Geoscience Reference
In-Depth Information
There is evidence from observational data that weather and climate extremes have
changed since 1950 due to the human impact on the climate system (IPCC
2012a
).
The latest IPCC Working group I report confi rms these fi ndings (IPCC
2013
).
Cold days and nights have decreased, whereas warm days and nights have
increased. This is based on a global scale and on land data only (IPCC
2013
). Heat
waves frequency has increased in most areas of Europe, Asia, and Australia (IPCC
2013
). Further, a statistically signifi cant increase in heavy precipitation events (e.g.,
95th percentile) has been detected in many regions. This is consistent with the
increase in temperature and the observed rise in atmospheric water vapor (IPCC
2007a
). Europe and North America experienced increased frequency and intensity
of heavy precipitation events (IPCC
2013
). However, there remains great variation
within the precipitation trends depending on the region (IPCC
2012a
).
The trends are less consistent for droughts, fl oods, and cyclone activity (IPCC
2012a
) (see Sect.
2.2.4
for a targeted section about tropical cyclone activity). Some
regions, for example, have shown more intense and longer drought periods (e.g.,
southern Europe, West Africa) others have shown a decline (e.g., Central North
America) (IPCC
2012a
).
2.2.3
Future Trends
Confi dence of future projections of climate and weather extremes depends on a
variety of factors, including the uncertainty inherent to future climate simulations
(e.g., uncertainty related to climate sensitivity and choice of scenarios), the type of
extreme events, the temporal and spatial scale of events, and the ability of models to
describe the key underlying processes. Historical data availability plays a critical
role as well (IPCC
2012a
).
A portion of the uncertainty in future predictions is epistemic (“knowable
unknowns”) and may be reduced through further model development and data avail-
ability. There is some level of stochastic uncertainty (“unknowable unknowns”),
however, which may be insensitive to further scientifi c efforts.
Despite the uncertainty, there is scientifi c consensus on the overall future trajec-
tory of some weather and climate extremes. Extreme temperatures and precipitation
events are anticipated to increase under a warming climate (Peterson et al.
2012
).
Model projections assess that the returning period of extreme hot days and heat
waves will increase. A hottest day that used to occur once every 20 years is likely to
occur once every other year by the end of the twenty-fi rst century in most areas
around the globe (IPCC
2012a
). Also projected to increase are the length, frequency,
and/or intensity of heat waves (IPCC
2013
). It is important to note that cold extreme
events will continue to happen (IPCC
2013
). Extreme hot and cold days can, for
example, infl uence the mortality rate in cities. A recent study by Li et al. (
2013
)
forecasts an increase in net temperature (heat- and cold-) related deaths for
Manhattan, New York, by 2080 of more than 15 %.
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