severe weather response to climate change: the expected and the unexpected

1

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.

Holland, ETH October 2012 2

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


IPCC Findings

(IPCC SREX 2012)


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:


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)


An Example: Melbourne Australia Temperatures

http://ckrao.files.wordpress.com/2011/12/spring-in-melbourne1.jpg

Maximum Temperatures




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.


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)


A Conundrum


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

Holland, ETH October 201212

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).


Tropical Cyclone Data Used


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



Intense Hurricane ResponseChange/oC

-30%

40%

(Holland and Webster 2007)(Elsner et al 2009)

Global



Regional Intense Hurricane Changes

Holland and Bruyere (2012)


Summary of Available Studies

(Observed)

Changing proportion of hurricanes found by the indicated studies.



Weather Extremes Provide a Bellwether of Climate Variability

and Change


Differing Study Results:Same Answer!


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)


Note that Weather Extremes are Bounded



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


Summary

severe weather response to climate change: the expected and the unexpected

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