Sustainability and policy - Climate Change: Biological and Human Aspects - page 513

National interest-rate
changes

Every 3 months or so

National budget About 12 months or so

Political term of office About 5 years

8 years

Apollo space programme

Depleting an oil field Two decades or so

A few
decades

Planting a tree to
maturity
Planting trees to
development of
near-climax ecology

Centuries

Atmospheric residence
time of a CO 2 molecule

One to two
centuries

Time

Fig. 8.11 Timehorizonsofvarioushumanactivities,naturalprocessesandatmosphericcarbondioxide.Thepolitical

timehorizonisprimarilydictatedbythelengthoftermofoice,whichisafewordersofmagnitudelessthan
manyenergy-relatednaturalprocesses;thistimehorizon(theshadedareaintheigure)isalsothetypical
periodof direct policyinvolvement(responsibility).ReprintedfromCowie(1998a).

released into the atmosphere is of a similar magnitude to that involved in the Eocene
event. Yet this similarity exists and was noted by the IPCC's 2007 assessment report 5 .
Computer models as yet do not include the necessary biospheric components needed
to simulate such events with sufficient detail/confidence, but they probably will in
time. However, the evidence that does exist seems to point to an Eocene-maximum-
type possibility. This suggests that future global warming impacts are likely to be
very significant, especially in the long term from the point of view of humans.
Here the language and perceptions of scientists and policy-makers varies. Geolo-
gists commonly view matters in thousands to tens of millions of years and longer.
Such timescales do not figure in policy-makers' operational perceptions. For them 2 or
3 years is short term and a decade or more is long term. Even the timescale of short-
term climate science processes tends to be greater than that which policy-makers
usually consider (see Figure 8.11).
Reconciling these two sets of perceptions is not easy. Consequently biosphere
scientists need to recognise that their long-term concerns will not be readily (if
at all) appreciated by policy-makers and so the scientists will need to adjust their
presentations of science to politicians. Yet climate change and its associated impacts
will be very significant on both these levels.
On the decade level we will see significant change and impacts. For example, over
the coming years parts of the Earth (be it parts of the USA or the UK or South Africa)
will become markedly drier, with profound economic and ecological effects. Over the
coming couple of decades past weather extremes, such as the heatwaves experienced

5

The IPCC AR4 (2007) can be accessed from the IPCC website and chapter 6 of the Working Group
I The Physical Science Basis report (IPCC, 2007c), entitled Palaeoclimate, is freely available in both
HTML and PDF formats. See the report's pp. 442-3.