benefit of those future gazillionaires?

6. How risk-averse are we? This matters not just because of uncertainty about the effects of climate change but because it affects the way future generations want us to behave. Imagine yourself as a disembodied soul, waiting in line to be born—possibly next year, possibly 100 years hence. If you have little tolerance for risk, you'll want us to pursue policies that make life about equally good at all times; if you're willing to roll the dice, you might prefer a policy that allows some generations to live riotously at the expense of others.

Only after you've addressed each question in turn can you say something sensible about climate policy. To carry out that program in detail would indeed be a Nobel-worthy achievement. I don't propose to earn my Nobel Prize in this column space, but I can at least offer a quick back-of-the-envelope calculation to show you how this stuff works.

First, I'll make the extreme assumption that our environmental recklessness threatens to shave 1 percentage point off economic growth forever. Because of compounding, our disposable incomes will be reduced by 9.5 percent a decade from now and by 63 percent a century from now—perhaps because we'll spend 63 percent of our incomes relocating coastal cities. Now toss in some standard (but arguable) assumptions about risk aversion and discounting. (Note to econogeeks: I assumed a risk-aversion coefficient of 1, and I discounted future generations' welfare at an annual rate of 5 percent, partly because we might care less about them and partly because we're not sure they'll exist.) Run this through your calculator, and you'll find we should spend up to about 17 percent of our incomes on climate control—provided that our investment is effective. That's an expenditure level that I expect would satisfy Al Gore.

Change the numerical assumptions, and you'll change the numerical conclusion. Make the discount rate 1 percent instead of 5 percent, and you can justify spending up to a whopping 62 percent of our incomes on climate control; lower the discount rate to 10 percent, and you can't justify spending more than 8 percent of our incomes.

The moral of that story is not that economists can justify anything; it's that assumptions really matter. Therefore you need to be clear about your assumptions, and you need to be prepared to justify them. If you're not talking about discount rates and levels of risk aversion, you're blathering.

The most thoughtful assessment of climate change is the Stern Review, prepared in October 2006 at the behest of the British government. The Stern Review reaches conclusions generally compatible with Al Gore's worldview, but only after laying out the underlying assumptions so clearly that skeptics like me can tinker around with them and see how the conclusions change. In other words, they've taken a hot-button issue and reduced it to its constituent pieces so that opposing parties can stop yelling at each other and say, "Let us calculate." That's what I call a contribution to world peace. I wish the Nobel Committee had agreed.

Steven E. Landsburg is the author, most recently, ofMore Sex Is Safer Sex: The Unconventional Wisdom of Economics. You can e-mail him at armchair@landsburg.com.