Emissions Scenarios - IPCC

Scenario Driving Forces 107
Section 3.4 examines energy resources and tecimology in more
detail, and Section 3.5 addresses agriculture, forestry, and landuse
change. Section 3.6 considers other sources of ПОП-СО2
GHÍGs. The chapter concludes with a discussion of non-climate
policies and their potential impact on the principal driving
forces of future emissions. Each section briefly reviews past
trends, available scenarios, and important new methodological
and empirical advances since the publication of previous
International Panel on Climate Change (IPCC) emissions
scenarios in 1992 (IS92). This chapter provides the background
to establish recommendations for the range of driving-force
variables to be explored in the new set of scenarios. The
available literature and current understanding of the inherent
uncertainties in developing very long-term scenarios are
reflected. Each section elucidates in detail the important
relationships between scenario driving forces, as the question
of relationships is a new and important mandate for SRES.
Nonetheless, most attention is paid to the possible relationships
between population and economic growth, because this is the
area most intensively discussed in the literature.
3.2. Population
3.2.1. Introduction
Population projections are arguably the backbone of GHG
emissions scenarios, and are comparable in some ways with
them. Population projections cover timeframes of a century or
more, and they involve social and economic considerations and
uncertainties similar to those in GHG emissions scenarios.
Population projections are among the most commonly cited
indicators of the future state of the world. Compared to the
multitude of projection efforts they have a relatively high
accuracy in the near-to-medium term. Even so the future is
always unknowable and surprises are in store, as confirmed by
a cursory review of the past history of population projections in
which fundamental events were largely unforeseen (post-
World War II baby boom, acquired immunodeficiency
syndrome (AIDS) or the recent rapidity of fertility decline in
developing countries)).
To be useful for the development of emissions scenarios,
population projections need a timeframe of a century or more.
global coverage and regional disaggregations, and an
appropriate treatment of uncertainty reflected in the variants of
the projections. Although other "demographic units" more
immediately linked to GHG emissions than people, such as
automobiles or households, can be considered, the integrated
assessment models used in this report are all based on regional
population and, in some cases, labor-force projections.
3.2.2. Past Population Trends
World annual population growth rates probably averaged less
than 0.6% during the 18* and 19"^ centuries, passed the 1% rate
around 1920, and peaked at 2.04% in the late 1960s (UN,
1998). This peak coincided with growing international concern
about population growth in general. World population reached
1 billion in 1804, 2 billion in 1927, 3 billion in I960, 4 billion
in 1974, and 5 billion in 1987, reaching the 6 bilhon level
shortly before the millenium (UN, 1998).
The population of the developing regions increased from 1.71
bilUon in 1950 to 4.59 billion in 1996, with annual growth rates
dropping from a peak of 2.5% in 1965 to 1.7% presently. The
population of the more-developed regions increased from 813
million to 1.18 billion over the same period, with annual
growth rates dropping from 1.2% in 1950 to 0.4% presenfly
(UN, 1998). Population distribution and growth thus differ
markedly among major geographic regions. Latin America and
the Caribbean was the fastest growing region between 1950
and 1970, followed by Africa, and this is projected to remain
the case until 2050 (UN, 1998). Table 3-1 shows the population
levels of the major geographic areas between 1800 and the
present.
3.2.3. Population Scenarios
3.2.3.1. Population Projections Used in Emission Sceitarios
Since the IPCC was first convened in 1988, its Working Group
III has generated two distinct series of emissions scenarios; the
1990 Scientific Assessment (SA90) series of four scenarios
(Houghton et al., 1990), and the IS92 series of six scenarios
(Houghton et al., 1992, 1995; Pepper et ai, 1992). The four
Table 3-1: Population of the world and by major areas between 1800 and 1996 in millioits. Data source: UN, 1998.
1800 1850 1900 1950 1996
World 978 1262 1650 2524 5768
Africa 107 111 133 224 739
Asia 635 809 947 1402 3488
Europe 203 276 408 547 729
Latin America and Caribbean 24 38 74 166 484
Northern America 7 26 82 172 299
Oceania 2 2 6 13 29