Present climate and biological change - Climate Change: Biological and Human Aspects - page 224

5

Business-
as-Usual

4

3 Scenario B

Scenario C
Scenario D

2

1

0

1850 1900 1950 2000 2050 2100

Year

Fig. 5.6 GraphsoftheIPCC1990scenarios.Redrawnwithpermission.

not seemingly concerned with the degree of climate change, but what they should
do about managing or controlling change per se. As we shall see in Chapter 8, even
when leading politicians met in December 1997 in Kyoto, Japan, the policy questions
largely boiled down to whether countries would sign up to such a modest international
agreement that (according to the IPCC scientific conclusions) it would not halt the
increase in global warming but might slightly slow down the rate of increase in
warming.
Meanwhile, the IPCC's 1990 B-a-U envelope has not yet (in 2012) been effectively
superseded. Even in each of the IPCC's subsequent reports - 1992, 1995, 2001, and
2007 - the range of scenarios had the 'best estimates' for warming still within the
1990 high - low envelope of the B-a-U scenario. Only the high - low envelopes of
just a few of the special 2001 policy scenarios went outside the IPCC 1990 high -
low B-a-U envelope and that was just at the low end (1.15 ◦ C less warming for 2100
since 1750 than the low B-a-U estimate presented in 1990). So, while Figures 5.6
and 5.7 provide best estimates for various IPCC 1990 scenarios, the 2001 IPCC all-
scenario and all-model envelopes respectively, and the 2007 IPCC selected scenarios,
it is important to note that Figure 5.5, showing the original 1990 B-a-U scenario,
is so similar to the 2001 all-model best-estimates envelope (Figure 5.7a) and the
IPCC 2007 principal scenarios (Figure 5.7b) that we will use the 2007 best-estimates
envelope against which to set the policy discussion for much of the rest of this topic.
Specifically, the discussion will be compared with what we know actually happened
from palaeoclimatic indicators of the real Earth (and not an expensive computer
model) at times of past warming and from when it was actually warmer than today.
The former is analogous as to how biomes react to warming (climate change), whereas
the latter is analogous to where we are heading with global warming.
These various IPCC scenario forecasts all portray a similar picture but because there
were four IPCC assessments up to 2007 (and a fifth is due in 2013), when looking at
the various assessment scenario forecasts together it can be a little confusing. So, it
might be helpful to bring all the IPCC assessment Business-as-Usual scenarios (1990-
2007) together.