Current warming and likely future impacts - Climate Change: Biological and Human Aspects - page 295

increased summer demand for water would probably stress some parts of the US
water-supply system, while increased heavy precipitation would increase the need
for flood management. These changes would disturb freshwater ecosystems. Some
species (both aquatic and terrestrial) would in all probability adapt to climate change
by shifting their ranges, but invasive species and land use would together undermine
this, resulting in a risk to biodiversity.
There were particular worries expressed for 'rare ecosystems', but not so for
managed ones. Forest growth would possibly increase due to the increase in carbon
dioxide and temperatures, spurring growth; however, some forests would probably
become more susceptible to fire and pests. Then in 2009 the second USGCRP report
added that forest productivity is projected to increase in much of the east, while it
is projected to decrease in much of the west where water is scarce and projected
to become more so. Wherever droughts increase, forest productivity will decrease
and tree death will increase. In addition to occurring in much of the west, these
conditions are projected to occur in parts of Alaska and in the eastern part of the
south east.
With regards to agriculture, the first 2001 report concluded that there was no con-
cern for any decline in food security and the assessment considered that agricultural
profit margins would continue to decline for non-biological reasons. The 2009 report
was less sanguine. It warned that the projected climate change is likely to increasingly
challenge the USA's agricultural capacity to efficiently produce food, feed, fuel and
livestock products. Water supply in some regions was a key concern.
Human health impacts were also noted in the 2001 report, especially in the summer
with heat stress. The 2009 report went further, introducing concerns as to climate
changes' overseas human health impacts possibly threatening US security. It also
emphasised the health impacts of extreme weather events. Now, the USGCRP's 2001
assessment did warn of the likelihood of extreme events but this became more of a
recurring theme in the 2009 report.
The importance of the USGCRP's National Assessment Synthesis Team 2001
report was that not only was it the US Government's first major attempt to have its
science agencies assess the likely impacts of climate change on the nation, but that
it also underpinned the US Department of State's 2002 US Climate Action Report
(covered in Chapter 8).
The 2001 assessment painted a very much broad-brush picture and its 2009 follow-
up corroborated and added detail. This first report's coarseness was due to the coarse
nature of (the then) cutting-edge computer models, which by 2000 had not the
sufficient agreement in terms of forecasting the future to portray a spatial picture with
much certainty. However, the two models (the Canadian model from the Canadian
Climate Centre and the Hadley Centre model from the UK) that the report frequently
referred to did, on a state-by-state scale, give a broadly similar pattern of temperature
change throughout the 21st century, even if in some places they disagreed by a few
degrees Celsius. Conversely the 2009 report's climate projections were more coherent
and broadly speaking chimed with the regional projections given by the 2007 IPCC's
own assessment.
The 2001 assessment had noted that in the past century temperatures across much
of the USA have risen, but the states of, and around, Mississippi and Alabama had