2. Outline
• Evidence for climate change
Projections for the 21st century
•
• Potential impacts
• Conclusions
3. Outline
• Evidence for climate change
Projections for the 21st century
•
• Potential impacts
• Conclusions
4. Climate has always been variable. Ice ages occur every 100,000
years due to wobbles in the Earth’s orbit. Greenhouse gases and ice
sheets enhance the orbital effect on temperature by about 50%
Carbon dioxide and temperature
last 420, 000 years
350
20
temperature ( C)
300
o
CO2 (ppm)
? 250
10
200
0
150
-10 100
400,000 300,000 200,000 100,000 0
years before present
The present CO2 level of 380 ppm is unprecedented in at least the past
420,000 years and it is expected to rise to 550-950 ppm by the year 2100
Temperatures may rise by 1.4-5.8oC by 2100
5. In the past 200 years, concentrations of greenhouse
gases have continued to increase, and the Earth has
warmed. This is the enhanced greenhouse effect
The main greenhouse gases are water vapour, carbon dioxide, methane, nitrous oxide, ozone and CFCs
Carbon dioxide and temperature last 1000 years
Cape Grim and South Pole 350
temperature ( C)
Law Dome ice cores
1.0 temperature change
o
CO2 (ppm )
300
0.5
250
0.0
-0.5 200
1000 800 600 400 200 0
years before 2000 AD
Since 1750, carbon dioxide has risen 35%, methane 151%, nitrous oxide 17%, tropospheric ozone 36%
The temperature of the late 20th century is the highest in at least the past 1000 years
6. In the past 100 years, global average
surface temperatures have risen 0.7ºC
Difference from 1961-1990 average (oC)
1860 1880 1900 1920 1940 1960 1980 2000
The 12 warmest years on record have occurred since 1990 (WMO, 2005)
7. Over the past 50 years, global average sea-level
has risen 9 cm (1.85 mm/year)
Source: Church et al (2004)
8. Other evidence
• Warming of the upper 300 m of ocean
• Warming in the lowest 8 km of atmosphere
• Increase in extremely high temperatures, decrease in
extremely low temperatures
• More-intense rainfall and cyclones in many places
• Oceans are becoming more acidic due to higher CO2
• Snow cover and ice extent have decreased
• Shifts in plant and animal locations and behaviour
In Australia
• Warming of 0.9oC since 1910, mostly since 1950
• Min temps rising faster than max temps
• More heatwaves and fewer frosts
• More rain in the north-west, less in south and east since 1950
• Less extreme rainfall in the south and east since 1950
9. GHGs, aerosols,
Solar & volcanic ozone depletion
Most of the observed warming over the last 50 years is attributable to www.csiro.au
human activities that have increased greenhouse gas concentrations
10. Causes of Australian climate change
• Most of the warming is due to
human activities
• There is uncertainty about the
causes of Australian rainfall
trends
Increases in the northwest may
be due to natural variability and
a shift in weather patterns due
to increases in northern
hemisphere aerosols
Decreases in the south may be
due to natural variability,
increases in greenhouse gases
and ozone depletion
Decreases in the east are due
to an increase in El Niños
since 1975, the cause of which
is unknown
11. Outline
• Evidence for climate change
• Projections for the 21st century
• Potential impacts
• Conclusions
12. Climate change projections
• Rather than simply extrapolating observed trends, we use
computer models of the climate system driven by scenarios of
greenhouse gas and aerosol emissions, and ozone depletion
• Emission scenarios have various assumptions about
demographic, economic and technological change
13. Climate change projections
• Global warming of 0.5-1.2oC by 2030
and 1.2-3.8oC by 2070
• Sea level rise of 3-17 cm by 2030 and
7-50 cm by 2070
In Australia
• Warming of 0.5-2oC by 2030 and 1-6oC
by 2070
• Less frost and snow, more heatwaves
and fires
• Less annual total rainfall over
southern and eastern mainland
Australia, with increases over
Tasmania
• More frequent and intense droughts
• Increases in intensity of rain, floods,
tropical cyclones and storm surges
14. 2030 projections for Victoria
Feature Low Global Warming High Global Warming
Estimate of Uncertainty Estimate of Uncertainty
Change change
Annual average temperature +0.5 °C ±0.2°C +1.1°C ±0.4°C
Average sea level +3 cm +17 cm
Annual average rainfall -1.5% ±5% -3.5 % ±11%
Seasonal average rainfall Summer 0 ±6.5% - 0% ±15%
Autumn 1.5% ±5% -3.5% ±11%
Winter -1.5% ±5% -3.5% ±11%
Spring -5% ±5% -11% ±11%
Annual average potential evaporation +2.2% ±1.1% +5.0% ±2.5%
Annual average number of hot days +1 day +10 days (near coast)
(>35°C) + 20 days (inland)
Annual average number cold nights -1 day -10 days (inland)
(<0°C) - 20 days (highlands)
Annual average number of very high +1 day +11 days
b
& extreme forest fire danger days
Extreme daily rainfall intensity (1 in +5% +70%
c
20 year event)
Carbon dioxide concentration +73ppm +102ppm
b Results for 2020 C Results for 2050
For risk assessment, it is important to consider extreme scenarios, even though they
may have low probability (this is why we have insurance). Note the high global
warming including the uncertainty, e.g. annual average rainfall may decline by almost
15% and evaporation may rise by 7.5%
15. Outline
• Evidence for climate change
• Projections for the 21st century
• Potential impacts
• Conclusions
16. Potential impacts without adaptation
Key conclusions for Australia
• Most vulnerable ecosystems are wet tropics, Kakadu, alpine
areas, coral reefs, freshwater wetlands, and heathlands in
south-western Australia
• Generally less stream flow in southern and eastern Australia
• Crops may benefit from warmer conditions and higher CO2
but this may be offset by reduced rainfall
• Greater exposure of infrastructure to extreme weather events
and sea-level rise
• Greater exposure to heat-related deaths and dengue fever
A few examples follow for Victoria
17. Water
Water resources are likely to be further
stressed due to projected growth in
demand and climate-driven changes in
supply for irrigation, cities, industry and
environmental flows
A decrease in annual rainfall with higher
evaporative demand leads to a decrease in
run-off into rivers, i.e. a decline of 0-45% by
2030 in 29 Victorian catchments. For
Melbourne, average stream-flow is likely to
drop 3-11% by 2020 and 7-35% by 2050
Droughts are likely to become more
frequent and more severe, with increased
fire risk affecting water yield and quality in
fire-affected catchments
A 10-40% reduction in snow cover is likely
by 2020
18. Heat
Victoria is likely to become warmer, with more hot days and fewer
cold nights
For example, the number of days above 35ºC could average 10-16
in Melbourne (now 9) and 36-50 in Mildura (now 33), while the
number of days below 0ºC in Mildura could average 1-4 (now 6)
Increased peak summer energy demand for cooling is likely, with
reduced energy demand in winter for heating
Warming and population growth may increase annual heat-
related deaths in those aged over 65, e.g. from 289 deaths at
present in Melbourne to 582-604 by 2020 and 980-1318 by 2050
Higher temperatures may also contribute to the spread of vector-
borne, water-borne and food-borne diseases
19. Agriculture
Controlled experiments have shown grain yield
increases under elevated atmospheric carbon dioxide
concentrations. However, it is not known whether this
will translate to field conditions in Australia due to
nutrient limitations and elevated temperatures.
Low to moderate warming may also help plant growth
especially frost sensitive crops such as wheat, but more
hot days and a decline in rainfall or irrigation could
reduce yields. Warmer winters can reduce the yield of
stone fruits and apples that require winter chilling.
Grape quality is likely to decline.
Livestock would be adversely affected by greater heat
stress.
In forestry, the CO2 benefits may be offset by increased
bushfires and changes in pests.
20. Cities
Changes in average climate
and sea-level will affect
building design, standards
and performance, energy and
water demand, and coastal
planning
Increases in extreme weather
events are likely to lead to
increased flash flooding,
strains on sewerage and
drainage systems, greater
insurance losses, possible
black-outs, more fires and
challenges for emergency
services.
21. Conclusions
Climate change is real and underway
Most of the warming of the past 50 years is due to
human activities
Climate change will continue in the 21st century
Warmer and drier conditions are expected, with more
extreme events
Significant impacts are likely
Risk management requires consideration of low
probability, high impact scenarios
