Present climate and biological change - Climate Change: Biological and Human Aspects - page 241

information and discussion is ongoing in the scientific literature and it is likely that
the forthcoming 2013 IPCC assessment will further tweak the 2007 forecasts.
In the greater scheme of things, does such tweaking of warming forecasts matter?
As noted, policy-makers are concerned with a bigger socio-economic and political
picture than the exactness of warming magnitudes. It is of negligible importance to
a government that warming 100 years from now may be half a degree or so more or
less than a current estimate. The key conclusion of importance (to policy-makers)
is that warming is almost certain to take place within such-and-such a range. This
seems sacrilegious to some scientists, who rightly take pride in their work and who in
conversation with politicians in Westminster, or on Capitol Hill, correct policy-makers
when talking about half a degree, or x centimetres of sea-level rise, or whatever. This
point may seem trivial, but it is not. It is increasingly important (and not just regard-
ing climate change) for scientists to have good communications with politicians.
Scientists being pedantic as to the accuracy of the current vogue of predictions, how-
ever scientifically worthy, can give the impression of fact and importance when in
actuality there is greater uncertainty about the detail. In truth there is considerable
uncertainty as to whether a specific number of x degrees warming has taken place
since the Industrial Revolution, let alone whether there will be specific y degrees of
warming in the future. Conversely, there is great certainty as to the bigger picture, of
which we can be confident: the Earth has been getting warmer since the Industrial
Revolution and will continue to do so in the 21st century. Indeed, the IPCC reports
themselves are very good about the various degrees of certainty and confidence they
can attribute to their conclusions, but one has to read the full text and not just the
executive summaries.
For the full range of its SRES scenarios (not just the A2 scenario presented in
Table 5.1) the IPCC 2007 assessment concludes that the Earth will warm by between
1.1 and 6.4 ◦ C above the 1980-99 mean by 2100, and it has considerable confidence
in this. Improved environmental understanding (much of which will come from the
biosciences) and computer modelling (not to mention processing power) will further
refine our view of the future, as indeed will the passage of years. However, the IPCC
has for the past three assessments given one additional key warning, and that is to
be prepared for surprises. We need to be aware that a volcanic eruption, or abrupt
changes in ocean circulation and other events, can happen, and that these will have
considerable climatic consequences that take us outside the IPCC B-a-U scenario and
other scenario forecasts. This may be an unsettling conclusion but in terms of policy
it suggests the need for us to plan for the worst-case scenarios and surprises rather
than easier options (see section 6.6).
It would be prudent - despite it being early days - to consider options outside the
IPCC forecast envelope. So are we moving into an even warmer world than the IPCC
forecast or not? A major volcanic eruption, such as of that underneath Yellowstone
National Park in the USA, would cool the world for several years. However, currently
changes in most of the other probable climate forcing variables are more likely to
force the climate the other way, suggesting that if anything the IPCC forecast is
conservative and that global warming will be greater rather than lesser. (Indeed, even
an out-of-the-ordinary Yellowstone-type event would generate carbon dioxide, the
warming effect of which may well outlast its cooling impacts.) Since 1990, global
temperatures, atmospheric concentrations of carbon dioxide and carbon emissions