Climate Change in Australia

Changes to rainfall are possible but unclear. On annual and decadal basis, natural variability in the climate system can act to either mask or enhance any long-term human induced trend, particularly in the next 20 years.

Providing confident rainfall projections for Northern Australia is difficult because global climate models offer diverse results, and models have shortcomings in resolving some tropical processes. Natural climate variability is projected to remain the major driver of rainfall changes in the next few decades.

By late in the century, potential summer and autumn rainfall changes are approximately -20 to +10 per cent under an intermediate scenario (RCP4.5) and -30 to +25 per cent under a high emission scenario (RCP8.5). Impact assessment in this region should consider the risk of both a drier and wetter climate.

Average temperatures will continue to increase in all seasons (very high confidence).

There is very high confidence in continued substantial increases in projected mean, maximum and minimum temperatures in line with our understanding of the effect of further increases in greenhouse gas concentrations.

For the near future (2030), the annually averaged warming across all emission scenarios is projected to be around 0.5 to 1.3 °C above the climate of 1986 – 2005.

By late in the century (2090), for a high emission scenario (RCP8.5) the projected range of warming is 2.7 to 4.9 °C. Under an intermediate scenario (RCP4.5) the projected warming is 1.3 to 2.6 °C.

More hot days and warm spells are projected with very high confidence.

Extreme temperatures are projected to increase at a similar rate to mean temperature, with a substantial increase in the temperature reached on hot days, the frequency of hot days, and the duration of warm spells (very high confidence). For Darwin and Broome, for example, days with temperatures over 35 °C could be experienced for around a third of the year under an intermediate emission scenario (RCP4.5) by late in the century. For Cairns, days with temperatures over 35 °C could increase around 3-fold under intermediate emission scenario (RCP4.5) by late in the century.

Increased intensity of extreme rainfall events is projected, with high confidence.

Despite uncertainty in future projections of total rainfall for Northern Australia, an understanding of the physical processes that cause extreme rainfall, coupled with modelled projections, indicate with high confidence a future increase in the intensity of extreme rainfall events. However, the magnitude of the increases cannot be confidently projected. Drought will continue to be a feature of the regional climate variability, but projected changes are uncertain.

Mean sea level will continue to rise and height of extreme sea-level events will also increase (very high confidence).

For 1966 to 2009, the average rate of relative sea-level rise for Australia, from observations along the coast, was 1.4 mm/year. There is very high confidence in future sea-level rise. By 2030 the projected range of sea-level rise along the coasts of the Northern Australian coasts is 0.06 to 0.18 m above the 1986–2005 level, with only minor differences between emission scenarios. As the century progresses, projections are sensitive to concentration pathways. By 2090, the intermediate emissions case (RCP4.5) is associated with a rise of 0.27 to 0.65 m and the high case (RCP8.5) a rise of 0.38 to 0.87 m. Under certain circumstances, sea-level rises higher than these may occur.

Late in the century warming of the Northern Australian coastal waters poses a significant threat to the marine environment through biological changes in marine species, including local abundance, community structure, and enhanced coral bleaching risk. Sea surface temperature is projected to increase in the range of 2.2 to 4.1 °C by 2090 under a high scenario (RCP8.5). The sea will also become more acidic, with acidification proportional to emissions growth.

With medium confidence, fewer but more intense tropical cyclones are projected.

TROPICAL CYCLONES Tropical cyclones are projected to become less frequent, but the proportion of the most intense storms is projected to increase (medium confidence).

FIRE WEATHER See cluster level information for fire weather projections as the projections vary slightly in the two clusters.

HUMIDITY: There is little change projected in relative humidity until later in the century under a high emission scenario (RCP8.5), where a decrease in relative humidity is projected (medium confidence).

EVAPORATION: Potential evapotranspiration is projected to increase in all seasons as warming progresses (high confidence).

A continuation of the trend of decreasing winter rainfall is projected with high confidence. Spring rainfall decreases are also projected with high confidence. Changes to summer and autumn rainfall are possible but less clear. For the near future, natural variability is projected to dominate any projected changes.

In the near future (2030) natural variability is projected to predominate over trends due to greenhouse gas emissions. Understanding of physical rainfall processes (southward shift of winter storm systems), supported by climate model results, indicate rainfall decreases for winter and spring (high confidence), except for Tasmania in winter, where little change or increases are projected (medium confidence).

Early in the century (2030) and under all emission scenarios, winter and spring rainfall is projected to decrease by up to around 15 per cent. Late in the century, intermediate emissions (RCP4.5) are projected to lead to a projected decrease in winter rainfall of up to 20%, and under high emissions (RCP8.5) winter rainfall decline is projected to decrease by up to around 30%, with some important regional exceptions. Changes in autumn and summer are less clear, although statistical downscaling results suggest a continuation of the observed autumn declines.

Average temperatures will continue to increase in all seasons (very high confidence).

There is very high confidence in continued substantial increases in projected mean, maximum and minimum temperatures projected in line with our understanding of the effect of further increases in greenhouse gas concentrations.

For the near future (2030), the annually averaged warming across all emission scenarios is projected to be around 0.5 to 1.2 °C above the climate of 1986–2005.

By late in the century (2090), for a high emission scenario (RCP8.5) the projected range of warming is 2.7 to 4.2°C. Under an intermediate scenario (RCP4.5) the projected warming is 1.2 to 2.1 °C.

More hot days and warm spells are projected with very high confidence. Fewer frosts are projected with high confidence.

Extreme temperatures are projected to increase at a similar rate to mean temperature, with a substantial increase in the temperature reached on hot days, the frequency of hot days, and the duration of warm spells (very high confidence).

Frost risk days (minimum temperatures under 2 °C) are expected to decrease across the cluster (high confidence).

Increased intensity of extreme rainfall events is projected, with high confidence.

Even though annual mean rainfall is projected to decrease in the region, understanding of the physical processes that cause extreme rainfall, coupled with modelled projections indicate with high confidence a future increase in the intensity of extreme rainfall events. However, the magnitude of the increases cannot be confidently projected. Strongly decreasing mean rainfall in south west Western Australia gives us medium confidence in the projection of increased extreme rainfall for that region.

Time spent in drought is projected (with high confidence) to increase over the course of the century.

Mean sea level will continue to rise and the height of extreme sea-level events will also increase (very high confidence).

For 1966 to 2009, the average rate of relative sea-level rise for Australia, from observations along the coast, was 1.4 mm/year.

There is very high confidence in future sea-level rise. By 2030 the projected range of sea-level rise for the Southern Australian coastline is 0.07 to 0.19 m above the 1986–2005 level, with only minor differences between emission scenarios. As the century progresses, projections are sensitive to concentration pathways. By 2090, the intermediate emissions case (RCP4.5) is associated with a rise of 0.27 to 0.66 m and the high case (RCP8.5) a rise of 0.39 to 0.89 m. Under certain circumstances, sea-level rises higher than these may occur.

Late in the century warming of the Southern Australian coastal waters poses a significant threat to the marine environment through biological changes in marine species, including local abundance, community structure, and enhanced coral bleaching risk. Sea surface temperature is projected to increase in the range of 1.5 to 5.1 °C by 2090 under high emissions (RCP8.5). The sea will also become more acidic, with acidification proportional to emissions growth.

A harsher fire-weather climate in the future.

FIRE WEATHER: There is high confidence that climate change will result in a harsher fire-weather climate in the future. However, there is low confidence in the magnitude of the change to fire weather. This depends on the rainfall projection and its seasonal variation.

HUMIDITY AND SOLAR RADIATION: An increase in solar radiation and a decrease in relative humidity is projected in the cool season through the century (high confidence). This will be influenced by changes in rainfall (and associated changes to cloudiness) and temperature in the cluster. Changes in summer and autumn are less clear.

EVAPORATION: Potential evapotranspiration is projected to increase in all seasons as warming progresses (high confidence).

Changes to summer rainfall are possible but unclear. Winter rainfall is projected to decrease in the south with high confidence. For the near future, natural variability will dominate any projected changes.

In the near future (2030) natural variability is projected to predominate over trends due to greenhouse gas emissions. Winter rainfall in the south is projected to decline over the century under both intermediate (RCP4.5) and high (RCP8.5) emission scenarios (high confidence). There is a good understanding of the physical mechanisms driving this change (southward shift of winter storm systems together with rising mean pressure over the region).

Changes to annual and summer rainfall for late in the century are possible, but the direction of change cannot be confidently projected given the spread of model results. Impact assessment in this region should consider the risk of both a drier and wetter climate.

Average temperatures will continue to increase in all seasons (very high confidence).

There is very high confidence in continued substantial increases in projected mean, maximum and minimum temperatures in line with our understanding of the effect of further increases in greenhouse gas concentrations.

For the near future (2030), the annually averaged warming across all emission scenarios is projected to be around 0.6 to 1.4 °C above the climate of 1986–2005.

By late in the century (2090), for a high emission scenario (RCP8.5) the projected range of warming is 2.9 to 5.3 °C. Under an intermediate scenario (RCP4.5) the projected warming is 1.5 to 2.9 °C.

More hot days and warm spells are projected with very high confidence. Fewer frosts are projected with high confidence.

Extreme temperatures are projected to increase at a similar rate to mean temperature, with a substantial increase in the temperature reached on hot days, the frequency of hot days, and the duration of warm spells (very high confidence).

For Alice Springs, for example, days with temperatures over 35 °C could occur for more than a third of the year under an intermediate emission scenario (RCP4.5) by late in the century.

Where frosts (minimum temperatures under 2 °C) occur in the cluster, these are projected to decrease.

Increased intensity of extreme rainfall events is projected, with high confidence.

Understanding of the physical processes that cause extreme rainfall, coupled with modelled projections, indicate with high confidence a future increase in the intensity of extreme rainfall events, although the magnitude of the increases cannot be confidently projected.

Time spent in drought is projected, with medium confidence, to increase over the course of the century.

Mean sea levels will continue to rise and height of extreme sea-level events will also increase (very high confidence).

For 1966 to 2009, the average rate of relative sea-level rise for Australia, from observations along the coast, was 1.4 mm/year.

There is very high confidence in future sea-level rise. By 2030 the projected range of sea-level rise at Port Hedland is 0.07 to 0.17 m above the 1986–2005 level, with only minor differences between emission scenarios. As the century progresses projections are sensitive to concentration pathways. By 2090, the intermediate emissions case (RCP4.5) is associated with a rise of 0.28 to 0.65 m and the high case (RCP8.5) a rise of 0.40 to 0.85 m. Under certain circumstances, sea-level rises higher than these may occur.

Late in the century warming of the Rangelands coastal waters poses a significant threat to the marine environment through biological changes in marine species, including local abundance, community structure, and enhanced coral bleaching risk. Sea surface temperature is projected to increase in the range of 2.4 to 3.7 °C by 2090 under high emissions. The sea will also become more acidic, with acidification proportional to emissions growth.

FIRE WEATHER: Bushfire in the Rangelands depends highly on fuel availability, which mainly depends on rainfall. A tendency toward increased fire weather risk is expected in future, due to higher temperature and lower rainfall, but there is low confidence in the magnitude of fire weather projections.

HUMIDITY: Little change in relative humidity is projected for the near future (2030) while later in the century a decrease is projected in winter and spring (high confidence) and in summer and autumn (medium confidence).

SOLAR RADIATION: There is little change projected for solar radiation in the near future (2030), and for later in the century, increased radiation is projected in the south in winter (medium confidence).

EVAPORATION: Potential evapotranspiration is projected to increase in all seasons as warming progresses (high confidence).

Average winter and spring rainfall is projected to decrease with medium confidence. Changes in summer and autumn are possible but unclear. For the near future natural variability is projected to dominate any projected changes.

In the near future (2030) natural variability is projected to predominate over trends due to increasing greenhouse gas emissions. Late in the century, climate model results indicate decreasing winter rainfall, with high confidence in these projections in the more inland areas given the good understanding of the physical mechanisms driving this change (southward shift of winter storm systems together with rising mean pressure over the region). Only medium confidence in these projections is given for the more coastal regions taking into account uncertainty over driving processes and results from downscaling. Otherwise, there is low confidence in the direction of seasonal rainfall change due to strongly contrasting results from global climate models and downscaling approaches. The large uncertainty in this region is likely to be related to the range of rainfall drivers and competing influences on rainfall change as well as their relationship to topographical features such as the Great Dividing Range and Eastern Seaboard.

Impact assessment in this region should consider the risk of both a drier and wetter climate.

Average temperatures will continue to increase in all seasons (very high confidence).

There is very high confidence in continued substantial increases in projected mean, maximum and minimum temperatures in Eastern Australia, in line with our understanding of the effect of further increases in greenhouse gas concentrations.

For the near future (2030), the annually averaged warming across all emission scenarios is projected to be around 0.5 to 1.4 °C above the climate of 1986–2005.

By late in the century (2090), for a high emission scenario (RCP8.5) the projected range of warming is 2.8 to 5.0 °C. Under an intermediate scenario (RCP4.5) the projected warming is 1.3 to 2.6 °C.

More hot days and warm spells are projected with very high confidence. Fewer frosts are projected with high confidence.

Extreme temperatures are projected to increase at a similar rate to mean temperature, with a substantial increase in the temperature reached on hot days, the frequency of hot days, and the duration of warm spells (very high confidence).

Frost risk days (minimum temperatures under 2 °C) are expected to decrease (high confidence).

Some areas in the region could experience around two to three times the average number of days above 35 °C under intermediate emission scenarios by late in the century.

Increased intensity of extreme rainfall events is projected, with high confidence.

Understanding of the physical processes that cause extreme rainfall, coupled with modelled projections, indicate with high confidence a future increase in the intensity of extreme rainfall events, although the magnitude of the increases cannot be confidently projected.

Time spent in drought is projected, with medium confidence, to increase over the course of the century.

Mean sea level will continue to rise and height of extreme sea-level events will also increase (very high confidence).

For 1966 to 2009, the average rate of relative sea-level rise for Australia, from observations along the coast, was 1.4 mm/year. There is very high confidence in future sea-level rise. By 2030 the projected range of sea-level rise for the cluster coastline is 0.08 to 0.19 m above the 1986–2005 level, with only minor differences between emission scenarios.

As the century progresses, projections are sensitive to concentration pathways. By 2090, the intermediate emissions case (RCP4.5) is associated with a rise of 0.30 to 0.65 m and the high emissions case (RCP8.5) a rise of 0.44 to 0.88 m. Under certain circumstances, sea-level rises higher than these may occur.

Late in the century warming of the Eastern Australian coastal waters poses a significant threat to the marine environment through biological changes in marine species, including local abundance, community structure, and enhanced coral bleaching risk. Sea surface temperature is projected to increase in the range of 2.1 to 5.7 °C by 2090 under a high scenario (RCP8.5). The sea will also become more acidic, with acidification proportional to emissions growth.

A harsher fire-weather climate in the future.

FIRE WEATHER: There is high confidence that climate change will result in a harsher fire-weather climate in the future. However, there is low confidence in the magnitude of the change, as this is strongly dependent on the rainfall projection.

HUMIDITY: A decline in relative humidity is projected for winter and spring (high confidence) and summer and autumn (medium confidence), although changes in the near term are projected to be small.

EVAPORATION: Potential evapotranspiration is projected to increase in all seasons as warming progresses (high confidence).