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generate emissions scenarios; and

be projected semi-realistically for more than

·

5­10 years at a time."5

the creation of new or improved tech-

nologies that would come on line over

Emission scenarios are used to drive models

time, because technology accrues over

to estimate future trends in atmospheric

time.6

greenhouse gas concentrations. Those concen-

trations are then used to model the amount of

heating (or "radiative forcing" ) of the climate

In other words, the impact assessments

system which is next fed into coupled atmos-

are inconsistent with the assumptions built

phere-ocean general circulation models to esti-

into the emissions scenarios used to drive cli-

mate spatial and temporal changes in climatic

mate change.

variables, which are in turn used as inputs to

Despite these shortcomings, for the pur-

simplified and often inadequate biophysical

poses of this study I will, for the most part,

models that project location-specific biophysi-

take the results of the FTA at face value

cal changes pertaining to the resources that are

because it has figured prominently in the

affected by climate change (e.g., vegetation and

international debate on global warming and

other species, crop, or timber yields).

because it allows us to develop estimates of

The finer the spatial scale of the analysis,

the relative contribution of climate change to

The results

the greater the uncertainties in climatic vari-

various climate-sensitive problems in the

of impact assess-

future.7 Like the FTA, this paper does not

ables. But because the resources that are affect-

ed by climate change are spatially heteroge-

consider low-probability but potentially

ments are subject

neous--as are the socioeconomic conditions

high-consequence outcomes such as a shut-

to potentially

that affect those resources and determine

down of the thermohaline circulation or the

large systematic

whether and how human beings will respond

melting of the Greenland and Antarctic ice

to changes--it is more appropriate to do the

sheets. They are deemed unlikely to occur

errors which tend

during this century if they occur at all.8

biophysical impacts analysis at the local scale

to substantially

than at larger regional or national scales.

Finally, depending on the human or nat-

Stern Review

overstate negative

ural system under consideration, the outputs

The Stern Review on the Economics of Climate

impacts.

of these biophysical models may have to be

Change was commissioned from Nicholas

fed into additional models to calculate the

Stern, the erstwhile chief economist of the

social, economic, and environmental impacts

World Bank, by the then-chancellor of the

on those systems, including the calculation

exchequer, Gordon Brown, on behalf of the

of regional and global scale impacts through

British government. It was released on October

the use of trade models.

30, 2006. The Stern Review estimated that

In addition to the cascading uncertainties

unmitigated climate change will reduce welfare

that propagate from model to model--the

by an amount equivalent to a reduction in con-

cumulative effects of which have yet to be

sumption per capita of 5­20 percent "now and

quantified--the results of these impact

forever" if one accounts for market and non-

market impacts and the risk of catastrophe.9 It

assessments are subject to potentially large

systematic errors which tend to substantially

also suggested that by the year 2200, the 95th

overstate negative impacts while simultane-

percentile of the equivalent per capita GDP

losses could rise to 35.2 percent.10

ously understating positive impacts of cli-

mate change. Those systematic errors are due

Several researchers have disputed the Stern

to the fact that the assessments generally do

Review's impact estimates and consider them

greatly overblown.11 The review's authors

not account fully, if at all, for the increases in

adaptive capacity resulting from

themselves emphasize "strongly" that the

numbers should not "be taken too literally."12

· increases in wealth postulated under the

I will, nevertheless, put aside these concerns

socioeconomic assumptions used to

and accept the Review's findings in order to

3