Environmental Engineering Reference
In-Depth Information
predict dramatic dying in parts of sub-Saharan Africa, but others do not.
Patterns of precipitation changes in middle and higher latitudes are more
robust on large scales but remain uncertain on the regional scales of im-
portance for impact and adaptation strategies. For example, the changes in
precipitation in the western United States in wintertime are sensitive to the
El Niño phenomenon in the equatorial Pacific, the response of which is itself
uncertain. And especially over semi-arid land surfaces, arguments based
on the assumption that relative humidities do not change can break down.
Given these complexities, we consider the CMIP3 ensemble as providing our
best estimates of the pattern of precipitation change accompanying global
warming, with consistency or inconsistency across this ensemble provided
some indication of uncertainties.
4.3 HURRICANES
Atlantic Hurricanes
Atlantic hurricane activity has increased markedly in the past 20 years,
concurrent with increases in ocean temperatures in the tropical North At-
lantic region in which hurricanes are formed. But it is well established that
hurricane frequency is dependent on other aspects of the large-scale climate
as well as the local ocean temperatures. Many of the issues regarding detec-
tion, attribution, and projection of tropical cyclone trends in the Atlantic
and throughout the tropics have recently been assessed by a WMO expert
team (Knutson et al., 2010). We highlight a few of these issues here, basing
the discussion in large part on this recent assessment, and refer the reader
to Knutson et al. (2010) for a more detailed discussion.
Several detailed studies of the tropical storm record in the Atlantic have
converged on a consensus view that the recent trend is more likely due to
internal multi-decadal variability than a part of a century-long trend associ-
ated with greenhouse gas increases. While the raw data for Atlantic storms
suggest a significant century-long trend, three separate lines of analysis cast
doubts on the reality of this trend: (1) the frequency of landfalling storms, for
which the completeness of the data is less of an issue than for basin-wide
statistics, shows no significant long-term trend (Landsea, 2007); (2) estimates
based on historical ship tracks indicate enough storms were likely missed
in the early part of the century to account for most of the long-term trend
in storm frequency (Chang et al., 2007; Vecchi and Knutson, 2008); and
(3) the long-term trend in the raw data is primarily from short-lived storms
(<3 days), which also suggests data artifacts are dominating the long-term
