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

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

• Neville Nicholls
• Monash University

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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?

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John Tyndall, 1861
a slight change in its the atmospheres
variable constituentsmay have produced all the
mutations of climate which the researches of
geologists reveal. Tyndall (1861)
Carbon Tracker
Modern replication of Tyndalls experiment
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Nature, 1972
The increase of 25 in CO2 expected by the end
of the century therefore corresponds to an
increase of 0.6C in world temperature an
amount somewhat greater than the climatic
variations of recent centuries.
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Increased atmospheric concentration of CO2 has
caused warming of about 0.7C since 1970
Sawyer
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IPCC Special Report on Managing the Risks of
Extreme Events and Disasters to Advance Climate
Change Adaptation (orSREX)

• 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

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SREX key concepts and links
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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

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• 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)

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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?

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Assessing uncertainty based on evidence and
agreement
Step 1
Step 2
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Large-scale, land only, regions used for
temperature precipitation extremes
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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
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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)
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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

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Dryness Fig. SPM.4
Shading and stippling to show consistency between
models
Two dryness indices
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
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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

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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
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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 increaseIt 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

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• There is medium confidence that there will be a
  reduction in the number of extra-tropical
  cyclonesthere 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
  areasElsewhere 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 floodsThere is medium
  confidencethat 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

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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!

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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 gt
  40C
• Percentage of days with maximum temperature gt
  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

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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?
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East Australian September-February rainfall
versus the Southern Oscillation Index
La Niña events
Heavy rains and floods due to record La Niñabut
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Australian average rainfall and maximum
temperatures
Updated from Nicholls et al (1996b)
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High-quality data sets now include evaporation
and cloud
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IPCC SREXhttp//ipcc-wg2.gov/SREX/