The Precautionary Principle 229especially of the more devastating possibilities. Although covering our-
selves for the most unlikely happenings is not our main reason for taking
out the insurance, our peace of mind is considerably increased if the
policy includes these improbable events. In a similar way, in arguing for
action concerning global warming, some have strongly emphasised the
need to guard against the possibility of surprises (see examples in Table
7.4). They point out that, because of positive feedbacks that are not yet
well understood,^7 the increase of some greenhouse gases could be much
larger than is currently predicted. They also point to the evidence that
rapid changes of climate have occurred in the past (Figures 4.6 and 4.7)
possibly because of dramatic changes in ocean circulation; they could
presumably occur again.
The risk posed by such possibilities is impossible to assess. It is,
however, salutary to call attention tothe discovery of the ozone ‘hole’
over Antarctica in 1985. Scientific experts in the chemistry of the ozone
layer were completely taken by surprise by that discovery. In the years
since its discovery, the ‘hole’ has substantially increased in depth. Re-
sulting from this knowledge, international action to ban ozone-depleting
chemicals has progressed much more rapidly. Ozone levels are begin-
ning to recover – full recovery will take about a century. The lesson for
us here is that the climate system may be more vulnerable to disturbance
than we have often thought it to be. When it comes to future climate
change, it would not be prudent to rule out the possibility of surprises.
However, in weighing the action that needs to be taken with regard
to future climate change, although the possibility of surprises should be
kept in mind, that possibility must not be allowed to feature as the main
argument for action. Much stronger in the argument for precautionary
action is the realisation that significant anthropogenic climate change is
not an unlikely possibility but a near certainty; it is no change of climate
that is unlikely. The uncertainties that mainly have to be weighed lie in
the magnitude of the change and the details of its regional distribution.
An argument that is sometimes advanced for doing nothing now is
that by the time action is really necessary,more technical options will be
available. By acting now, we might foreclose their use. Any action taken
now must, of course, take into account the possibility of helpful technical
developments. But the argument also works the other way. The thinking
and the activity generated by considering appropriate actions now and
by planning for more action later will itself be likely to stimulate the sort
of technical innovation that will be required.
While speaking of technical options, I should briefly mention poss-
ible options to counteract global warming by the artificial modification
of the environment (sometimes referred to as geoengineering).^8 A num-
ber of proposals for ‘technical fixes’ of this kind have been put forward;