The document discusses various extreme weather events, including heat waves, droughts, and tropical storms, highlighting trends in their frequency and intensity due to climate variability and human-induced climate change. Data shows significant increases in high temperatures and warm nights, while the incidence of cold conditions has decreased. Furthermore, it notes that extreme precipitation events and floods have become more frequent, with severe impacts observed in various regions, particularly during events like the 2010 Pakistan floods.

1. Extreme weather events
Heat and
cold waves
Drought
Tropical
storms
Heavy rains
Photograph: Stringer
Shanghai/Reuters
An extreme weather event is the occurrence of a value of a weather variable above (or below) a
threshold value near the upper (or lower) ends of the range of observed values of the variable. These
events are not a sign of climate change by itself, as they always existed but the occurrence and
severity of at least some of these events have increased.
1
Data collection
and presentation
by Carl Denef,
Januari 2014

2. Land summer temperature distribution has shifted
 From 1951 to 1961, only 1% of the land area in the Northern Hemisphere was
exposed to temperatures higher than 3 standard deviations (SD) from the mean for
1951–1980. But from 2001-2011, 11% of land area was exposed to temperatures
higher than 3 SD away from the average. About 1% of land area, an area twice the
size of France, experienced heat extremes of 5 SD from the mean. The same trend is
seen in the Southern Hemisphere.
2

3.  The annual frequency of warm nights (90th percentile) and warm days (90th percentile)
for the period 1950-2010 is increasing, relative to the period 1961 to 1990, in many regions
of the World. The same trend is seen in decadal values (right panel). Occurrence of warm
nights is more widespread than that of warm days. From IPCC AR5 Figure 2.32.
Extreme high temperatures become more frequent
The Figure shows 3 datasets: HadEX2; HadGHCND and GHCNDEX
3

4.  In contrast, the incidence of cold days and nights (10th percentile of temperatures) have
decreased. From IPCC AR5 Figure 2.32
4

5.  Also in Europe the number of hot days
since 1960 have increased.
 In the Figure higher confidence in the
long-term trend is shown by a black dot.
From European Environment Agency
5

6. Warmest day of the year
 Between 1951 and 2010 there was a
robust rise in the temperature value of
the warmest day of the year in many
areas of the World. The trend was up to
>1 °C per decade. This means up to 10
°C in some areas From IPCC AR5 Box
2.4, Figure 1.
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7. Heat waves
 Heat waves are often associated with quasi-stationary anticyclonic circulation anomalies
that produce prolonged hot weather. Heat waves can be amplified by pre-existing dry soil
conditions, induced by precipitation deficits or evapotranspiration excesses, such as in the
extreme summer heat waves in southeastern Europe.
 According to IPCC AR5, there is “only medium confidence that the length and frequency
of warm spells, including heat waves, has increased since the middle of the 20th century.
The confidence is medium due to lack of data in Africa and South America. However, it is
likely that heat wave frequency has increased during this period in large parts of
Europe, Asia and Australia.”
 Several high-profile heat waves have occurred in recent years (e.g., in Europe in 2003,
Australia in 2009, Russia in 2010 and USA in 2011/2012. With high confidence, Hansen et
al. (2012)[47] attributed the 2010 Moscow and 2011 Texas heat waves to human-
induced global warming , although Dole et al. (2011)[48] concluded that the 2010 Moscow
heatwave was mostly due to natural climate variability.
 As reviewed in the journal Science, april 2011, 332:220-224, the summer of 2003 was
exceptionally hot in western and central Europe, causing around 70,000 heat-related
deaths. In summer 2010, many cities in eastern Europe recorded extremely high mean
temperature: 38.2°C in daytime in Moscow, 25°C at night in Kiev, and 26.1°C day
average in Helsinki. Russia counted 55,000 deaths, an annual crop failure of ~25%, more
than 1 million hectares a of burned area, and ~$15 billion of total economic loss (~1% of
gross domestic product). During the same period, parts of eastern Asia also experienced
 7

8. extremely warm weather, while Pakistan was hit by devastating monsoon floods.
 The European 2010 summer temperature anomaly was +1.8°C, i.e. 3.5 standard
deviations difference relative to 1970–1999. Further, hottest summers occurrence
stands substantially above any other 10-year period since 1500 (see Figure next
slide). At least two summers in this decade have been the warmest of the last 510
years in Europe.
 It should be noted, on the other hand, that there is also evidence that periods prior to
the 1950s had more heat waves in some regions (e.g., over the USA during the 1930s
decade, while in other regions heatwave trends may have been underestimated due to
poor quality and/or consistency of data (e.g., over Western Europe and over the
Mediterranean).
 In South America, Africa, Middle-East and South-East Asia, there is low confidence or
insufficient evidence (lack of data) for any change. In other parts of Asia the trends
are variable, but there are more regions of increase in heat waves than decrease.
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9.  The Figure shows the statistical
frequency distribution of
european summer land
temperature anomalies for the
1500–2010 period (vertical
lines). Anomalies in °C relative
to the 1970–1999 period are
shown in X-axis, and the
individual summers are
represented by the vertical lines.
The 5 warmest and coldest
summers are highlighted. The
Gaussian fit is in black. As can
be seen the 5 hottest summers
all fall in the last decade.
 Bottom shows the decadal
frequency of summers with
temperature above the 95th
percentile of the 1500–2002
distribution.
European summer temperatures for 1500–2010, constructed from
instrumental and proxy data.
From Science, april 2011, 332:220-49

10.  Europe was again unusually hot in July-August 2013. The map shows average
surface temperature anomalies between July 16 and August 11, 2013, compared to
the 1981-2010 average for the same time of year. Austria had its record highest ever
(40°C) on August 8.
Source10

11. Record high and low temperatures in the U.S.
 As shown in the Figure below, record Highs now outpace record Lows by 2:1, as
observed at about 1,800 weather stations in the 48 contiguous United States from
January 1950 through September 2009. Meehl et al. 2009 Read more
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12. Droughts
 Long-term droughts (persisting for periods up to a decade or longer) are a recurring feature of
Holocene paleoclimate records in North America, East and South Asia, Europe, Africa and India.
The transitions into and out of the long-term droughts take many years. These events are natural
and since the long-term droughts all ended they are not irreversible.
 Several recent studies suggest that regional reductions in precipitation are primarily due to
climate variability and that man-caused trends are currently weak.
 To measure drought conditions the Palmer Drought Severity Index (PDSI) is used on a scale of
zero (normal rainfall) to -4 (extreme drought). It is used also for wet spells, in which case
positive numbers are used. It is calculated from a simple water-balance model including monthly
precipitation and temperature data. The global very dry areas were found doubled since the
1970s, consistent with decreases in regional precipitation and of increasing evaporation due to
global warming.
The Figure shows the increasing
trend in regional cumulative deficit
in surface land moisture (relative to
local mean conditions) as well as
the global PDSI between 1900 and
2002.
Figure from IPCC AR4
12

13.  Recently, however, scientists at Princeton University
showed that the PDSI overestimates drought trends
because the model relies too much on surface
temperature, that itself is increasing due to climate
change[Ref] . They developed a new model that
included inputs such as solar radiation, humidity and
wind. The Figure shows drought condition trends over
the past 60 years (1950–2008), made up with the
mentioned method. Red areas indicate increasing
levels of drought while blue areas are less prone to
dry conditions. Drought changes are small.
 According to IPCC AR5, observed trends in drought
or dryness (lack of rainfall) since the middle of the
20th century have low confidence at a global-scale,
due to lack of direct observations, geographical
inconsistencies in the trends, and dependencies of
trends quantitation on the index choice. However, it is
likely that the frequency and intensity of drought
has increased in the Mediterranean and West
Africa and decreased in central North America and
north-west Australia since 1950.
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14. Lake shrinkage and decreased river flow
 Top: The Cheyenne Bottoms Wildlife
Wetlands in Kansas. The region was
dramatically impacted by the drought in 2012.
There was sufficient water in the wetland area
in 2010, but the levels began to diminish in
2011. By mid-July 2012, virtually all the water
had evaporated. The area has provided a
resting place for millions of migrating birds
every fall.
Images taken by Landsat 5 and Landsat 7.
Source: U.S. Geological Survey (USGS)
Landsat Missions Gallery, U.S. Department of
the Interior / USGS and NASA.
 Bottom: Bahr al Milh (Lake Razazah) in
Iraq. This is a salt lake, fed by the Euphrates
River. Water levels have been drastically low
year-round in the past decade.
Images taken by Landsat 5, Landsat 7, and
Landsat 8. Source: U.S. Geological Survey
(USGS) Landsat Missions Gallery U.S.
Department of the Interior / USGS and NASA.
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15. Reservoir shrinkage
 The photo shows Boulder Basin, the western part of Lake Mead, in Nevada/Arizona.
Lake Mead is one of the largest reservoirs in the World, supplying water to California,
Arizona, Nevada and Mexico. Since 2000 the water level has been dropping at a fairly
steady rate due to lower snowfall. As of July 2010, the lake is at 38 % of its capacity.
Between January 2001 and April 2004, the water level dropped 18 m.
January 30, 2001 April 28, 2004
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16. Tropical cyclones (typhoons, hurricanes, tornados)
 A tropical cyclone is a rapidly-rotating storm system characterized by a low-pressure center,
strong winds, and a spiral arrangement of thunderstorms that produce heavy rain. Tropical
cyclone generation relies upon several meteorological conditions. Local sea surface
temperatures must be around 26.5 °C. Evaporation from warm surface waters creates high
humidity in the atmosphere, and then leads to thunderstorm development. If multiple
thunderstorm systems converge, a storm with a vortex movement develops. The vortex takes
additional heat and water vapor from the surface of the ocean and releases it into the atmosphere
in the form of rainfall. High winds are created. The more heat available at the surface, the higher
the potential winds. Once wind speeds exceed 55 km/h, the system becomes a tropical storm
and is assigned a name.
Distribution of average sea surface temperature (SST) over
the globe
Tropical storm seen from Space
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17.  On the basis of the role of sea surface temperature on the severity of the cyclone, it can be
expected that global warming may facilitate the incidence and/or severity of tropical
cyclones. A 2005 study published in the journal Nature examined the duration and
maximum wind speeds of each tropical cyclone over the last 30 years (Nature. 436:686-
688) and found that their destructive power has increased around 70 percent in both the
Atlantic and Pacific Oceans. Another 2005 study (Science. 309: 1844-1846), revealed that
the percentage of hurricanes classified as Category 4 or 5 (the two strongest categories on
the Saffir-Simpson scale) has increased over the same period. A categoty 5 cyclone provokes
≥ 252 km/h wind speeds. Read more about category 5 tropical cyclones here
 The IPCC AR4 also concluded that there is no clear trend in the annual numbers of
tropical cyclones but that there is a significant increase in severity (expressed by the
« power dissipation index ») since 1970. Severity parallels sea surface temperature. Read
more
Source
On November 7, 2013 the category 5
typhoon Haiyan made landfall on the
Phillipines with one-minute sustained winds
of 315 km/h and gusts up to 378 km/h.[24]
These wind speeds made this tropical
cyclone the strongest tropical landfalling
cyclone on record [25]. There were
thousands of death.
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18.  N-Atlantic tropical storms occur in cycles, quiet periods alternating with intense
periods. There is a striking co-incidence with the cycles of AMO (see section on
climate variability). When it is in a warm phase, the tendency is to have a very busy
hurricane period. The opposite occurs in the cool phases,
Source NOAA
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19. Precipitation extremes
 As can be seen in the Figure there is a positive trend in the annual amount of extreme
precipitation (expressed as days above the 95th percentile of precipitation
distribution) in Eastern U.S. and Northern Europe between 1951 and 2010. From
IPCC AR5 Figure 2.33
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20. Extreme one-day precipitation in U.S.
 This figure (from EPA) shows the
percentage of the land area
where a much greater than
normal portion of total annual
precipitation has come from
extreme single-day precipitation
events. The bars represent
individual years, while the line is
a nine-year weighted average.
Data source: NOAA, 2012 4
 An increase is seen during the
last 3 decades
 Read more
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21. Floods
 Heavier rains together with sea level rise, tides and storm surges drive the occurrence
of flood. Floods have become more frequent. Major floods that used to happen only
once in 100 years now take place every 10 or 20 years.
 Look at animated map
Figure From
Data from EM-DAT Data from EM-DAT:
The OFDA/CRED International Disaster
Database – www.emdat.be – Université
catholique de Louvain – Belgium.
Numberofeventsreported
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22. Examples of floods
 Flooding in Pakistan. In summer 2010 the Indus River in Pakistan caused a flood
that was called one of the worst humanitarian disasters in history, as a result of heavy
monsoon rains. More than a million acres were flooded, destroying crops and
devastating cities including Sukkar, Mehar, and Dadu. The number of people directly
affected exceeded 21 million, 1,800 were killed and 10 million left without shelter.
 Almost five million people were affected when heavy rains flooded parts of Baluchistan
[Pakistan], Punjab [India] and Sindh [Pakistan] from mid-September 2012. Persistent
floodwater caused many to get homeless for months. Over a million people who did
return to their villages at the end of 2012, found their homes too badly damaged to
inhabit . Read more here
 Also Oxfam reports: “Disasters escalating four-fold as climate change hits poor
hardest” Read more here
 A list of floods can be seen in Wikipedia
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23. View other slide shows on extreme weather
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