www.csiro.au

Climate science overview

Kevin Hennessy

Melbourne, 5 June 2006

Outline• Evidence for climate change

• Projections for the 21st century

• Potential impacts

• Conclusions

Outline• Evidence for climate change

• Projections for the 21st century

• Potential impacts

• Conclusions

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

100

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0100,000200,000300,000400,000years before present

CO

2 (pp

m)

-10

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20

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pera

ture

(o C)

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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

In the past 200 years, concentrations of greenhouse gases have continued to increase, and the Earth has warmed. This is the enhanced greenhouse effect

Carbon dioxide and temperature last 1000 years

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02004006008001000years before 2000 AD

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m)

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(o C)

Cape Grim and South PoleLaw Dome ice corestemperature change

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

The main greenhouse gases are water vapour, carbon dioxide, methane, nitrous oxide, ozone and CFCs

In the past 100 years, global average surface temperatures have risen 0.7ºC

The 12 warmest years on record have occurred since 1990 (WMO, 2005)

1860 1880 1900 1920 1940 1960 1980 2000

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om 1

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1990

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(oC

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Over the past 50 years, global average sea-level has risen 9 cm (1.85 mm/year)

Source: Church et al (2004)

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

www.csiro.auMost of the observed warming over the last 50 years is attributable to human activities that have increased greenhouse gas concentrations

Solar & volcanicGHGs, aerosols, ozone depletion

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 Niñossince 1975, the cause of which is unknown

Outline• Evidence for climate change

• Projections for the 21st century

• Potential impacts

• Conclusions

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

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 2070In 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

2030 projections for Victoria

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%

b Results for 2020 C Results for 2050

Feature Low Global Warming

Estimate of Uncertainty Change

High Global Warming

Estimate of Uncertainty 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 Autumn Winter Spring

0 ±6.5% -1.5% ±5% -1.5% ±5% -5% ±5%

0% ±15% -3.5% ±11% -3.5% ±11% -11% ±11%

Annual average potential evaporation +2.2% ±1.1% +5.0% ±2.5% Annual average number of hot days (>35°C)

+1 day +10 days (near coast) + 20 days (inland)

Annual average number cold nights (<0°C)

-1 day -10 days (inland) - 20 days (highlands)

Annual average number of very high & extreme forest fire danger daysb

+1 day +11 days

Extreme daily rainfall intensity (1 in 20 year event)c

+5% +70%

Carbon dioxide concentration +73ppm +102ppm

Outline• Evidence for climate change

• Projections for the 21st century

• Potential impacts

• Conclusions

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

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 likelyby 2020

HeatVictoria 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

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.

CitiesChanges 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.

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

Thank you