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					   Changes in the incidence of climate
extremes and their links to climate change

                               Neville Nicholls
                             Monash University
                  Outline:
• Why are we interested in extremes?
• The IPCC Special Report on extremes and
  disasters.
• Observed changes in weather extremes in
  Australia.
• Are the recent heavy rains and floods in
  eastern Australia due to global warming?
• Is the warming of the past 40 years just
  reflecting rainfall trends?
             John Tyndall, 1861


    “…a slight change in its [the atmosphere’s] variable
    constituents…may have produced all the mutations
    of climate which the researches of geologists
    reveal.” Tyndall (1861)




Modern replication of Tyndall’s experiment   Carbon Tracker
      Nature, 1972


“The increase of 25% in CO2
expected by the end of the
century therefore corresponds
to an increase of 0.6˚C in world
temperature – an amount
somewhat greater than the
climatic variations of recent
centuries.”
Increased atmospheric concentration of CO2 has
   caused warming of about 0.7°C since 1970




                           Sawyer
 IPCC Special Report on “Managing the Risks of
   Extreme Events and Disasters to Advance
    Climate Change Adaptation” (or…SREX)


• 2.5 years in preparation
• 87 Coordinating Lead Authors (CLAs) and Lead
  Authors (LAs), across 9 Chapters
• Approval plenary: Kampala, Uganda, November
  2012 (Summary for Policymakers released 18
  November 2012)
• Release of complete report: 28 March 2012
SREX: key concepts and links
           SREX: Contents - 9 chapters
1: Climate change: new dimensions in disaster risk, exposure,
   vulnerability, and resilience
2: Determinants of risks: exposure and vulnerability
3: Changes in climate extremes and their impacts on the natural
   physical environment
4: Changes in impacts of climate extremes: human systems and
   ecosystems
5: Managing the risks from climate extremes at the local level
6: National systems for managing the risk from climate extremes
7: Managing the risks: international level and integration across
   scales
8: Towards a resilient and sustainable future
9: Case studies
                        SREX, Chapter 3:
• 2 Coordinating Lead Authors; 12 Lead Authors; 28 Contributing
  Authors
• Complexities: variety of extremes, definitional issues, different
  measures, scale issues
• “Moderate” extremes versus “extreme” extremes
• Tried to balance needs of policymakers for regional projections,
  with the need for scientific credibility.
• Provided regional assessments of changes in extremes of
  temperature, heavy precipitation, drought in tables and figures.
• Assessed the uncertainty of all conclusions.
• About 5000 review comments on Chapter 3 material (four rounds
  of reviews; several hundred reviewers)
• Authors respond to all review comments in writing (and comments
  & responses publically available)
                  Chapter 3: Contents
Executive Summary
3.1. Weather and Climate Events Related to Disasters
3.2. Requirements and Methods for Analyzing Changes in Extremes
3.3. Observed and Projected Changes of Weather and Climate
   Extremes
    – Temperature; Precipitation; Wind;
3.4. Observed and Projected Changes in Phenomena Related to
   Weather and Climate Extremes
    – Monsoons; El Niño – Southern Oscillation; Other Modes of Variability;
      Tropical Cyclones; Extratropical Cyclones;
3.5. Observed and Projected Impacts on the Natural Physical
   Environment:
    – Droughts; Floods; Extreme Sea Levels; Waves; Coastal Impacts (Small
       Island States); Glacier, Geomorphological and Geological Impacts;
       High-latitude Changes including Permafrost.
FAQ 3.1: Is the Climate Becoming More Extreme?
FAQ 3.2: Has Climate Change Affected Individual Extreme Events?
         Assessing uncertainty based
Step 1   on evidence and agreement




                     Step 2
Large-scale, land only, regions used for temperature &
precipitation extremes
      IPCC Special Report on Managing the Risks of Extreme Events and
           Disasters to Advance Climate Change Adaptation (SREX)




          Projected return period
(of hot day with late 20th century
        return period of 20 years)



                                       B1
                                            A1B A2
          IPCC Special Report on Managing the Risks of Extreme Events and
               Disasters to Advance Climate Change Adaptation (SREX)




            Projected return period
(of heavy daily rainfall with late 20th
  century return period of 20 years)
Comparison of projections of changes in daily
  temperature and precipitation extremes:

•“…a 1-in-20 year hottest day is likely to
become a 1-in-2 year event by the end of the
21st century in most regions…”

•“…a 1-in-20 year annual maximum daily
precipitation amount is likely to become a 1-
in-5 to 1-in-15-year event by the end of the
21st century in many regions…”
                                                     Dryness: Fig. SPM.4
Shading and stippling
to show consistency       Two dryness indices
between models




Gray shading: less than 66% model agreement on sign of change
Coloured shading: ≥ 66% model agreement on sign of change
Stippling: ≥ 90% model agreement on sign of change
   Problems projecting droughts:

• Inconsistencies between projections of the
  (many) different drought indices
• Inconsistencies between projections of even a
  single drought index, between climate models
• Geographical variations in consistency of
  projections – so it is difficult to make a
  “global” statement
• Non-climatic factors (eg land use changes)
  also important complications
                                                                   Dryness: Fig. SPM.4

Consistency between indices




Consistent projections of increased dryness for these (and other) indices in the
Mediterranean region, central Europe, southern North America, northeast Brazil, and
southern Africa
          Summary of SREX projections
• “…a 1-in-20 year hottest day is likely to become a 1-in-2 year
  event by the end of the 21st century in most regions…”
• “…a 1-in-20 year annual maximum daily precipitation amount
  is likely to become a 1-in-5 to 1-in-15-year event by the end of
  the 21st century in many regions…”
• “Average tropical cyclone maximum wind speed is likely to
  increase…It is likely that the global frequency of tropical
  cyclones will either decrease or remain essentially
  unchanged”
• “It is very likely that mean sea level rise will contribute to
  upward trends in extreme coastal high water levels in the
  future.”
• “There is low confidence in projections of small spatial-scale
  phenomena such as tornadoes and hail…”
• “There is medium confidence that there will be a reduction in the
  number of extra-tropical cyclones…there is medium confidence in
  a projected poleward shift of extra-tropical storm tracks.”
• “There is medium confidence that droughts will intensify in the
  21st century in some seasons and areas…Elsewhere there is
  overall low confidence because of inconsistent projections of
  drought changes…”
• “Projected precipitation and temperature changes imply possible
  changes in floods, although overall there is low confidence in
  projections of changes in fluvial floods…There is medium
  confidence…that projected increases in heavy rainfall would
  contribute to increases in local flooding, in some catchments or
  regions.”
• “There is low confidence in projections of changes in large-scale
  patterns of natural climate variability” [eg., El Niño]
Important points:
• Our confidence in projecting changes in extremes
  varies:
  – between extremes
  – geographically
• The expected magnitude of change varies:
  – between extremes
  – geographically
• Confidence is low for projections of many
  extremes…
• …but this does not mean there will be no change
  in these extremes!
   Observed variations in Australian
         weather extremes
• Source: http://www.bom.gov.au/climate/change/
• Indices examined:
  – Annual minimum value of daily minimum temperature
  – Annual count of days with maximum temperature >
    40°C
  – Percentage of days with maximum temperature >
    90th percentile
  – Annual maximum 1-day precipitation total
  – Annual total precipitation divided by the number of
    wet days (daily precipitation ≥ 1 mm)
• Many more indices available
   Summary of observed changes in
     Australian weather extremes:
• Temperature extremes becoming warmer (but
  still possibility of cool years such as 2011)
• Little trend in precipitation extremes


    What about 2010/11 – are the
    recent heavy rains and floods
    evidence of global warming?
East Australian September-February rainfall
   versus the Southern Oscillation Index




                                   La Niña events




  Heavy rains and floods due to record La Niña…but…
Australian average rainfall and maximum temperatures




                              Updated from Nicholls et al (1996b)
High-quality data sets now include evaporation and cloud
         IPCC SREX
http://ipcc-wg2.gov/SREX/

				
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posted:10/9/2012
language:English
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