severe weather response to climate change: the expected and the unexpected
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Severe Weather Response to Climate Change: The Expected and the Unexpected. Greg Holland. Regional Climate Research Section NCAR Earth System Laboratory. Collaboration with Cindy Bruyere. NCAR is Sponsored by NSF and this work is partially supported by the - PowerPoint PPT PresentationTRANSCRIPT
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Severe Weather Response to Climate Change: The Expected and the Unexpected
Regional Climate Research SectionNCAR Earth System Laboratory
NCAR is Sponsored by NSF and this work is partially supported by the Willis Research Network, the DOE Research Program to Secure Energy for
America and NSF EASM Grants 1048841 and 1048829
Greg Holland
Collaboration with Cindy Bruyere
• IPCC assessment of extremes and climate change
• Application of EVT to hurricane extremes
• The Anthropogenic Climate Change Index (ACCI)
• Past changes in hurricane extremes, expected and unexpected.
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Summary
“There is evidence that some extremes have changed as a result of anthropogenic influences, including increases in atmospheric concentrations of greenhouse gases.” • likely for extreme maximum temperatures• medium for extreme precipitation• likely for extreme coastal high water• Likely increase in tropical cyclone maximum winds
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IPCC Findings
(IPCC SREX 2012)
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Sensitivity of Extremes
(IPCC SREX 2012)
Quantifiable Through Extreme Value Theory
1
'( )bb x
ab xPDF f x ea a
We utilize the Weibull distribution for which the PDF and Exceedence Probability are:
Where parameters a and b determine the scale and the shape, respectively.
5Holland, ETH October 2012
( { }) 1 ( )bc
aP E x c f c e
The Weibull distribution mean and variance are given by:
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Sensitivity of Extremes
For Atlantic tropical cyclones:• Changes to the mean and standard deviation of 2.5-3 ms-1
(around the observational resolution) results in:• 100-150% increase in Cat 4-5 and • 200-300% increase in Cat 5.
(Holland and Bruyere 2012)
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An Example: Melbourne Australia Temperatures
http://ckrao.files.wordpress.com/2011/12/spring-in-melbourne1.jpg
Maximum Temperatures
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Assessing Extremes from Low-Resolution Models
Wind speed distribution shifting to right
Projected increase in TC intensity, but model can only
resolve up to Cat 2.
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Future Hurricane Extremes
Very similar results from using GPD instead of Weibull
(Holland and Suzuki 2012)
2020-2030 2045-2055-10
0
10
20
30
40
50
60
70
Base: 1980-1994
PE69 PE58 PE48Period
% c
hang
e in
pro
babi
lity
Cat5
Cat4
-5 Cat3
-4-5
All H
urric
anes
Intense Hurricanes Likely to Increase with Global Warming (IPCC, WMO)
That Global Warming has Already Occurred is Unequivocal (IPCC)
No Evidence for Current Hurricane Changes?(IPCC WMO)
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A Conundrum
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Weather Impacts Have Increased
“Global weather-related losses in recent years have been trending upward
much faster than population, inflation, or insurance penetration, and faster
than non–weather-related events.”
(Mills, 2005 Science)
Is there a Weather Signal?
The Anthropogenic Climate Change IndexACCI
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Meehl et al 2004, IPCC AR4
Tem
p er
atur
e An
omal
y (o C
)
(Data from Julie Arblaster 2009)
1875 1900 1925 1950 1975 2000-0.2
0
0.2
0.4
0.6
0.8
Year
ACC
I (o
C)
• IBTraCS data without change (10 min mean), except in western North Pacific where JTWC data set is used.
• Bin all hurricanes into the Saffir-Simpson category ranges (Simpson and Riehl 1981).
• 5-y smoothed annual time series to remove ENSO type variability; p-values are calculated from the raw annual data to ensure no serial correlation.
• In addition: o Recently upgraded satellite data set and automated analysis from
Kossin (pers comm 2012),o Hurricane landfall data: our own (0.5 degree land proximity), and
from Weinkle et al (2012), ando Dynamical downscaling results of Bender et al (2008), Holland and
Suzuki-Parker (2012), and Wu and Zhao (2011).
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Tropical Cyclone Data Used
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Tropical Cyclone Response to Global Warming
0.20 0.40 0.60 0.8070
80
90
100
110
120
f(x) = 3.15586199943215 x + 89.2632680606622R² = 0.00389672217319659
ACCI (oC)
Num
ber o
f Cyc
lone
sInsignificant <3% per oC Warming
• SH Cyclones are in year season commenced
(Holland and Bruyere 2012)
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Intense Hurricane ResponseChange/oC
-30%
40%
(Holland and Webster 2007)(Elsner et al 2009)
Global
(Holland and Bruyere 2012)
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Regional Intense Hurricane Changes
Holland and Bruyere (2012)
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Summary of Available Studies
(Observed)
Changing proportion of hurricanes found by the indicated studies.
(Holland and Bruyere 2012)
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Weather Extremes Provide a Bellwether of Climate Variability
and Change
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Differing Study Results:Same Answer!
(Holland and Bruyere 2012)
Working Hypothesis: Weather extremes initially respond strongly to climate change, then reach a saturation level beyond which further climate change has little effect.
(North Atlantic)
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Note that Weather Extremes are Bounded
(Holland and Bruyere 2012)
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Character of the Observed Tropical Cyclone Changes
0 1 2 3 4 50%
20%40%60%80%
100% 65-7475-8485-9495-0405+
Category
Prop
orti
on
(Holland and Bruyere 2012)Proportion is relative to all hurricanes
• Extreme weather provides a bellwether of climate variability and change
• Global anthropogenic warming arguably commenced around 1960-1970
• Intense hurricanes have responded strongly to this warming with development of a bimodal distribution
• Intense hurricane (weather) changes may reach a saturation beyond which there is no further anthropogenic signal
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Summary