Current warming and likely future impacts - Climate Change: Biological and Human Aspects - page 298

but then levelling off or slowing down in the century's final quarter. Either way, the
US gross domestic product (GDP), it was thought, would increase, although there
was considerable uncertainty about how much. Meanwhile the second report noted
that the US population had been estimated to have grown to more than 300 million
people, nearly a 7% increase since the US's 2000 census, and that then current Census
Bureau projections were for this growth rate to continue, with the national population
projected to reach 350 million by 2025 and 420 million by 2050. The highest rates
of population growth to 2025 were projected to occur in areas such as the south west
that are at risk for reductions in water supplies due to climate change.
My purpose in describing the first 2001 USGCRP report and simply noting just
some of the principal points of the second one in 2009, rather than concentrating
on the latter, is to demonstrate two things. First, much is old news and little is new,
even if the updates are extremely useful in their extra detail. All too often in both
science and policy development there is focus on current developments and not how
we got there. In one sense this is regrettable because we then do not see failure in
addressing matters previously raised. Second, by concentrating purely on the latest
reports, those doubtful (or even sceptical) of the science can claim that somehow this
is a re-writing, and that because a re-writing was required it may well be again in the
future, so concerns do not need to be raised seriously. Such a perspective is, of course,
obfuscation. Those beyond science need to appreciate that science really is all about
're-writing', but in an evolutionary sense of it building upon past understanding, and
that it does need to be taken seriously.
Returning to climate change and its consequence for the USA, putting the above
population and wealth forecasts into the context of extreme climatic events such
as hurricanes (which in a warmer world we might reasonably expect to see more
frequently), the 2001 report noted that although the number of hurricanes per year
has been constant in the last century, the number of deaths by hurricanes has declined
(presumably through better facilities affordable in a richer society). Yet, conversely,
property losses from hurricanes increased (presumably because a wealthier society
has more to lose).
That there is a link between climate and the destructiveness of cyclones has become
increasingly apparent. In 2005 Kerry Emanuel from the Massachusetts Institute of
Technology published results based on surface wind measurements taken during
storms over the past 30 years. He found a high correlation between the destructive
potential of storms and sea-surface temperature. He suggested that future warming
might lead to an upward trend in destructive potential and predicted a substantial
increase in hurricane-related losses in the 21st century. Meanwhile, in the same year
Peter Webster, of the Georgia Institute of Technology, and colleagues, including one
from the National Center for Atmospheric Research in Colorado, published a study
covering a 35-year period of cyclone activity. They found no statistical increase in the
global number (frequency) of tropical storms and hurricanes but, in a way affirming
Emanuel's results, a large increase was seen in the number of the most powerful
storms (categories 4 and 5 on the Saffir-Simpson scale).
Over the 35-year study period the number of the most powerful hurricanes had
increased by 80%. Interestingly, the survey showed no statistical increase in the actual
intensity of the most intense hurricanes: the maximum intensity appeared static but