Hanlon ECI 2007

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Oxford University

Climate Change and Extreme WeatherEvents

Helen Hanlon

Department of Physics, University of Oxford

[email protected]

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Why we need a new perspective on the climatechange issue

There are three major stakeholders in this issue: Fossil fuel producers.

Fossil fuel consumers.

Everyone at risk from climate change (the impacted).

The mantra climate change affects us all is

misleading: it affects some much more than others.

Impacts are increasingly clear and will likely lead tomeaningful action to reduce emissions by the 2020s.

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Khadijateri cave paintings

Myth: Climate has always varied, so the presenttrend is nothing to worry about

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Fact: we cannot explain the past century withoutboth human and natural influence on climate

Colours: Simulations with human and natural influences

Observations

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Fact: we cannot explain the past century withoutboth human and natural influence on climate

Colours: Simulations with natural influences alone

Observations

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Regional Temperatures for the IPCC AR4 Models

Daithi Stone, 2007

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Myth: not all scientists agree that this warmingwill continue if GHG levels continue to rise

Pat Michaels(2000, 2004)

Climate response tothe IS92a scenarioof future emissions,predicted by 2001IPCC models and byPatrick Michaels, aprominent critic ofthe IPCC

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Myth: the most significant impacts of climatechange only affect people living in photogenic

places

Exotic island under water due toSea-level rise

Melting of polar ice caps threateningthe habitat of polar bears and otherpolar wildlife.

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Surface temperaturedepartures fromnormal in earlyAugust 2003, from

NASAs ModerateResolution ImagingSpectrometer,courtesy of RetoStckli, ETHZ

Fact: the most significant impacts of climatechange are changing risks of extreme weather

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Myth: climate change was to blame forHurricane Katrina

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Myth: climate change was notto blame forHurricane Katrina

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Myth: scientists have no idea whether climatechange was to blame for Hurricane Katrina

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Fact: we can establish a causal link betweenindividual weather events and climate change

The drivers of climate change (greenhouse gases,

volcanic eruptions) affect weather in the way thatthe loading on a dice helps the dice to come up six.

Climate is what you expect,

weather is what you get

(Lorentz, 1982)

Updated for the 21st century

Climate is what you affect, weather is what gets you

(Myles Allen 2003)

But we cannot roll the weather dice many times to

work out how the loading is changing, so we have to

use computer simulation.

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A more challenging example: flood risk in theUnited Kingdom

River Trent, Nottingham, Autumn 2000

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South Oxford on January 5th, 2003

Photo:Da

veMitchell

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West Oxford on July, 2007

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It has happened before: Shillingford historicflood levels

2003

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Autumn 2000 floods in the UK

Sep-Nov 2000 was wettest Autumn in England &

Wales since records began in 1766, with almostdouble (196%) the 1961-1990 average seasonalprecipitation.

Nationwide impact:1.3bn of insured loss.

Over 10,000 properties

flooded.

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Standard climate models may be good enoughfor heat-waves, but not for precipitation

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The climateprediction.net seasonal attributionexperiment (Pall et al, 2007)

Aim: to quantify the role of increasedgreenhouse gases in precipitationresponsible for 2000 floods.

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Autumn 2000as observed(ERA-40reanalysis)

and in oneof the wettermembers ofour ensemble.

Ch i fl d i k i th U it d Ki d d t

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Changing flood risk in the United Kingdom due togreenhouse gas increase 1900-2000

Wh ti t t l h i i

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Why action to control greenhouse gas emissionsmay be coming sooner than you expect

We estimate that there is a better than 9 in 10 chancethat past human influence has more than doubledthe risk of a heat-wave equal or greater than thesummer of 2003 (Stott et al, 2004).

Soon (not yet) we may be able to do the same for

floods in Oxford, droughts in Libya and hurricanes in

Louisiana.

Plaintiffs ... must show that, more probably than

not, their individual injuries were caused by the risk

factor in question, as opposed to any other cause.This has sometimes been translated to a

requirement of a relative risk of at least two.

(Grossman, 2003)

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The worlds largest climate modelling facility:www.climateprediction.net

~260,000 volunteers, 170 countries

Si l ti th li t th t i ht h b

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Simulating the climate that might have been onyour desktop: http://attribution.cpdn.org

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Questions?

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M th b d t t h b

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Myth: observed temperature changes can beexplained by solar variability

Hanlon ECI 2007

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