Climate ScienceSummary of Latest Developments

A summary prepared by AGL – based upon IPCC and CSIRO research

For further information:

Tim NelsonHead of Economic Policy and Sustainabilitytanelson@agl.com.au

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The Greenhouse Effect – A Detailed Understanding

› Scientists are still perfecting their understanding of the world’s climate

› We know the two main influences of our planet’s temperature

» distance from sun

» composition of atmosphere

› ‘Radiative forcing’ is the change in the balance between solar radiation (heat and light) coming into the atmosphere and solar radiation going out

› The greenhouse effect refers to the ‘radiative forcing’ properties of the atmosphere

» greenhouse gases generally trap heat that is reflected off the Earth’s surface and trap it

» other gases (e.g. aerosols) and substances such as volcanic ash reflect heat before it enters the Earth’s atmosphere

› There is a clear relationship between the concentration of greenhouse gases in the atmosphere and the average global temperature

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Correlation between Carbon Dioxide and Temperature

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What are the Greenhouse Gases?

There are seven main greenhouse gases: water vapour, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons, perflurocarbons and sulphur hexafluoride (SF6).

Greenhouse Gas Global Warming Potential

(Radiative Forcing Potential)

Source of Greenhouse Gas

Carbon Dioxide 1 Carbon cycle, fossil fuels

Methane 23 Fossil fuels, waste

Nitrous Oxide 296 Fertiliser, industrial

Hydrofluorocarbons @ 100 to 12,000 Refrigeration, industrial

Perflurocarbons @ 5,000 to 12,000 Aluminium production

Sulphur hexafluoride 22,200 Dielectric fluid

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Increasing Concentrations of Greenhouse Gases

› Greenhouse effect is natural: it is what allows Earth to be habitable. It is the impact of humans on the greenhouse effect that is debated at present

› Global concentrations of greenhouse gases have increased markedly over the past century as a result of human activities. Concentrations now far exceed pre-industrial values

› The carbon dioxide concentration in 2009 of 386 parts per million (ppm) is much higher than the natural range of 170 to 300 ppm that has existed in the atmosphere for at least the past 800,000 years and possibly the past 20 million years

› CO2 emissions from the burning of fossil fuels increased by two per cent from 2007 to 2008, by 29 per cent between 2008 and 2000, and by 41 per cent between 2008 and 1990 - the reference year of the Kyoto Protocol

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Most Recent Observations

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Anthropogenic Changes to Radiative Forcing

The improved understanding of cooling and warming influences on climate has led scientists to conclude with very high confidence (9 out of 10 chance) that the global effect of human activities since 1750 has been one of warming, with a radiative forcing of + 1.6 W m-2.

Variable Current Radiative Forcing Other Information

Carbon dioxide, methane and nitrous oxide

+ 2.30 Wm-2 (+2.07 to +2.53) Rate of increase unprecedented in at least 10,000 years

Aerosols - 0.5 Wm-2 (-0.9 to –0.1) direct and –0.7 (-1.8 to –0.3) indirect

Aerosols also influence cloud lifetime and precipitation

Tropospheric ozone (i.e. nitrous oxide

etc)

+0.35 Wm-2 (+0.25 to +0.65)

Halocarbons +0.34 Wm-2 (+0.31 to +0.37)

Solar irradiance +0.12 Wm-2 (+0.06 to +0.30)

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Observed Climate Changes

› The scientific evidence points to positive radiative forcing as a result of human activities and natural phenomenon

› This positive radiative forcing is supported by emerging evidence of actual observed changes to the climate

› The linear trend increase in global average temperature is 0.740C (0.56 to 0.92)

› The linear warming trend for the last 50 years (0.130C per decade) is nearly twice that for the last 50 years

› Since 1960 the mean temperature in Australia has increased by about 0.7 °C .

› Average atmospheric water vapour content has increased, mountain glaciers and snow cover have declined in both hemispheres

› During 1993 to 2009 sea level rise has been 1.5 to 3mm per year in the south and east of Australia and 7 to 10mm per year in the north and west

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Observed Changes in Australia

Trend in mean temperature 1960-2009 (ºC/decade)Source: BOM-CSIRO

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Observed Changes in Australia

Trend in annual rainfall 1960-2009 (mm per decade) Source: BOM-CSIRO

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Link between Greenhouse Gases and Climate Change

› Most of the observed increase in globally averaged temperatures since the mid 20th century is “very likely” (greater than 9 in 10 chance) due to the observed increase in anthropogenic greenhouse gas concentrations

› Alternatively, it is extremely unlikely that global climate change of the past 50 years can be explained without external forcing

› Climate scientists believe that any increase in global temperature of 20C above pre-industrial levels is ‘dangerous’

» e.g. unstoppable loss of ice cover

› Based upon radiative forcing properties of greenhouse gases, a level of between 450 and 550 parts per million of carbon dioxide is necessary to prevent this ‘dangerous’ level being reached

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Forecast Temperature and Climate Changes

Even under the most optimistic scenarios, temperatures increase beyond 20C because the concentration of carbon dioxide increases above 550 parts per million.

Case Temperature Change (at 2090-2099 relative to 1980-1999)

Best Estimate Range

Constant Year 2000 Concentrations of GHG

0.6 0.3-0.9

Scenario 1 1.8 1.1-2.9

Scenario 2 2.4 1.4-3.8

Scenario 3 2.4 1.4-3.8

Scenario 4 2.8 1.7-4.4

Scenario 5 3.4 2.0-5.4

Scenario 6 4.0 2.4-6.4

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Impacts: Examples for Australia

› Australia will be hotter in coming decades

» Australian average temperatures are projected to rise by 0.6 to 1.5 ºC by 2030. If GHG emissions continue at current levels, warming is projected to be in the range of 2.2 to 5.0 ºC by 2070.

» Warming is projected to be lower near the coast and in Tasmania and higher in central and north-western Australia.

» These changes will be felt through an increase in the number of hot days.

› Much of Australia will be drier in coming decades

» In Australia compared to the period 1981-2000, decreases in rainfall are likely in the decades to come in southern areas of Australia during winter, in southern and eastern areas during spring, and in south-west Western Australia during autumn.

» An increase in the number of dry days is expected across the country, but it is likely that there will be an increase in intense rainfall events in many areas.

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Impacts: Examples for Australia

› River flow in the Murray-Darling Basin likely to decline 10-25% by 2050, with salinity change of -6 to +19%

› Inflows to Melbourne dams may drop 3-11% by 2020 and 7-35% by 2050

› More flash floods, erosion and landslides in some regions

› Coral reefs: bleaching an annual event by 2030-2050

› Alpine areas: 10-40% less snow-cover by 2020

› Rainforests: 50% reduction in habitat for endemic vertebrates for 1oC warming

› 15% drop in Australian pasture productivity and 12% drop in cattle weight for a 20% drop in rainfall

› Grain quality may decline due to reduced grain protein and more heat-shock proteins

› Significant drop in wheat yield likely in south-western Australia, while north-eastern areas are likely to have moderate increases in yield

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Conclusion

› It is very likely that human activities have caused most of the global warming observed since 1950

› There is greater than 90% certainty that increases in greenhouse gas emissions have caused most of the global warming since the mid-20th century.

› International research shows that it is extremely unlikely that the observed warming could be explained by natural causes alone.

› Evidence of human influence has been detected in ocean warming, sea-level rise, continental-average temperatures, temperature extremes and wind patterns.

› CSIRO research has shown that higher greenhouse gas levels are likely to have caused about half of the winter rainfall reduction in south-west Western Australia.

› AGL acknowledges the science of climate change – the AGL Greenhouse Gas Policy, August 2009.

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