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leads to higher estimates of the population at

This is evidenced, for example, in the remark-

risk in the A1FI scenario relative to the B1

able declines--99 percent or greater--during the

scenario.

20th century in mortality and morbidity rates

Second, neither the FTA studies nor the

in the United States for various water-related

Stern Review deal very satisfactorily with

diseases, e.g., typhoid, paratyphoid, dysentery,

malaria and various gastrointestinal diseases.26

endogenous adaptation. Some FTA studies

(e.g., the ones for hunger and coastal flood-

This study highlights the tension between

ing) allow for some "spontaneous" adaptive

the public health and environmental improve-

responses because it should be expected that

ments associated with wealth creation and

even in the absence of new governmental

technological advance on one hand and the

policies, people would employ existing tech-

countervailing negative impacts on the same

nologies to protect themselves from econom-

from increased greenhouse gas emissions on

ic or bodily harm even in a "business-as-

the other hand. By and large, as I will show, the

usual" world. Yet the study for water stress

FTA and Stern Review confirm that richer and

doesn't allow for any adaptation. And even

warmer worlds will not necessarily have lower

where the FTA studies allow for some adap-

levels of human and environmental well-being

tation, they limit the range of available tech-

than poorer but cooler worlds.

The FTA and

nological options to currently available tech-

Stern Review

nologies.28 But we should expect that the

The Impact of Climate

menu of technological options would be

confirm that

Change­Four Scenarios

much broader, more cost-effective, and more

richer and

affordable in the future under any scenario

warmer worlds

because of the following:

In this section I present the FTA's scenario

estimates of the populations at risk in 2085

will not necessari-

· The world will be wealthier under any of

with and without climate change for four cli-

ly have lower

mate-sensitive threats to human well-being--

the scenarios (see Table 1) and, there-

hunger, water stress, coastal flooding, and

fore, better able to develop, afford, and

levels of human

malaria--and on a number of environmental

implement new as well as improved

and environmen-

indicators that are also sensitive to climate.

technologies;

tal well-being

·

When comparing the population at risk

Technology will, through the accretion

from these threats without climate change

of knowledge, advance, even if society

than poorer but

with the population at risk from these threats

doesn't get any wealthier; and

cooler worlds.

·

with climate change, a couple of issues should

Even in the absence of specific policy

be kept in mind.

changes, new and improved technologies

First, the A1FI and B1 scenarios are

will inevitably be developed to specifical-

assumed by the IPCC to have the same popu-

ly cope with the negative impacts of cli-

lation in 2085. That assumption, however, is

mate change.

dubious. In the real world, lower total fertili-

ty rates are generally associated with higher

Hence, limiting adaptation between now

levels of economic development.27 Hence, the

and 2085 to "current" technologies is tanta-

mount to estimating today's food produc-

A1FI world should have a lower population

tion based on the technology of 1920 (or ear-

in 2085 than the B1 world. Accordingly, the

lier). Any such estimate is bound to underes-

populations at risk in the A1FI scenario are

timate food production and overestimate

probably overestimated relative to the B1 sce-

hunger.29 In our case, doing so overestimates

nario. Likewise, relative to the B1 scenario,

greenhouse gas emissions and associated cli-

the population at risk in all scenarios, but the

mate changes are probably overestimated in

overestimates are greatest for the A1FI sce-

the A1FI scenario because emissions would

nario, followed by B1, B2 and A2, in that

be lower in a less-populated world. That, too,

order.

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