Matheny, 7—[Jason, Department of Health Policy and Management, Bloomberg School of Public Health, Johns Hopkins University. “Reducing the Risk of Human Extinction.” Risk Analysis. Vol 27, No 5, 2007, http://www.upmc-biosecurity.org/website/resources/publications/2007_orig-articles/2007-10-15-reducingrisk.html]
5. Discounting An extinction event today could cause the loss of thousands of generations. This matters to the extent we value future lives. Society places some value on future lives when it accepts the costs of long-term environmental policies or hazardous waste storage. Individuals place some value on future lives when they adopt measures, such as screening for genetic diseases, to ensure the health of children who do not yet exist. Disagreement, then, does not center on whether future lives matter, but on how much they matter.6 Valuing future lives less than current ones (“intergenerational discounting”) has been justified by arguments about time preference, growth in consumption, uncertainty about future existence, and opportunity costs. I will argue that none of these justifications applies to the benefits of delaying human extinction. Under time preference, a good enjoyed in the future is worth less, intrinsically, than a good enjoyed now. The typical justification for time preference is descriptive—most people make decisions that suggest that they value current goods more than future ones. However, it may be that people’s time preference applies only to instrumental goods, like money, whose value predictably decreases in time. In fact, it would be difficult to design an experiment in which time preference for an intrinsic good (like happiness), rather than an instrumental good (like money), is separated from the other forms of discounting discussed below. But even supposing individuals exhibit time preference within their own lives, it is not clear how this would ethically justify discounting across different lives and generations (Frederick, 2006; Schelling, 2000). In practice, discounting the value of future lives would lead to results few of us would accept as being ethical. For instance, if we discounted lives at a 5% annual rate, a life today would have greater intrinsic value than a billion lives 400 years hence (Cowen & Parfit, 1992). Broome (1994) suggests most economists and philosophers recognize that this preference for ourselves over our descendents is unjustifiable and agree that ethical impartiality requires setting the intergenerational discount rate to zero. After all, if we reject spatial discounting and assign equal value to contemporary human lives, whatever their physical distance from us, we have similar reasons to reject temporal discounting, and assign equal value to human lives, whatever their temporal distance from us. I Parfit (1984), Cowen (1992), and Blackorby et al. (1995) have similarly argued that time preference across generations is not ethically defensible.7 There could still be other reasons to discount future generations. A common justification for discounting economic goods is that their abundance generally increases with time. Because there is diminishing marginal utility from consumption, future generations may gain less satisfaction from a dollar than we will (Schelling, 2000). This principle makes sense for intergenerational transfers of most economic goods but not for intergenerational transfers of existence. There is no diminishing marginal utility from having ever existed. There is no reason to believe existence matters less to a person 1,000 years hence than it does to a person 10 years hence.Discounting could be justified by our uncertainty about future generations’ existence. If we knew for certain that we would all die in 10 years, it would not make sense for us to spend money on asteroid defense. It would make more sense to live it up, until we become extinct. A discount scheme would be justified that devalued (to zero) anything beyond 10 years. Dasgupta and Heal (1979, pp. 261–262) defend discounting on these grounds—we are uncertain about humanity’s long-term survival, so planning too far ahead is imprudent.8 Discounting is an approximate way to account for our uncertainty about survival (Ponthiere, 2003). But it is unnecessary—an analysis of extinction risk should equate the value of averting extinction at any given time with the expected value of humanity’s future from that moment forward, which includes the probabilities of extinction in all subsequent periods (Ng, 2005). If we discounted the expected value of humanity’s future, we would count future extinction risks twice—once in the discount rate and once in the undiscounted expected value—and underestimate the value of reducing current risks. In any case, Dasgupta and Heal’s argument does not justify traditional discounting at a constant rate, as the probability of human extinction is unlikely to be uniform in time.9 Because of nuclear and biological weapons, the probability of human extinction could be higher today than it was a century ago; and if humanity colonizes other planets, the probability of human extinction could be lower then than it is today. Even Rees’s (2003) pessimistic 50-50 odds on human extinction by 2100 would be equivalent to an annual discount rate under 1% for this century. (If we are 100% certain of a good’s existence in 2007 but only 50% certain of a good’s existence in 2100, then the expected value of the good decreases by 50% over 94 years, which corresponds to an annual discount rate of 0.75%.) As Ng (1989) has pointed out, a constant annual discount rate of 1% implies that we are more than 99.99% certain of not surviving the next 1,000 years. Such pessimism seems unwarranted. A last argument for intergenerational discounting is from opportunity costs: without discounting, we would always invest our money rather than spend it now on important projects (Broome, 1994). For instance, if we invest our money now in a stock market with an average 5% real annual return, in a century we will have 130 times more money to spend on extinction countermeasures (assuming we survive the century). This reasoning could be extended indefinitely (as long as we survive). This could be an argument for investing in stocks rather than extinction countermeasures if: the rate of return on capital is exogenous to the rate of social savings, the average rate of return on capital is higher than the rate of technological change in extinction countermeasures, and the marginal cost effectiveness of extinction countermeasures does not decrease at a rate equal to or greater than the return on capital. First, the assumption of exogeneity can be rejected. Funding extinction countermeasures would require spending large sums; if, instead, we invested those sums in the stock market, they would affect the average market rate of return (Cowen & Parfit, 1992). Second, some spending on countermeasures, such as research on biodefense, has its own rate of return, since learning tends to accelerate as a knowledge base expands. This rate could be higher than the average rate of return on capital. Third, if the probability of human extinction significantly decreases after space colonization, there may be a small window of reducible risk: the period of maximum marginal cost effectiveness may be limited to the next few centuries. Discounting would be a crude way of accounting for opportunity costs, as cost effectiveness is probably not constant. A more precise approach would identify the optimal invest-and-spend path based on estimates of current and future extinction risks, the cost effectiveness of countermeasures, and market returns. In summary, there are good reasons not to discount the benefits of extinction countermeasures. Time preference is not justifiable in intergenerational problems, there is no diminishing marginal utility from having ever existed, and uncertainties about human existence should be represented by expected values. I thus assume that the value of future lives cannot be discounted. Since this position is controversial, I later show how acceptance of discounting would affect our conclusions.