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

Neville NichollsMonash 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)

Carbon TrackerModern replication of Tyndall’s experiment

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.”

Sawyer

Increased atmospheric concentration of CO2 has caused warming of about 0.7°C since 1970

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 chapters1: Climate change: new dimensions in disaster risk, exposure,

vulnerability, and resilience2: Determinants of risks: exposure and vulnerability3: Changes in climate extremes and their impacts on the natural

physical environment4: Changes in impacts of climate extremes: human systems and

ecosystems5: Managing the risks from climate extremes at the local level6: National systems for managing the risk from climate extremes7: Managing the risks: international level and integration across

scales8: Towards a resilient and sustainable future9: 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: ContentsExecutive Summary 3.1. Weather and Climate Events Related to Disasters3.2. Requirements and Methods for Analyzing Changes in Extremes3.3. 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 on evidence and agreement Step 1

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.4Shading and stipplingto show consistencybetween 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

Two dryness indices

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 SREXhttp://ipcc-wg2.gov/SREX/