© University of Reading 2012 www.reading.ac.uk

Extreme weather: Climate change or climate variability?

Dr. Nicholas KlingamanNational Centre for Atmospheric ScienceWalker Institute for Climate System Research

• Review of the extreme weather events of 2010-11

• The Australian floods of summer 2010-11• “Is it climate change?”• La Nina and tropical flooding• Severe Tropical Cyclone Yasi• Drought in Southwest Australia• The Russian heatwave of summer 2010• Conclusions – Should we blame ourselves?

Introduction and Outline

- February 2011: Severe Cyclone Yasi strikes Queensland

- January 2011: Toowoomba and Brisbane flooded;

also flooding in Sri Lanka, Philippines and Brazil

- December 2010: Central Queensland flooded

Extreme weather eventsin 2010-2011

- Throughout 2010: Drought in Perth

- August 2010: Flooding in Pakistan

- July 2010: Heatwave in western and central Russia

Source: U.S. Department of DefenseSource: NOAA Earth System Research Laboratory

Source: telegraph.com.au

Source: guardian.co.uk

Source: MODIS satellite image

Brief introduction toAustralian climate

• Australia’s coasts receivethe vast majority of the rainfall.

• About 70% of Australia receivesless than 500 mm of rainfallper year (about half ofSE England’s average rainfall).

• The northern third of Australiareceives nearly all of its rainfall in summer (December-February).

• The southern third of Australia receives most of its rainfall inwinter (June-August).

Source: bigthink.com

The Rockhampton Floods• The wettest December on record

in Queensland; the second-wetteston record in Australia (since 1900).

• Much of Queensland receivedmore than twice its average rainfall.

• The wet December followed thewettest spring on record in Australia.

The Rockhampton Floods• Exceptionally heavy

rain fell between Christmas and New Year’s Eve:

• Rockhampton: 320 mm• Carnarvon: 265 mm

on 27 December alone

• Roughly five times the average rainfall for December

• Daily rainfall records fell along the Carnarvon Hills to the west of Rockhampton

• Thousands of squarekilometres flooded.

The Rockhampton Floods• The proximate cause of

the heavy rainfall wasthe combination of

• High pressure to the south, in the Tasman Sea

• Low pressure to the north, along the Queensland coast

• The combined circulationaround these systems directed warm, moist oceanair onshore, which subsequently rose over the Carnarvon Hills, producing heavy rainfall

The Brisbane Floods• Southeastern Queensland received

heavy rain 6-12 January 2011• Brisbane: 267 mm• Toowoomba: 345 mm

• Flash flooding struck Toowoomba on 10 January

• Similar onshore wind pattern to Rockhampton floods

The Brisbane Floods• Brisbane City gauge

reached a height of 4.46 metres, well below the record highest floods.

• The Wivenhoe Dam was constructed in the wake of the 1974 floods (5.45 metres) to protect the city.

• Preliminary results: Without the Wivenhoe Dam, the river level at the City gauge would have been 6.5 metres (Neville Nichols, Monash University)

2011

The cost of the Australian floods

15,000 homes destroyed

35 people killed

Climate change and extremes• In the wake of the Queensland floods, many asked:

“Is it climate change?” … or:

“Would the Queensland floods have occurred if humans were not warming the climate through greenhouse-gas emissions?”

• Climate change will affect the overall number and strength of extreme weather events.

• Two slightly easier and much more useful questions:

“Will floods in Queensland become more frequent?”“Will floods in Queensland become more intense?”

Climate change and extreme rainfall

Changes in frequency of extreme rainfallin the tropics with warming ocean temperaturesFigure from Allan et al. (2010, Env. Res. Lett.)

• For the tropics as a whole,the frequency of extremerainfall is expected to increase with warmingtemperatures.

• Clausius-Clapeyron: the atmosphere has a greater capacity for water vapour at higher temperatures.

• This does not mean that global warming will be every rainfall event stronger, or that total rainfall will increase everywhere.

Climate change and Queensland extreme rainfall

• For Queensland,doubling CO2in a climate modelincreases thefrequency of 100 mm/day rainfallby 50%:

• Present-day:1 in 670 days

• Double CO2:1 in 402 days

• Doubling CO2 alsoalso increases theintensity of a 1-in-200day event by 20%:

• Present-day: 54 mm• Double CO2: 65 mm

Frequency of different amounts of rainfall in Queenslandduring summer, for present-day and 2xCO2 climates

• La Niña and El Niño are naturally occurring phenomena, in which ocean temperatures in the equatorial Pacific cool and warm, respectively.

• Events often develop in June-September, peak in December-February, then decay in March-May.

• La Niña and El Niño are episodic (irregular). El Niño does not necessary follow La Niña; neutral conditions can prevail for years.

• The strength and position of warm ocean temperatures shifts rainfall patterns around the world.

Brief introduction toEl Niño and La Niña

Brief introduction toEl Niño and La Niña

El Niño

La Niña

Departures of ocean temperatures in the central equatorial Pacific from average conditions

(Source: KNMI Climate Explorer from UK Met Office data)

There are insufficient reliable data to determine whether El Niño and La Niña are changing with global warming.

Historical relationships betweenLa Niña and Australian rainfall

• On average, El Niño and La Niñaare responsiblefor approximately25% of theyear-to-yearvariations inQueensland rainfall.

• Strong La Niñaevents result inlarge floods inQueensland, butstronger El Niñoevents do not resultin strongerdroughts.

Que

ensl

and

annu

al (M

ay-A

pr) r

ain

(mm

)

Nino-4 index (degrees Celsius)

WeakLa Niña

WeakEl Niño

StrongEl NiñoNeutral

StrongLa Niña

1974/75

2010/11

Historical relationships betweenLa Niña and heavy rainfall

• La Niña increases by 20-70% the risk of heavy rainfall in Queensland• El Niño reduces by 10-40% the risk of heavy rainfall in Queensland

La Niñaminusneutralyears

El Niñominusneutralyears

Differencein the

numberof

1-in-30 dayrainfallevents

perseason

Climate change or natural variability?

• Scientists expect warming temperatures to increase the frequency and intensity of extreme rainfall, particularly in the tropics.

• There is a strong historical link between La Niña and strong monsoon seasons in Australia, including with the frequency of extreme rainfall.

• There is no robust evidence that global warming has influenced the frequency or intensity of La Niña; the 2010-11 event was strong, but not outside the range of past events.

Climate change

StrongLa Niña

Moreheavyrainfall

Heavierrainfall

Severe Cyclone Yasi

The track of Severe Cyclone Yasi as it passed across northern Queensland

Yasi was“Australia’s Katrina”

Historical relationships betweenLa Niña and tropical cyclones

Observed tropical-cyclone tracks during the sevenEl Niño and La Niña events from 1979-2009.

• Compared to El Niño, La Niña doubles the risk of a tropical cyclone striking eastern Australia (Callaghan and Power, 2010)

• All years in which more than one tropical cyclone has struck easternAustralia have been La Niña years (Callaghan and Power, 2010).

Climate change andtropical cyclones

• In a warmer world, we expect to see fewer tropical cyclones.

• The decrease may not be evenly spread across the globe; some regions may have more cyclones.

• The intensity of tropical cyclones, particularly the strongest ones, is expected to increase.

Estimates from threemodels of the changein the number of days

with a tropical cyclone: 2081-2100 minus

1981-2000.From Lavender et al.

(2011).

From Thorneet al. (2010)

Temperaturechanges over1979-1999

Climate change or natural variability?

Climate change

StrongLa Niña

More tropical cyclones

• Climate change is expected to reduce the number, but increase the intensity of tropical cyclones in the Southwest Pacific.

• La Niña increases the number of landfalling tropical cyclones in eastern Australia, but has no effect on their overall intensity.

• Was Yasi “enhanced” by global warming? Would Yasi have even formed in a warmer world? In an El Niño year, would Yasi have simply have moved out to sea?

Stronger tropical cyclones

The Southwest Australia Drought

Rainfall in Southwest Western Australia for January-October; the red bars are the five driest years; the black line is the 15-year moving average.

Source: Bureau of Meteorology

Annual rainfall at Perth Airport, dating to 1945. The blue horizontal line isthe median annual rainfall.

The Southwest Australia Drought

• Western Australia producesthe most wheat of any statein Australia.

• The 2010 drought likelyreduced wheat yields byone-third, equivalent tonearly AU$1 billion(£650 million).

• Heavy rains in the east ofAustralia in September-November damaged wheat crops as they were being harvested.

The Southwest Australia Drought

Sto

rage

in g

igal

itres

(one

mill

ion

kilo

litre

s)Extraction during dry

season

Rechargeduring wet

season

Total water stored in Western Australia dams.

Source: Western Australia Water Corporation

Climate change andthe Southern Annular

Mode• Loss of ozone

and increasinggreenhousegases have hadthe largestimpact on theSouthern AnnularMode to date.

• The tensionbetween therecovery of theozone hole andincreasinggreenhouse gases is an openissue. Simulated changes in surface pressure associated with observed

changes (1958-1999) in each driver. Figure from Arblaster et al. (2006).

Impacts of CO2 doubling

Change in annual-total rainfall fromHiGEM 2xCO2 minus HiGEM control

Summer Autumn

SpringWinter

Climate change or natural variability?

• The ozone hole and greenhouse-gas emissions have each contributed to the positive trend in the Southern Annular Mode.

• There is little evidence for natural, decadal variability in the Southern Annular Mode, but records are likely not long enough to robustly detect such variations.

• Ozone loss and greenhouse-gas emissions are the most likely causes of the decline in rainfall in Southwest Australia.

Greenhouse gas

emissions

Antarctic ozone

hole

Drought in SW

Australia

Natural variations

(solar, etc.)

?

Departures of July 2010 surface temperaturesfrom normal July conditions

The Russian Heatwave• Intense heat and drought

throughout western Russia resulted in tens of thousands of deaths.

• Highest temperature ever recorded in Russia: 44.0°C (111.2°F)

• Grain harvest ruined, at a cost of $15 billion (£9.4 billion) in GDP

• Russia banned grain exports, leading to further worldwide increases in grain prices. Departures of July 2010 precipitation

from normal July conditions

The Russian Heatwave

The heat and drought in Russia was associated witha strong blocking pattern in the atmosphere, with

substantial meanders in the jet stream directing weather systems away from Russia.

Departures ofJuly 2010 sea-level pressure values fromnormal conditions

Climate change or natural variability?

• Climate changeis expected toconsiderablyincrease the risk of heatwaves in many parts of the world,including Europeand Russia.

• The 2010 heatwave was likely the result of natural variations that were intensified by man-made climate change (Dole et al., 2011).

Frequency of western Russia July temperatureextremes, based on climate-change simulations

from 22 climate models.

Should we blame ourselves?• Humans are definitely warming the climate through

emissions of greenhouse gases.• A warming climate is affecting and will affect

weather patterns, especially the number and strength of extreme weather events.

• The effects of climate change are being seen and will be seen in the overall behaviour of extreme events.

• Natural variations, like La Niña, still have an important role in determining when and where extreme weather will occur.

• For individual events, trying to separate natural variations from climate change is not easy and (in my opinion) not particularly useful for adapting to climate change.

Shameless self-promotion• After the violent eruption of Mount

Tambora (Indonesia) in April 1815, 1816 became known as “The Year Without a Summer”.

• One of the four strongest volcanic eruptions of the last 10,000 years. A powerful example of natural climate change.

• Covers the eruption, how the volcanic ash cloud affected global weather and climate, and the subsequent impacts on agriculture, migration and public health.

• Published late February 2013, but available for pre-order on amazon.co.uk!

For further information• E-mail: n.p.klingaman@reading.ac.uk• Web: http://www.met.rdg.ac.uk/~ss901165• Twitter: @nick_klingaman

To find out more about Reading’s climate research:• Walker Institute:

http://www.walker-institute.ac.uk• NCAS-Climate: http://climate.ncas.ac.uk

More information on climate change research:• Royal Meteorological Society:

http://www.rmets.org• Intergov. Panel on Climate Change:

http://www.ipcc.ch