html5-img
1 / 34

Extreme weather: Climate change or climate variability?

Extreme weather: Climate change or climate variability?. Dr. Nicholas Klingaman National Centre for Atmospheric Science Walker Institute for Climate System Research. Introduction and Outline. Review of the extreme weather events of 2010-11 The Australian floods of summer 2010-11

salali
Download Presentation

Extreme weather: Climate change or climate variability?

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Extreme weather: Climate change or climate variability? Dr. Nicholas KlingamanNational Centre for Atmospheric ScienceWalker Institute for Climate System Research

  2. Introduction and Outline • 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?

  3. Extreme weather eventsin 2010-2011 Source: MODIS satellite image - December 2010: Central Queensland flooded - January 2011: Toowoomba and Brisbane flooded; also flooding in Sri Lanka, Philippines and Brazil - August 2010: Flooding in Pakistan - February 2011: Severe Cyclone Yasi strikes Queensland - Throughout 2010: Drought in Perth - July 2010: Heatwave in western and central Russia Source: telegraph.com.au Source: guardian.co.uk Source: NOAA Earth System Research Laboratory Source: U.S. Department of Defense

  4. 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

  5. The Rockhampton Floods • The wettest December on recordin 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.

  6. The Rockhampton Floods • Exceptionally heavyrain fell between Christmas and New Year’s Eve: • Rockhampton: 320 mm • Carnarvon: 265 mmon 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.

  7. The Rockhampton Floods • The proximate cause ofthe 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

  8. 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

  9. 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

  10. The cost of the Australian floods 15,000 homes destroyed 35 people killed

  11. 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?”

  12. Climate change and extreme rainfall • 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. Changes in frequency of extreme rainfallin the tropics with warming ocean temperatures Figure from Allan et al. (2010, Env. Res. Lett.)

  13. 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

  14. Brief introduction toEl Niño and La Niña • 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.

  15. 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.

  16. 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. StrongLa Niña WeakEl Niño StrongEl Niño WeakLa Niña Neutral 1974/75 2010/11 Queensland annual (May-Apr) rain (mm) Nino-4 index (degrees Celsius)

  17. 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 Differencein thenumberof1-in-30 dayrainfalleventsperseason El Niñominusneutralyears La Niña minusneutralyears

  18. 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. More heavyrainfall Climate change Strong • La Niña Heavierrainfall

  19. Severe Cyclone Yasi Yasi was“Australia’s Katrina” The track of Severe Cyclone Yasi as it passed across northern Queensland

  20. 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 riskof 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).

  21. 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 ofdayswith a tropical cyclone: 2081-2100 minus1981-2000.From Lavender et al. (2011). Temperaturechanges over1979-1999 From Thorneet al. (2010)

  22. Climate change or natural variability? • 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? Climate change More tropical cyclones Strong • La Niña Stronger tropical cyclones

  23. The Southwest Australia Drought Source: Bureau of Meteorology 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. Annual rainfall at Perth Airport, dating to 1945. The blue horizontal line isthe median annual rainfall.

  24. 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.

  25. The Southwest Australia Drought Total water stored in Western Australia dams. Source: Western Australia Water Corporation Extraction during dry season Storage in gigalitres(one million kilolitres) Recharge during wet season

  26. Climate change andthe Southern Annular Mode • Loss of ozoneand 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).

  27. Impacts of CO2 doubling Summer Autumn Winter Spring Change in annual-total rainfall fromHiGEM 2xCO2 minus HiGEM control

  28. 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.)

  29. 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 surface temperaturesfrom normal July conditions Departures of July 2010 precipitationfrom normal July conditions

  30. The Russian Heatwave Departures ofJuly 2010 sea-level pressurevalues fromnormal conditions The heat and drought in Russia was associated witha strong blocking pattern in the atmosphere, withsubstantial meanders in the jet stream directing weather systemsaway from Russia.

  31. Climate change or natural variability? • Climate changeis expected toconsiderablyincrease the risk of heatwavesin 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 simulationsfrom 22 climate models.

  32. 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 numberand strengthof 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.

  33. 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!

  34. 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

More Related