Geoscience Reference
In-Depth Information
it was virtually certain that increases in the frequency and magnitude of warm daily
temperature extremes and decreases in cold extremes will occur in the 21st century
on the global scale. Also, it is very likely that the length, frequency and/or intensity of
warm spells, or heatwaves, will increase over most land areas. Based on the IPCC's
A1B and A2 emissions scenarios, a 1-in-20-year hottest day is likely to become a
1-in-2-year event by the end of the 21st century in most regions. Additionally, average
tropical cyclone maximum wind speed is likely to increase, although increases may
not occur in all ocean basins. However, it is likely that the global frequency of
tropical cyclones (hurricanes and typhoons) will stay roughly the same or decrease.
As for the damage that climate extremes will bring, the SREX concluded with high
confidence that disaster losses associated with weather, climate and geophysical events
are higher in developed countries. Fatality rates and economic losses expressed as a
proportion of GDP are higher in developing countries. Here the IPCC have a specific
meaning for the words 'likely', having a notional probability of 66-100%, and 'high
confidence', that there is high agreement from a body of robust evidence. Of course,
it should be remembered (in case you are reading this in the decades to come) that
what is considered an extreme event early in the 21st century will be more normal
(frequent) towards the century's end when the characteristics of extreme events will
be even more extreme. Finally, the IPCC are careful to stress that they draw the
above conclusions in general and not specifically: that is to say, it is impossible to
distinguish the cause of a specific extreme event between climate change on one hand
or the vagaries of weather on the other. So, from the IPCC perspective in 2011 it would
be impossible to sue a fossil fuel company for the damages caused by a heatwave or
a hurricane.
The agricultural and health impacts of such extreme weather events will be con-
sidered in the next chapter.
6.6.2 Greenhousegases
The IPCC scenarios are based on a number of global economic possibilities ranging
from business as usual to prudent policies curbing emissions and introducing new
low-fossil and/or alternative technologies. These, from the later 2001 reports, result
in a range of predictions (see Figure 5.7). Fortunately, for simplicity the clear majority
of these fall within the high and low estimate boundaries of the IPCC's original 1990
Business-as-Usual (B-a-U) scenarios (Figure 5.5 and Table 5.1). Yet, even so, there
may be surprises. For example, these models assume that the biosphere's response
tomorrow to additional atmospheric carbon dioxide will be proportionally similar
to the response today. But what if some threshold were reached? It may be that
circumstances are such that the oceans cease to absorb as much of this additional
carbon as they have done in the past. (Perhaps because increasing acidity means that
the oceans are unable to buffer so much carbon dioxide, as will be discussed shortly.)
In such a case the build-up of atmospheric carbon dioxide would be greater than
expected and, as a result, so would climate change. Alternatively, if natural (as opposed
to human) systems do operate as expected then there may be unforeseen developments
in human systems. Then again, what would happen if China's population of 1.3 billion
people were to start increasing their fossil fuel consumption at rates previously not
 
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