Climate Futures for the
Southeast Australian Coast
Supporting information for the National Climate
Change Adaptation Research Facility (NCCARF)
Coastal Settlements projects:
What would a climate-adapted settlement
look like?
South East coastal adaptation (SECA) project
Dave Griggs, Will Steffen & Tahl Kestin
MSI Report 12/04
May 2012
www.monash.edu/research/sustainability-institute
Monash Sustainability Institute
Building 74, Clayton Campus
Monash University, Victoria 3800, Australia
T: +61 3 9905 9323
E: enquiries@msi.monash.edu
W: www.monash.edu/research/sustainability-institute/
Prepared by Dave Griggs & Tahl Kestin (Monash Sustainability Institute, Monash
University) and Will Steffen (The ANU Climate Change Institute, Australian National
University)
MSI Report 12/4, May 2012
ISBN: 978-0-9870821-2-1
Cover image: Steb Fisher
ACKNOWLEDGEMENTS
This work was carried out with financial support from the Australian Government (Department of Climate Change and Energy Efficiency) and the
National Climate Change Adaptation Research Facility. The views expressed herein are not necessarily the views of the Commonwealth, and the
Commonwealth does not accept responsibility for any information or advice contained herein.
DISCLAIMER FOR CSIRO FIGURES
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appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise directly or
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Table of Contents
INTRODUCTION1
SURFACE AIR TEMPERATURE
Observed trends – Average surface air temperature
Observed trends – Hot days
Observed trends – Cold nights
Future trends – Average surface air temperature
Future trends – Hot days
3
3
4
5
6
7
RAINFALL8
Observed trends – Annual rainfall totals
Observed trends – Extreme rainfall
Observed trends – Dry periods
Future trends – Total rainfall
Future trends – Extreme rainfall
Future trends – Dry periods
SEA SURFACE TEMPERATURES
Observed trends – Sea surface temperatures
Future trends – Sea surface temperatures
SEA LEVEL
Observed trends – Sea level
Future trends – Sea level
COASTAL INUNDATION AND EROSION
8
9
9
10
11
12
13
13
14
15
15
16
18
BUSHFIRES19
OTHER CLIMATE RELATED RISKS
20
SOURCE MATERIAL AND BACKGROUND READING
21
Introduction
This report on climate futures is designed to serve two NCCARF projects –
(i) What would a climate-adapted settlement look like?, which focuses on two communities
on the Gippsland coast, and (ii) the South East Coastal Adaptation (SECA) Project, which is
focussed primarily on the south coast of New South Wales.
In the analyses that follow, we have included both study areas
together (referred to as the southeast Australian coast) but noted
differences where they occur, differentiating the study areas as
“the Gippsland coast” and “the NSW south coast”.
The section is structured around climatic variables of importance
for adaptation – air temperature, rainfall (and wetness/dryness),
sea surface temperature, sea level, and some aspects of
storminess, such as thunderstorms and hailstorms. Where
appropriate and where information is available, we consider
changes in both average and extreme values of the variable.
Extremes, such as heat waves and heavy rainfall events, are
especially important to inform risk analysis.
For each variable we have included both the observed change in
the variable up to the present and projected changes for the
future. For observed change, we have focussed on the
1970–2011 trends (compared to the longer-term averages in the
variable, which, for most Australian records, go back to 1900 or
1910). The last four decades encompass most of the observed
trends that have been influenced by anthropogenic climate
change.
The projections of future climate trends are based on a set of
trajectories of future greenhouse gas emissions known as the
SRES scenarios (as they were developed in the IPCC (2000)
Special Report on Emission Scenarios; Figure 1). SRES provides
a range of emission trajectories based on different but equally
sound social, technological and policy futures.
For projections of future trends, we have focussed on two time
slices – 2030 and 2070. Although 2030 will often be the most
relevant and useful timeframe for adaptation strategies, decisions
on long-lived infrastructure development may also benefit from
consideration of projections to 2070.
Unless otherwise specified, the projections will have the following
characteristics: (i) the baseline is the average of the variable
during the 1980–1999 period and is referred to as the “1990
baseline”; (ii) the 2030 projections are an average of the
2020–2039 period; (iii) the 2070 projections are an average of the
2060–2079 period; (iv) three projections are given for each time
period, representing low, medium and high emission scenarios;
(v) a number of climate models are used for each projection (for a
given time period and emission scenario) with the results
presented as percentiles (10th, 50th and 90th). More details on
the projection methodology and presentation are given in the
appropriate reference.
We also include some climate-related risks that are very
important for adaptation but that depend on combinations or
aggregations of climatic variables rather than on changes in
single variables. Risks associated with coastal flooding and
bushfires are good examples.
Our analyses are based on published, peer-reviewed material so
far as possible. Observational data are sourced primarily from the
Australian Bureau of Meteorology. Many of the projections for the
future are taken from the Climate Change in Australia reports
prepared by CSIRO and the Australian Bureau of Meteorology. A
list of references and other supporting and background material
is given at the end of the report.
FIGURE 1: SRES scenarios for future greenhouse gas emissions
(coloured lines). Results presented in this report use the B1 scenario to
represent low future emissions; the A1B scenario to represent medium
future emissions; and either the A2 or A1FI scenarios to represent high
future emissions. (Source: IPCC (2007a), Figure 3.1.)
1
There is often a tension between the desire for climate futures
information at fine spatial and temporal scales and the reliability
of the projections at the desired scales.
This tension is manifest in several features of this section:
ff There is more confidence in projections of temperature
change than of rainfall change. Temperature is more
directly related to the change in energy balance at the
Earth’s surface, so we know the direction of change
(increasing temperature) with much more confidence and
can often identify well-defined ranges in the magnitude of
change. Rainfall is a much more complex variable than
temperature, so in many cases we don’t know the
direction of rainfall change with a high degree of
confidence, and the ranges in the projected changes in the
magnitude of rainfall are often higher than the
corresponding ranges for projected temperature changes.
We have attempted to carefully describe the uncertainties
around projected changes in rainfall at appropriate points
in the section.
ff In general, we have more confidence in projected changes
in average values than we do in changes in extremes.
ff Projections of future change in climatic variables are only
meaningful at temporal scales of two decades or more.
Shorter timescales are increasingly dominated by modes
of natural variability than by the longer term underlying
trends.
Finally, this section is based on the most up-to-date science
available as of May 2012. However, climate science is continually
improving so the analyses in this section should be re-visited at
regular intervals as the science improves. In particular, the Fifth
Assessment Report (AR5) of the Intergovernmental Panel on
Climate Change (IPCC) is due to be published in 2013 (Working
Group 1 – basic science) and 2014 (impacts and adaptation).
Furthermore, updated climate scenarios for Australia, based on
the climate model outputs assessed in the AR5, will be released
on the same timeframe.
ff We can say more about projected change at large spatial
scales than at local or small regional scales. Thus, for
many of the projections below, we treat both study areas
together as a single spatial unit. In some cases, we can
differentiate between the two study areas. In no cases can
we carry out the analyses at any finer spatial scale than a
study area as a whole. For extremes of temperature,
rainfall and dryness, the analyses are reported only at the
scale of southern Australia as a whole.
2
Surface Air Temperature
Observed Trends – Average Surface Air Temperature
a) Maximum Temperature
b) Minimum Temperature
c) Mean Temperature
FIGURE 2: Trends in temperatures over Australia over the period
1970 to 2011, plotted in degrees Celsius per decade: (a) maximum
temperature; (b) minimum temperature; and (c) mean temperature
(which is the average of the daily maximum and minimum
temperatures). (Source: Bureau of Meteorology: http://www.bom.gov.
au/climate/change/acorn-sat/.)
There has been a warming trend of between 0.15 and 0.3°C
every ten years in maximum temperature over the last 40 years
for the southeast Australian coast, with a warming of 0.2 to 0.3°C
every ten years for the Gippsland coast study area and 0.15 to
0.3°C every ten years over the NSW south coast (Figure 2a).
Trends in maximum temperature tend to be slightly lower near the
coast in the NSW south coast area compared to inland due to
the cooling effect of the ocean, e.g., sea breezes.
There has been an observed increase in mean (average of the
daily maximum and minimum temperature) temperature of 0.1 to
0.3°C every 10 years over the last 40 years for the southeast
Australian coast (Figure 2c), with the majority of the area warming
between 0.1 to 0.2°C every 10 years.
There has been a warming trend of between 0.1 and 0.3°C every
ten years in minimum temperature over the last 40 years for the
southeast Australian coast (Figure 2b), with a warming of 0.1 to
0.2°C for the Gippsland coast study area and 0.1 to 0.3°C over
the NSW south coast study area.
3
Observed Trends – Hot Days
a) Number of Hot Days
b) Number of Hot Days - Australian Average
c) Temperature of the Hottest Day
d) Warm Spell Duration
As can be seen from Figure 3a most sites in Gippsland show an
increase in the number of hot days (above 35°C) of 2.5 days
every ten years, whereas in the NSW south coast area there is
little or no discernible trend. Inland there has been a larger
increase in the number of hot and very hot (greater than 40°C,
not shown) days in southeast Australia. However, as can be seen
from Figure 3b for the whole of Australia, any trend is
superimposed on a high degree of year to year variability.
There have been increases in the maximum temperature of the
hottest day of between 0.2 and 0.8°C every 10 years over the
last 40 years for the southeast Australia coast (Figure 3c), with
the exception of a couple of stations which show little change or
a slight decrease . Although there is limited data, the few
observations from the southeast Australia coast indicate that
there have also been increases in the duration of warm spells of
about 2.5–5 days every 10 years (Figure 3d).
FIGURE 3: Trends in several indicators of hot days: (a) trends in the
number of days over 35°C (in days per decade) over the period 1970
to 2011; (b) annual number of days over 35°C, averaged over Australia;
(c) trends in the temperature of the hottest day recorded each year (in
degrees Celsius per century) over the period 1970 to 2011; and (d)
trends over the period 1970–2011 in the number of days each year (in
days per decade) that occur during warm spells – that is, during a
period of at least 4 consecutive days when daily maximum
temperature is greater than a threshold based on the 90th percentile
for the period 1961–1990. (Source: Bureau of Meteorology: http://
www.bom.gov.au/climate/change/acorn-sat/.)
4
Observed Trends – Cold Nights
a) Number of Cold Nights
b) Number of Cold Nights - Australian Average
c) Temperature of the Coldest Night
d) Number of Frost Nights
The number of cold nights (minimum less than 5°C) has generally
decreased by 2.5-5 days every ten years in the two study areas
(Figure 4a). A similar trend is observed in the number of frost
nights (Figure 4d), with a decline of 2.5 days every 10 years in the
Gippsland coast. There is little data for the NSW south coast, as
frosts are uncommon in this area, however large declines in the
number of frost nights are observed further inland. As can be
seen from Figure 4b showing data from Australia as a whole this
trend is superimposed on a high degree of year to year variability.
FIGURE 4: Trends in several indicators of cold nights: (a) trends in
the number of nights less than 5°C (in days per decade) over the
period 1970 to 2011; (b) annual number of nights colder than 5°C,
averaged over Australia; (c) trends in the temperature of the coldest
night recorded each year (in degrees Celsius per century) over the
period 1970 to 2011; and (d) trends in the number of frost nights
(temperature less than 0°C) over the period 1970–2011 (in days per
decade). (Source: Bureau of Meteorology: http://www.bom.gov.au/
climate/change/acorn-sat/.)
As can be seen from Figure 4c there have been increases in the
temperature of the coldest night recorded each year of between
0.2 and 0.4°C every 10 years over the last 40 years over the
southeast Australian coast.
5
Future Trends – Average Surface Air Temperature
a) 2030
b) 2070
By combining the low emissions scenario with the 10th percentile
and the high emissions scenario with the 90th percentile a range
of temperature increase for the southeast Australian coast by
2030 can be given as 0.3 to 1.5°C compared to a 1990 baseline
(Figure 5a).
By combining the low emissions scenario with the 10th percentile
and the high emissions scenario with the 90th percentile a range
of temperature increase for the southeast Australian coast by
2070 (Figure 5b) can be given as 1 to 4°C, compared to the
1990 baseline (1980–1999 average). In this case the projected
temperature increases are lower for the Gippsland coast study
area (1 to 3°C) compared to the NSW south coast (1.5 to 4°C).
FIGURE 5: Projected changes in annual average surface air
temperature: (a) 2030 and (b) 2070 relative to the 1990 baseline. The
50th percentile (the mid-point of the spread of model results) provides
a best estimate result. The 10th and 90th percentiles (lowest 10% and
highest 10% of the spread of model results) provide a range of
uncertainty. Emissions scenarios are from the IPCC Special Report on
Emission Scenarios: “Low emissions” – B1 scenario; “medium
emissions” – A1B scenario; and “high emissions” – A1FI scenario.
(Source: CSIRO & Bureau of Meteorology (2007), Climate Change in
Australia: http://www.climatechangeinaustralia.gov.au.)
6
Future Trends – Hot Days
Return Period
Legend
Year
Figure 6 shows the change in frequency of the hottest day that
now occurs on average once in 20 years over southern Australia.
Results are shown for three IPCC emissions scenarios (B1, A1B
and A2). Note that the time periods for these projections are
different from those given earlier, namely the twenty year periods
centred on 2055 and 2090. The figure shows that a 1 in 20 year
hottest day today is projected to become about a 1 in 3 to 1 in 5
year occurrence by 2055 and a 1 in 3.5 year to almost an annual
occurrence by 2090.
FIGURE 6: Projected changes in the return period for the
maximum daily temperature that was exceeded on average once
during a 20-year period in the late 20th century (1981–2000),
averaged over southern Australia and New Zealand.
A decrease in return period implies more frequent extreme
temperature events (i.e., less time between events on average). The
box plots show results for two time horizons: 2055 (2046–2065
average) and 2090 (2081–2100 average), and for three different SRES
emissions scenarios: B1 (blue, low emissions), A1B (green, medium
emissions), and A2 (red, high emissions). Results are based on 12
global climate models (GCMs) contributing to the third phase of the
Coupled Model Intercomparison Project (CMIP3). The level of
agreement among the models is indicated by the size of the coloured
boxes and the length of the whiskers. (Source: Adapted extract of
Region 26 – Southern Australia/New Zealand from Figure SPM.4A of
IPCC (2012) Special Report on Managing the Risks of Extreme Events
and Disasters to Advance Climate Change Adaptation, http://
ipcc-wg2.gov/SREX/.)
7
Rainfall
Observed Trends – Annual Rainfall Totals
a) Annual Trends
b) Seasonal Trends
SUMMER
AUTUMN
WINTER
SPRING
mm/10 years
c) Number of Wet Days
FIGURE 7: Trends in total rainfall: (a) annual trends in total rainfall (in
mm per decade) from 1970 to 2011; (b) seasonal trends in total rainfall
(in mm per decade) from 1970 to 2011; and (c) the number of wet days
(days with more than 1 mm of rainfall). (Source: Bureau of Meteorology,
http://www.bom.gov.au/climate/change/)
Over the past 40 years there has been a strong drying trend
along the southeast Australia coast, with a decline of 30–50 mm
per decade in the Gippsland coast area, and 40–60 mm per
decade in the NSW south coast (Figure 7a). Mirroring the
decrease in total rainfall over the past 40 years, the number of
wet days has also declined in the southeast Australia coast area
(Figure 7c).
The observed trends in rainfall show pronounced seasonality
(Figure 7b), particularly for the NSW south coast. There the drying
trend is especially strong in autumn, and somewhat less
pronounced but still clear in summer and spring. For the
Gippsland coast the drying trend is more evenly distributed
throughout the year but slightly more pronounced in autumn.
8
Observed Trends – Extreme Rainfall
a) Number of Heavy Rain Days
b) Annual Highest 1-Day Total
Over the past 40 years, extreme rainfall has declined in line with
the decline in total rainfall, as shown by (i) the number of days
with heavy rainfall (Figure 8a), and (ii) the highest daily
precipitation each year (Figure 8b).
FIGURE 8: Trends in indicators of extreme rainfall: (a) trends in the
number of days with heavy rainfall (i.e., rainfall greater than 10 mm per
day); and (b) trends in the highest daily rainfall recorded each year.
(Source: Bureau of Meteorology, http://www.bom.gov.au/climate/
change/.)
Both of these indicators have decreased over the 40-year period,
with the reductions somewhat greater for the NSW south coast
than for the Gippsland coast.
Observed Trends – Dry Periods
FIGURE 9: Trends (in days per century) in the maximum number
of consecutive days with daily precipitation less than 1mm each
year over the period 1970 to 2011. (Source: Bureau of Meteorology,
http://www.bom.gov.au/climate/change/.)
While annual total rainfall has declined over southeast Australia,
the number of consecutive dry days (Figure 9) has slightly
decreased along the coast (shorter periods of dry weather), but
has increased inland (longer periods of dry weather).
9
Future Trends – Total Rainfall
a) 2030
b) 2070
The range of uncertainty for projected rainfall change in 2030
across Australia is very large (Figure 10a). The Gippsland coast
ranges from no change in rainfall to a decline of up to 10%. The
NSW south coast ranges from an increase of 5% to a decline of
10%.
The range of projected rainfall changes in 2070 is high (Figure
10b), indicating a high level of uncertainty in both the future
direction and magnitude of rainfall trends. For the Gippsland
coast, trends in projected rainfall vary from no change to a
decline of up to 40%. For the NSW south coast, trends in
projected rainfall vary from an increase of 10% to a decline of up
to 40%.
FIGURE 10: Projected changes in annual rainfall in: (a) 2030 and
(b) 2070 relative to the 1990 baseline. The 50th percentile (the
mid-point of the spread of model results) provides a best estimate
result. The 10th and 90th percentiles (lowest 10% and highest 10% of
the spread of model results) provide a range of uncertainty. Emissions
scenarios are from the IPCC Special Report on Emission Scenarios:
“Low emissions” – B1 scenario; “medium emissions” – A1B scenario;
and “high emissions” – A1FI scenario. (Source: CSIRO & Bureau of
Meteorology (2007), Climate Change in Australia: http://www.
climatechangeinaustralia.gov.au.)
10
Future Trends – Extreme Rainfall
Return Period
Legend
Year
Figure 11 shows the change in frequency of very heavy daily
rainfall events that now occur on average once in 20 years over
southern Australia. Results are shown for three IPCC SRES
emissions scenarios (B1, A1B and A2). Note that the time
periods for these projections are different from those above,
namely the twenty year periods centred on 2055 and 2090.
These results indicate a modest increase in extreme rainfall
events over the southern Australian region. Results suggest that
daily rainfall events that now occur once every 20 years will occur
once every 15–17 years by 2055 and once every 9–17 years by
2090.
FIGURE 11: Projected changes in the return period for daily
rainfall that was exceeded on average once during a 20-year
period in the late 20th century (1981–2000), averaged over
southern Australia and New Zealand.
A decrease in return period implies more frequent extreme rainfall
events (i.e., less time between events on average). The box plots show
results for two time horizons: 2055 (2046–2065 average) and 2090
(2081–2100 average), and for three different SRES emissions
scenarios: B1 (blue, low emissions), A1B (green, medium emissions),
and A2 (red, high emissions). Results are based on 14 GCMs
contributing to the CMIP3. The level of agreement among the models
is indicated by the size of the coloured boxes and the length of the
whiskers. (Source: Adapted extract of Region 26 – Southern Australia/
New Zealand from Figure SPM.4B of IPCC (2012) Special Report on
Managing the Risks of Extreme Events and Disasters to Advance
Climate Change Adaptation, http://ipcc-wg2.gov/SREX/)
11
Future Trends – Dry Periods
Projections (Figure 12) indicate an increase in the number of
consecutive dry days in southeastern Australia by 2090
(2081–2100 average). However, projected decreases of soil
moisture are less consistent for the same region, suggesting low
confidence in future drought projections.
FIGURE 12: Projected annual changes in dryness assessed from
two indices: Change in annual maximum number of consecutive dry
days (days with rainfall less than 1 mm) (left); and changes in soil
moisture (right). Increased dryness is indicated with yellow to red
colours; decreased dryness with green to blue. The figures show
changes for two time horizons: 2055 (2046–2065) and 2090
(2081–2100), as compared to late 20th-century values (1980–1999),
based on the SRES A2 emissions scenarios (high emissions). Grey
shading indicates areas with insufficient model agreements on the
sign of change; stippling indicates areas with strong model agreement.
(Source: Figure SPM.5 in IPCC (2012) Special Report on Managing the
Risks of Extreme Events and Disasters to Advance Climate Change
Adaptation, http://ipcc-wg2.gov/SREX/.)
12
Sea Surface Temperatures (SSTs)
Observed Trends – Sea Surface Temperatures
FIGURE 13: Trends in annual SSTs (in degrees Celsius per
decade) over the period 1970 to 2011. (Source: Bureau of
Meteorology, http://www.bom.gov.au/climate/change/)
The trends in sea surface temperature (Figure 13) show a similar
pattern to that for other temperature parameters, that is, a
pronounced warming trend for the 1970–2011 period. Of
particular importance is that the warming trend adjacent to the
NSW south coast (0.20°C per decade) is higher than that for the
Gippsland coast, and indeed is the highest for any of Australia’s
coastal regions.
13
Future Trends – Sea Surface Temperatures
a) 2030
b) 2070
Increases from the 1990 baseline in SSTs of 0.3 to 2.0°C by
2030 are projected for the study areas (Figure 14a). These are
equivalent to a rate of 0.075 to 0.5°C per decade. As noted
previously, the observed rate of increase in SST adjacent to the
NSW South Coast was 0.2°C per decade for the past 40 years.
By 2070 (Figure 14b) the increase in SST is projected to range
from 0.3 to 4.0°C compared to a 1990 baseline.
FIGURE 14: Projected changes in SSTs in: (a) 2030 and (b) 2070
relative to the 1990 baseline. The 50th percentile (the mid-point of the
spread of model results) provides a best estimate result. The 10th and
90th percentiles (lowest 10% and highest 10% of the spread of model
results) provide a range of uncertainty. Emissions scenarios are from
the IPCC Special Report on Emission Scenarios: “Low emissions” –
B1 scenario; “medium emissions” – A1B scenario; and “high
emissions” – A1FI scenario. (Source: CSIRO & Bureau of Meteorology
(2007), Climate Change in Australia: http://www.climatechangeinaustralia.gov.au.)
14
Sea Level
Observed Trends – Sea Level
a) Global sea level change
a) Sea-level rise around Australia
The average global sea level (Figure 15a) has risen by about 210
mm (21 cm or 0.21 m) from 1880 to 2011, owing both to thermal
expansion from the warming of the ocean and the additional
water provided by melting glaciers and ice caps. The trend from
1993 to 2011 as measured by satellites (red line in the figure) is
about 3 mm per year, compared to the longer term average of
1.7 mm per year.
FIGURE 15: Observed global and regional sea-level rise: (a) Global
average sea-level measurements from tide gauges (blue) and satellites
(red). The blue shading indicates the accuracy of the tide-gauge
estimate. (b) The rate of sea-level rise around Australia as measured
by coastal tide gauges (circles) and satellite observations (contours)
from January 1993 to December 2011. (Source: CSIRO and BoM,
State of the Climate 2012, http://www.csiro.au/State-of-theClimate-2012.)
When compared to the global average rate of sea-level rise, there
is much variation around Australia’s coasts (Figure 15b), which is
crucial for understanding current and future risks associated with
rising sea level. For our study areas, the observed sea-level rise
from 1993 to 2011 is close to the global average of 3 mm year.
15
Future Trends – Sea Level
Projections for global average sea-level rise for 2100, compared
to the 1990 value, show a large range, from an additional 20 cm
to a maximum of 80 cm (Figure 16). Much of the uncertainty is
linked to the stability of the large polar ice sheets (Greenland and
Antarctica), where the dynamical processes by which they can
lose ice to the sea are not yet well understood. Thus, the IPCC
also notes that larger values (greater than 0.8 m) cannot be ruled
out. The observed sea-level rise (red line) is currently tracking
near the upper limit of the envelope of IPCC projections.
FIGURE 16: Global averaged projections of sea-level rise to 2100
relative to 1990 for several SRES scenarios. The continuous
coloured lines from 1990 to 2100 indicate the central value of the
projections, including the rapid ice contribution. The bars at right show
the range of projections for 2100 for the various SRES scenarios. The
horizontal lines/diamonds in the bars are the central values without
and with the rapid ice sheet contribution. The projections are based
on the IPCC Fourth Assessment Report. (Source: Church et al (2011):
http://www.cmar.csiro.au/sealevel.)
16
a) 2030
b) 2070
Figure 17 shows the difference from the projected global average
sea-level rise for areas around Australia. For our study areas, the
Australian regional projections show a further increase of 2.5–5.0
cm on top of the global average sea-level rise for 2030 (left panel)
and 5.0–7.5 cm for 2070 (right panel) for the southeast coasts.
This means that, for planning purposes, the maximum projected
sea-level rise for the study areas becomes about 20 cm in 2030
(compared to the 1990 baseline) and about 52 cm in 2070.
FIGURE 17: projected departures (in mm) from the: (a) 2030, and
(b) 2070, global-mean sea level from 17 SRES A1B simulations.
(Source: CSIRO and Antarctic Climate and Ecosystems (ACE) CRC
Sea-level rise website, http://www.cmar.csiro.au/sealevel/index.html)
However, because of the uncertainties in polar ice sheet
dynamics, higher values cannot be ruled out.
17
Coastal Inundation and Erosion
Inundation (flooding) of property and infrastructure (“high
sea-level events”) and coastal erosion are the most important
risks associated with a rising sea level.
1000
DARWIN
The flooding events are usually associated with high tides and
storm surges, with changes in sea level playing a role over longer
periods of time. Some estimates have been made of the
increased frequency of high sea-level events with realistic levels
of sea-level rise, that is, levels that are within the IPCC range of
projections for 2100 (Figure 18).
100
AUSTRALIA
A rise of 0.5 m (50 cm) in sea level can increase the frequency of
high sea-level events by a factor of 10 to 1000. These are
surprisingly high multiplication factors. A multiplying factor of 100
means that a flooding event that currently occurs once in every
hundred years would occur every year with a 0.5 m sea-level rise.
Although there are no estimates of these multiplication factors for
our study areas, the multiplication factors for Sydney and
Melbourne (from 100 to 1000) suggest the potential for a very
large increase in flooding events for the southeast Australian
coast towards the end of this century. Using a different approach,
the increase in the height of extreme storm tides (one-in-100-year
events) for the eastern Victorian coast has been projected for
2030 and 2070 (Table 1).
Many coastal flooding events are associated with simultaneous
high sea-level events and heavy rainfall events in the catchments
inland of the coastal settlements. Little research has yet been
done to connect these two phenomena and produce an overall
change in risk factor for these “double whammy” coastal flooding
events. For our study areas, and especially for the NSW south
coast, there is a strong correlation between storm surges and
heavy rainfall events as both are often caused by east coast low
pressure systems. Unfortunately, climate models cannot yet
simulate the behaviour of east coast lows so projections of
changes in their frequency or intensity cannot yet be made. Also,
no clear trends in changes in the nature of east coast lows are
evident from the observational record. Indirectly, the rises in sea
level over the 21st century, which are virtually certain, coupled
with the projections of a modest increase in the frequency of
heavy rainfall events for southern Australia (SREX) would suggest
that an increased risk of these “double whammy” flooding events
is more likely than not.
BUNDABERG
FREMANTLE
SYDNEY
ADELAIDE
MELBOURNE
TASMANIA
HOBART
FIGURE 18: Estimated multiplying factor for the increase in
frequency of occurrence of high sea-level events caused by a
sea-level rise of 50 cm (0.5 m). (Source: Dr John Hunter, ACE CRC,
http://www.acecrc.org.au/Research/Sea-Level%20Rise%20Impacts,
based on Hunter (2011).)
2030
2070
CURRENT
CLIMATE (m)
Low (m)
Med (m)
High (m)
Low (m)
Med (m)
High (m)
Port Welshpool
1.65
1.67
1.75
1.84
1.69
1.92
2.21
Port Franklin
1.87
1.88
1.98
2.07
1.90
2.15
2.48
Port Albert
1.75
1.77
1.87
1.96
1.79
2.04
2.36
Lakes Entrance
0.98
1.00
1.09
1.17
1.02
1.25
1.56
Metung
0.59
0.61
0.70
0.78
0.63
0.86
1.16
Paynesville
0.35
0.37
0.45
0.53
0.40
0.61
0.88
LOCATION
10
TOWNSVILLE
PORT HEDLAND
TABLE 1: Projected 100-year
return levels of storm tides for
selected locations along the
eastern Victorian coast under
current climate and 2030 and 2070
low, mid and high scenarios for
wind speed and sea-level rise (from
McInnes et al. 2005b). (Source:
CSIRO & Bureau of Meteorology,
Climate Change in Australia
website http://www.climatechangeinaustralia.gov.au.)
18
Bushfires
Although changes in the risk of bushfires can be expected as the climate warms,
observations of changed bushfire behaviour and projections of changes in the future have
large uncertainties.
The Black Saturday bushfires of 7 February 2009 in Victoria
illustrate the possible connections between climate change and
fire risk in areas very similar to the hinterlands of our study areas.
The four factors that form the MacArthur Forest Fire Danger
Index (FFDI) are directly related to climate, and three of them –
maximum temperature, relative humidity, and a drought factor –
all set record values on 7 February, values that are consistent
with the observed and projected trends in those variables due to
climate change (Karoly 2009). The FFDI itself set record levels,
ranging from 120 to 190 across sites in Victoria compared to a
value of 100, which was based on the FFDI for the Black Friday
fires of 1939.
The IPCC Fourth Assessment Report (IPCC 2007b) analysed the
climate-related factors that influence fire danger, and noted that
an increase in fire danger is likely to be associated with a reduced
interval between fires, increased fire intensity, faster fire spread
and a decrease in fire extinguishments. In our study areas, the
frequency of very high and extreme fire danger days is likely to
rise 4–25% by 2020 and 15–70% by 2050 (IPCC 2007b).
19
Other Climate-Related Risks
Confidence in projecting changes in the direction and magnitude of climate extremes
depends on many factors, including the type of extreme, the region and season, the amount
and quality of observational data, the level of understanding of the underlying processes,
and the reliability of their simulation in models.
Projected changes in climate extremes under different emissions
scenarios generally do not strongly diverge in the coming two to
three decades, but these signals are relatively small compared to
natural climate variability over this time frame. Even the sign of
projected changes in some climate extremes over this time frame
is uncertain. For projected changes by the end of the 21st
century, either model uncertainty or uncertainties associated with
emissions scenarios used becomes dominant, depending on the
extreme. Low-probability, high-impact changes associated with
the crossing of poorly understood climate thresholds cannot be
excluded, given the transient and complex nature of the climate
system. Assigning ‘low confidence’ for projections of a specific
extreme neither implies nor excludes the possibility of changes in
this extreme.
The IPCC Special Report on Emissions Scenarios (SREX)
provides estimates of global projected changes in other variables
not already covered earlier in this section and also indicates
where our current state of knowledge is insufficient to make
projections with any degree of confidence.
Examples, generally for the end of the 21st century and relative
to the climate at the end of the 20th century, include:
ff “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”
ff “There is low confidence in projections of small
spatial-scale phenomena such as tornadoes and hail…”
ff “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.”
ff “There is low confidence in projections of changes in
large-scale patterns of natural climate variability” [e.g., El
Niño]
Two of these are of particular relevance to the study regions.
Firstly, as much of the rainfall in the study regions, particularly in
the autumn-winter-spring, comes from frontal systems, any
southward shift in these storm tracks is likely to lead to further
reductions in rainfall. The southward shift in the sub-tropical ridge
and the resultant observed southward shift in storm tracks
appears to be one reason why the southeast Australian coast
has already observed rainfall declines.
Secondly, the low confidence in how the El Niño-Southern
Oscillation (ENSO) phenomenon will be affected by climate
change contributes to the uncertainty in future rainfall patterns in
the study regions. Although El Niño has more profound effects on
the weather of some other parts of Australia, it does also affect
the weather patterns experienced by the study regions. For
example, El Niño events are associated with moderate reductions
in winter and spring rainfall, whereas La Niña events, the
counter-parts of El Niño, are associated with moderate increases
in rainfall.
ff “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.” (Extra-tropical cyclones are intense
low-pressure systems that occur outside tropical areas,
such as over southern Australia.)
ff “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…”
20
Source Material and Background Reading
Church, J.A., J.M. Gregory, N.J. White, S.M. Platten and J.X. Mitrovica (2011), Understanding and Projecting Sea Level Change.
Oceanography (Journal of The Oceanography Society), 24(2), 130-143, doi:10.5670/oceanog.2011.33
CSIRO & Bureau of Meteorology (2007) Climate Change in Australia: http://climatechangeinaustralia.com.au/
CSIRO & Bureau of Meteorology (2012) State of the Climate 2012: http://www.csiro.au/Outcomes/Climate/Understanding/State-of-theClimate-2012.aspx
CSIRO & Antarctic Climate & Ecosystems (ACE) CRC, Sea-level rise website: http://www.cmar.csiro.au/sealevel/
Hunter J. (2011) A simple technique for estimating an allowance for uncertain sea-level rise. Climatic Change, DOI 10.1007/
s10584-011-0332-1.
IPCC (2000) Special report on emissions scenarios: A special report of Working Group III of the Intergovernmental Panel on Climate
Change. [Nakicenovic, N. and Swart, R. (eds.)]. Cambridge University Press: http://www.ipcc.ch/ipccreports/sres/emission/index.
php?idp=0
IPCC (2007a) Climate Change 2007: Synthesis Report. Contribution of Working Groups I, II and III to the Fourth Assessment Report of
the Intergovernmental Panel on Climate Change [Core Writing Team, Pachauri, R.K and Reisinger, A. (eds.)]. IPCC, Geneva,
Switzerland, 104 pp: http://www.ipcc.ch/publications_and_data/ar4/syr/en/contents.html
IPCC (2007b) Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of
the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and
H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 996 pp: http://www.ipcc.ch/
publications_and_data/ar4/wg1/en/contents.html
IPCC (2012) Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation. A Special Report of
Working Groups I and II of the Intergovernmental Panel on Climate Change [Field, C.B., V. Barros, T.F. Stocker, D. Qin, D.J. Dokken,
K.L. Ebi, M.D. Mastrandrea, K.J. Mach, G.-K. Plattner, S.K. Allen, M. Tignor, and P.M. Midgley (eds.)]. Cambridge University Press,
Cambridge, UK, and New York, NY, USA, 582 pp: http://ipcc-wg2.gov/SREX/
Karoly, D.J. (2009) The recent bushfires and extreme heat wave in southeast Australia. Bulletin of the Australian Meteorological and
Oceanographic Society, 22: 10–13: http://www.amos.org.au/documents/item/165
21