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Table 1

Characteristics and Assumptions of Various Scenarios

Scenario

A1FI

A2

B2

B1

Population in 2085 (billions)

7.9

14.2

10.2

7.9

GDP growth factor, 1990­2100

525­550

243

235

328

GDP/capita in 2085, Global average

$52,600

$13,000

$20,000

$36,600

GDP/capita in 2100

Industrialized countries

$107,300

$46,200

$54,400

$72,800

Developing countries

$66,500

$11,000

$18,000

$40,200

Technological change

Rapid

Slow

Medium

Medium

Energy use

Very high

High

Medium

Low

Energy technologies

fossil

regionally

"dynamics

high

intensive

diverse

as usual"

efficiency

Land use change

Low­medium

Medium­high

Medium

High

CO2 concentration in 2085

810

709

561

527

Global temp change (°C) in 2085

4.0

3.3

2.4

2.1

Sea level rise (cm)

34

28

25

22

Sources: N. W. Arnell, "Climate Change and Global Water Resources: SRES Emissions and Socio-Economic Scenarios,"

Global Environmental Change 14, no. 1 (2004): Tables 1, 6, 7; and R. J. Nicholls, "Coastal Flooding and Wetland Loss

in the 21st Century: Changes under the SRES Climate and Socio-Economic Scenarios," Global Environmental Change

14, no. 1 (2004): Tables 2 and 3. GDP and GDP/capita are in 1990 U.S. dollars. Note: Global temperature change is based

on the HadCM3 model.

preferred to predictions because predictions of

estimate whether unmitigated climate change

the above mentioned socioeconomic trends

will lower future well-being to below today's

that determine emissions over the course of the

levels. Specifically, I will assume for the sake

next 100 years are extremely unreliable.

of argument that climate change under the

The FTA report employed emission sce-

warmest scenarios will result in a welfare loss

narios developed by the IPCC's Special Report

equivalent to 35.2 percent of GDP in 2100.

on Emissions Scenarios to project future climate

change from 1990 (the base year for each sce-

IPCC Scenarios of the Future

nario) through 2100.13 The emissions scenar-

In 2000, the IPCC developed four "families"

of greenhouse emissions scenarios to depict

ios assume that no new policies or measures

what the future might look like given different

will be implemented to reduce damages from

assumptions about demographic, technologi-

climate change. This assumption virtually

cal, economic, and social trends during the

guarantees that negative impacts will be over-

period 1990­2100. This study is primarily con-

estimated, while positive impacts will be

cerned with exploring, in light of the results of

underestimated.

the FTA and Stern Review, the implications for

The dominant characteristics of the "story-

The IPCC

human well-being and environmental quality

lines" used in those scenarios are shown in

in four scenarios, with each scenario represent-

Table 1. Table 1 also provides corresponding

scenarios repre-

ing one family.

estimates for the atmospheric CO2 concentra-

sent plausible

The IPCC scenarios are less predictions

tions, temperature increases, and sea level rise

that result from each scenario through 2085.14

futures that serve

than they are inputs for "if-then" calculations.

That is, the scenarios (sometimes called "story-

Those impact calculations are the product of

as grist for the

lines") represent plausible futures that serve as

chained computer simulations discussed in

analytic mill.

grist for the analytic mill. Scenarios are often

the FTA subsection above.

4