RECENT CLIMATE CHANGE AND
TRENDS IN GLOBAL
STORMINESS
Talk Structure
Discussion of trends in storminess over
the last 40 years and future projections.
Tropical Cyclones
US Tornadoes
European Winter Storms
Economic and Societal Impacts
Adapted from Munich Re Data
Hurricane Ike Damage
(Galveston Island)
Tropical Storm Allison
(2001) Houston Flooding
Global Temperature Trend
1880-2012
Tropical Cyclones
Background
A tropical cyclone is a warm-centred low pressure
system which is non-frontal, occurs in tropical and
sometimes subtropical waters, and has a closed low
level wind circulation.
During it’s life a tropical cyclone may grow from a
tropical depression to a tropical storm or, if it
strengthens enough, through to a full blown hurricane.
It is wind speed alone which determines the tropical
cyclone’s category.
Regional Occurrence
Structure of a Hurricane
Saffir-Simpson Hurricane Wind Scale
} Major or Intense Hurricane
U.S. Tropical Cyclone Damage 1925-1995(Pielke and Landsea, 1997)
Storm
Category
Winds
(mph)
Surge
(ft)
Mean
Damage($ millions)
Potential
Damage
Percent
Total
Damage
Tropical
Storm (118)40-74 2-3 59 0 2.0%
Hurricane
Cat. 1 (45)74-95 4-5 624 1 8.3
Hurricane
Cat. 2 (29)96-110 6-8 698 10 6.0
Hurricane
Cat. 3 (40)111-130 9-12 2,978 50 35.0
Hurricane
Cat. 4 (10)131-155 13-18 15,358 250 45.2
Hurricane
Cat. 5 (2)>155 >18 [5,973] 500 3.5
US Damage by Storm Category
In the U.S., major hurricanes account for only 21% of hurricane landfalls but 83% of hurricane damage.
2004 Hurricane Season
2005 Hurricane Season
Hurricane Intensity
Webster et al. (2005)
in a paper in Science
show that:
The number of Cat 4
and 5 strength
hurricanes
worldwide has
increased from
about 11 per year in
the 1970s to 18
annually now.
Global Tropical Storm and
Hurricane Numbers (12-month running totals)
Source: http://models.weatherbell.com/tropical.php
Global Hurricane and Intense
Hurricane Numbers (12-month running totals)
Source: http://models.weatherbell.com/tropical.php
Global Accumulated
Cyclone Energy Index (12-month running totals)
Source: http://models.weatherbell.com/tropical.php
Future Projections
• Likely the global frequency of tropical cyclones
will either decrease or remain essentially the
same by 2100.
• Likely increase in tropical cyclone-related
rainfall rates (+3% to +37%, typically +20%
within 100km of the storm centre).
• Some increase in the mean maximum wind
speed of tropical cyclones is likely (+2% to
+11% globally).
Knutson et al., Nature Geoscience, Feb 2010. Tropical cyclones and
climate change.
U.S Tornadoes
Numbers of Strong-to-Violent
(F3-F5) US Tornadoes 1950-2007
No upward trend exists
European Windstorms
European Winter Storms
Porthleven, Cornwall: 4 Jan 1998 (Courtesy, Simon Burt)
European windstorms
caused damages of US $ 2.8
bn per year 1990-1999
Rank as the 2nd highest
cause of global insured
losses after US hurricanes
Dynamics
Most European windstorms are caused by North Atlantic
extratropical low pressure systems.
These systems gain their energy from horizontal
temperature contrasts between cold, polar air masses
and warm, subtropical air masses.
Since the latitudinal temperature contrasts between
these air masses is greatest during winter, the frequency
and intensity of European windstorms peak during this
season as well.
European windstorms occur between October and
March with a peak incidence in January.
Storm tracks are ‘steered’ by the jet stream.
Dynamics (2)
Windstorm Oratia (28th October 2000)
Peak gusts around 100 mph
Central pressure 951mb
(deepest recorded October
low in UK)
Occurred one year after
damaging windstorms
Lothar and Martin struck
France with similar
intensity.
"We have to realise that this almost certainly
has climate change as a contributory cause.“ (Environment minister Michael Meacher)
"We are seeing increasing evidence that climate change
may be impacting on our environment.“
(Environment Agency's head of operations, Archie Robertson)
“The storms and floods we are now seeing will get
more frequent and more severe.”
(Roger Higman, Friends of the Earth)
Why Winter Storm Incidence May
Change
Zonal mean temperature change by 2100
Data Source
Use gridded climate data for the region 35-70oN, 15oW-30oE to
calculate number of days each year during the period (Oct-Mar)
with Storm Force 10 (55+ mph sustained) wind speeds and
seasonal Accumulated Wind Power Index.
Number of Beaufort Force 10
Days over Europe/N Atlantic
Accumulated Wind Power
Index over Europe/N Atlantic
Change in Number of NH Storms
per Winter by 2100
UKMO
OBS
UKTR HadCM2 HadAM3P
depth control Change
2xCO2
control Change
IS92a
CON
1960-
1990
Change
SRES
A2
deep
Pc<970
22.4 18.5 0.4 21.68 6.92
(99%)
32.37 2.38
(99%)
medium
970<Pc<
1000
68.5 79.8 7.2 98.88 -4.82
(99%)
91.73 -3.34
(95%)
shallow
Pc>1000
33.5 39.8 -4.8 44.08 -11.33
(99%)
37.87 -3.69
(99%)
total 124.4 138.1 2.9 164.63 -9.23
(99%)
161.97 -4.66
(99%)
NAO Considerations
+ve NAO -ve NAO
(Figures Courtesy of Martin Visbeck, Columbia University)
NAO Winter Index 1825-2012
(Figure Courtesy of Tim Osborn, University of East Anglia)
Relationship Between Storminess
and NAO (1971-2012 data)
Summary
There is little evidence for any global warming-
induced upward trend in global windstorms over
the last 40 years.
Most recent research suggest little change or a
decrease in storm frequency with a modest
increase in the frequency of the most intense
storms.
The biggest influence on storm-related casualties
and losses, at least in the near future, will come
from natural climate variability.
Questions?