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?
Step 1
Low
confidence
Assess
confidence
level
Medium
confidence
Direction of
change only
Virtually
certain (99100%)
Very likely
(90-100%)
Assessing uncertainty based
on evidence and agreement
High
confidence
Likelihood
assessment
Likely (66100%)
Step 2
More likely
than not
(50-100%)
About as
likely as not
(33-66%)
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 1in-5 to 1-in-15-year event by the end of the
21st century in many regions…”
Shading and stippling
to show consistency
between models
Dryness: Fig. SPM.4
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
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/