238 Weighingthe uncertainty
Other items, some of which were mentioned at the end of Chapter 7,
such as natural amenity and the value of species, can also be considered
as ‘natural’ capital. I have argued (Chapter 8) that there is intrinsic value
in the natural world – indeed, the value and importance of such ‘natural’
capital is increasingly recognised. The difficulty is that it is neither pos-
sible nor appropriate to express much of this value in money. Despite
this difficulty, it is now widely recognised that national and global indi-
cators of sustainable development should be prepared that include items
of ‘natural’ capital and ways of including such items in national balance
sheets are being actively pursued.
In summary, the items in the overall global warming balance sheet
that have been identified are:
Estimates of cost (for those items which can be quantified in terms of
money) of the likely impacts of anthropogenic climate change. Most
of the estimates to date have costed the impacts supposing the equiva-
lent atmospheric carbon dioxide concentration were to double (which
could occur during the second half of the twenty-first century). When
some allowance is also included for the costs of extreme events (see
Chapter 7, page 179) they are typically around one to two per cent
of GDP in developed countries and typically five per cent or more in
developing countries.
Estimates of the cost of adaptation to anthropogenic climate change.
Significant levels of adaptation will be required to the substantial de-
gree of climate change to which the world is already committed. Even
if the maximum possible mitigation takes place, because of the long
time constants of change, the requirement for adaptation will continue
for many centuries into the future, for instance to respond to the sea
level rise that will continue for many centuries. Very few estimates
have, as yet, been made of adaptation costs, although a few such costs
are included in some of the impact studies.
Estimates of the impacts of anthropogenic climate change that are diffi-
cult if not impossible to value in money terms; for instance, those with
social consequences, those that affect human amenity and ‘natural’
capital or those that have implications for national security.
Estimates of the cost ofmitigation of anthropogenic climate change.
For reductions in emissions leading to stabilisation of atmospheric
carbon dioxide concentration (even at a level as low as 450 ppm –
doubled pre-industrial carbon dioxide is 560 ppm) these are typically
less than one year’s economic growth by 2050.There is already international acceptance that action to mitigate
global warming is necessary. Such ‘weighing’ of the economics as has
been possible so far brings two messages – that action must begin now to