8.4 Occurrence of Extreme Events
Climate change includes both variations in the mean climate variables as well as in
weather extremes. Overall, by definition, an extreme event refers to an event that is
rare in a specific place and time of the year. A rare phenomenon is one that may
occur with probabilities equal to or less than the 10th percentile or equal to or
greater than the 90th percentile, considering a probability density function derived
from real data. If the pattern of extreme climate anomalies persists over a large
period, such as a season, resulting in an extreme average, then it can be classified as
an extreme climate event (AR5 Report).
Over the last 60 years, some global extreme events have increased in magnitude
and frequency. These include heatwaves and intense precipitation, on different
spatiotemporal scales, with unevenly distributed change profiles (e.g., Perkins et al.
2012; Coumou and Rahmstorf 2012).
The distribution of daily maximum and minimum temperatures has shifted to
higher temperatures, with changes of variances in probability distribution functions
showing a spatial heterogeneity, with wider distributions in the tropics. Global
trends in night-time temperature events were stronger than those relative to daytime
(Donat and Alexander 2012; Perkins et al. 2012; Donat et al. 2013).
The National Weather Service (NWS) in the USA defines, in a simple way
(Robinson 2001), a heatwave as a period lasting at least 48 h wherein neither the
overnight low nor the daytime high falls below the thresholds of 26.6 and 40.5 °C,
respectively. When more than 1% of the recorded case values in automatic weather
stations exceed NWS thresholds, alternative heatwave thresholds are defined as the
values of these 1% cases. In general, a hot spell is a similar event referring to events
ranging from the 1% values to the NWS thresholds, while a warm spell is an event
occurring between the 1 and 2% values.
Extreme events, such as a decrease in cold temperature extremes, increase in
warm temperature extremes, sea-level changes, discrete heavy precipitation events,
or drought increase in dry areas, have been observed since the 1950s and many
were linked to anthropogenic influences (AR5 Report). The frequency of heatwaves
has increased in continental areas in Europe, Asia, and Australia, and there is a
strong chance that human influence more than doubled the probability of heatwave
events in some areas. Extreme diurnal patterns as warm days and nights increased,
with high likelihood, at the expense of cold days and nights.
Global field observations over the second half of the twentieth century validated
the likely human influence on the increase in heavy precipitation events. Costs
related to flood damage worldwide have been increasing since the 1970s, with the
risks of extreme events and/or related processes increasing with further warming,
even if only by 1 °C.
Negative impacts of extreme climate events include disruption of food crops and
water availability, deterioration of infrastructures, and human health and lives. The
inability to cope with these drastic impacts applies to some extent to all countries
regardless of their developmental status (e.g., Meehl et al. 2000; AR5 Report).
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8 Fundamentals of Global Carbon Budgets and Climate Change
Climate change includes both variations in the mean climate variables as well as in
weather extremes. Overall, by definition, an extreme event refers to an event that is
rare in a specific place and time of the year. A rare phenomenon is one that may
occur with probabilities equal to or less than the 10th percentile or equal to or
greater than the 90th percentile, considering a probability density function derived
from real data. If the pattern of extreme climate anomalies persists over a large
period, such as a season, resulting in an extreme average, then it can be classified as
an extreme climate event (AR5 Report).
Over the last 60 years, some global extreme events have increased in magnitude
and frequency. These include heatwaves and intense precipitation, on different
spatiotemporal scales, with unevenly distributed change profiles (e.g., Perkins et al.
2012; Coumou and Rahmstorf 2012).
The distribution of daily maximum and minimum temperatures has shifted to
higher temperatures, with changes of variances in probability distribution functions
showing a spatial heterogeneity, with wider distributions in the tropics. Global
trends in night-time temperature events were stronger than those relative to daytime
(Donat and Alexander 2012; Perkins et al. 2012; Donat et al. 2013).
The National Weather Service (NWS) in the USA defines, in a simple way
(Robinson 2001), a heatwave as a period lasting at least 48 h wherein neither the
overnight low nor the daytime high falls below the thresholds of 26.6 and 40.5 °C,
respectively. When more than 1% of the recorded case values in automatic weather
stations exceed NWS thresholds, alternative heatwave thresholds are defined as the
values of these 1% cases. In general, a hot spell is a similar event referring to events
ranging from the 1% values to the NWS thresholds, while a warm spell is an event
occurring between the 1 and 2% values.
Extreme events, such as a decrease in cold temperature extremes, increase in
warm temperature extremes, sea-level changes, discrete heavy precipitation events,
or drought increase in dry areas, have been observed since the 1950s and many
were linked to anthropogenic influences (AR5 Report). The frequency of heatwaves
has increased in continental areas in Europe, Asia, and Australia, and there is a
strong chance that human influence more than doubled the probability of heatwave
events in some areas. Extreme diurnal patterns as warm days and nights increased,
with high likelihood, at the expense of cold days and nights.
Global field observations over the second half of the twentieth century validated
the likely human influence on the increase in heavy precipitation events. Costs
related to flood damage worldwide have been increasing since the 1970s, with the
risks of extreme events and/or related processes increasing with further warming,
even if only by 1 °C.
Negative impacts of extreme climate events include disruption of food crops and
water availability, deterioration of infrastructures, and human health and lives. The
inability to cope with these drastic impacts applies to some extent to all countries
regardless of their developmental status (e.g., Meehl et al. 2000; AR5 Report).
282
8 Fundamentals of Global Carbon Budgets and Climate Change