2 What do we know about it?

Strong and clear evidence supporting climate change science has been derived from a range of sources, including our historic climate record (palaeoclimatic evidence from tree rings and lake sediments, etc.), climate measurements from the recent past and sophisticated climate models. A number of scientific disciplines contribute to our understanding of climate change, including atmospheric physics, chemistry, biology, oceanography, hydrology and geology.

2.1 Past climate change

Climate change refers to long-term change in the average pattern of weather over decades or longer. Earth’s climate has varied enormously many times since Earth formed 4.5 billion years ago; it has been both warmer and cooler than today, driven by changes in the sun’s intensity, Earth’s orbit around the sun, the changing configuration of continents and oceans, and natural variations in the level of greenhouse gases in the atmosphere (Australian Academy of Science 2010, CSIRO 2011).

The geological records show us that past temperature changes have affected the world dramatically, altering atmospheric and oceanic circulation, rainfall patterns and water availability, ice cover, vegetation, ocean acidity and sea level. Past climate change also shows us that global climate is sensitive to small influences (Australian Academy of Science 2010). Processes similar to past climate change can act to amplify current human influences.

Our evolutionary history can be, at least in part, linked to past climate change, with a growing body of work in palaeoanthropology showing a correlation between evolutionary events and times of natural climatic variability. Modern human civilisation has evolved and developed during a relatively stable period of climate following the last glacial period, known as the Holocene. Humanity has dealt with small variations in climate in the past. However, recent human-induced climate change presents a challenge for today’s much larger and more urbanised population, which depends on complex infrastructure and globally interdependent agricultural systems (CSIRO 2011).

2.2 Current climate change

Our current climate is changing far more rapidly than in the geological past. Global average temperatures both on land and over the ocean rose by just over 0.7 °C in the 100 years from 1910 to 2009 (Figure 1). Average surface air temperature has increased by nearly 1 °C in Australia and South Australia, higher than the global average, and will continue to rise (Climate Commission 2011a, CSIRO 2011). The rate of global warming is increasing, with the past 50 years warming at nearly twice the rate as over the past 100 years (CSIRO 2011). South Australian average temperatures have been rising steadily since the 1970s, and temperatures for the past decade (2001 to 2010) were the warmest since records began in 1900 (BoM 2011). There has been a clear decline in average rainfall in southern Australia since 1970, which has been linked to rising temperatures, and this drying trend is likely to persist.

Around the world, many changes have been observed that are consistent with the increase in global average temperature: warming oceans, widespread retreat of mountain glaciers and ice caps, ice loss from the Greenland and Antarctic ice sheets, sea level rise, continued decreases in the extent and volume of arctic sea ice, increasing water vapour in the atmosphere, decreasing ocean alkalinity, shifting weather systems, and changes to animal and plant behaviour (Australian Academy of Science 2010).

Graph of global annual, and five-year running, mean surface air temperature change from 1880s to the present, showing an increasing trend.

Note: The blue bars show uncertainty estimates.

Source: NASA and GISS (2012)

Figure 1 Global annual mean surface air temperature change, 1880s to the present

2.2.1 Causes of climate change

Greenhouse gases are those gases in Earth’s atmosphere that selectively absorb radiation. They are transparent to incoming short-wave solar radiation but absorb the longer wavelength radiation emitted by Earth. This means that atmospheric greenhouse gases have little effect on incoming solar radiation but absorb outgoing radiation, thereby warming the lower atmosphere and surface of the planet. The basic physical principle—that greenhouse gases such as carbon dioxide trap energy emitted by Earth and keep the planet warmer than it otherwise would be—was established more than a century ago.

There is compelling evidence that the recent global warming is being caused largely by human emissions of greenhouse gases, emitted since the start of the agricultural and industrial revolutions (Australian Academy of Science 2010). Scientific understanding of anthropogenic climate change has been built over a long period and continues to advance strongly.

Given the complexity of the climate system, some uncertainties remain in the science of climate change, but these relate more to precise timescales or magnitudes of expected future impacts and do not affect the major conclusions (Australian Academy of Science 2010, Climate Commission 2011b).

2.2.2 The future of climate change

Projections of future climate are dependent on the level of future human greenhouse gas emissions and how the climate system responds to these emissions. It should be noted that there is generally a significant period of time before changes to the inputs of the climate system result in changes to the system. As a result of these long system lags, existing greenhouse gas concentrations in the atmosphere will commit Earth to a further warming of 0.5 °C, irrespective of future levels of emissions (CSIRO 2011).

A number of future greenhouse gas emission scenarios have been published by the Intergovernmental Panel on Climate Change (IPCC) (Box 2). Climate models have enabled projected warming to be estimated for these different emissions scenarios. While it is considered too early to reliably assess which emissions scenarios are the more likely, the lack of global effort to reduce emissions has focused recent attention on the high-end scenarios for mapping our future (Betts et al. 2011). Since the emissions pathways were produced in 2000, there have been unprecedented increases in global emissions of greenhouse gases, reflecting ongoing high emissions levels in developed nations, coupled with the very rapid industrialisation of many developing nations, particularly China and India (Anderson and Bows 2011). Not only are global emissions increasing, but the rate at which they are increasing is growing. Between 2003 and 2007, actual emissions rose at a rate faster than the highest emissions scenario (A1FI) and, despite a temporary slowdown due to the global recession, emissions growth reached a record high in 2009 and 2010 (IEA 2011, Peters et al 2012).

In the late 1990s, a globally averaged warming of 2 °C above pre-industrial levels was proposed as the guardrail beyond which the effects of climate change start to have dangerous risks and impacts on water supplies, ecosystems, food production, coasts and human health (Council of the European Union 2004, CSIRO 2011). The characterisation of 2 °C as the threshold between acceptable and ‘dangerous’ climate change is premised on an early assessment of the scope and scale of the accompanying impacts. More recent research, however, has revised the impacts associated with 2 °C sufficiently upwards that ‘2 °C can now be regarded as extremely dangerous’ (Anderson and Bows 2011). A 2 °C warming may not sound significant—we are used to greater temperature fluctuations on a day-to-day basis—but normal weather variability should not be confused with a sustained increase in average global temperature. The difference in average global temperature between an ice age and an interglacial period is only 5 °C.

Because future temperature increases correlate closely with the cumulative emissions of the main greenhouse gas—carbon dioxide—the dramatic emissions growth in developing nations highlights the urgent mitigation task before us. Reducing the emissions of carbon dioxide will only slow the rate of increase of atmospheric concentrations, rather than stabilise them. Stabilising atmospheric concentrations requires emissions to be reduced to very near zero and even, depending on timescales and pathways to stabilisation, for some existing greenhouse gases to be removed from the atmosphere. The latest scientific assessments emphasise that long-term gradual reductions in global greenhouse gas emissions are insufficient—rapid, deep and ongoing reductions are required (Climate Commission 2011b, CSIRO 2011, Garnaut 2011, New et al. 2011). A number of recent analyses suggest that, without immediate, concerted mitigative action at a global scale, there is now little to no chance of maintaining the global mean surface temperature increase at or below 2 °C, and temperature rises of 3 °C or 4 °C (relative to the pre-industrial period) by as early as 2060–70 are much more likely (Anderson and Bows 2011, Betts et al. 2011, Climate Commission 2011b, CSIRO 2011, New et al. 2011).

Given the difficulty of achieving rapid and large reductions in global emissions, we need to increase our understanding of the impacts of high-end climate change and the implications these have for adaptation planning.

2.3 Concentrations of greenhouse gases

Earth’s atmosphere consists mainly (about 99%) of nitrogen and oxygen—non-greenhouse gases that exert almost no warming effect. The natural greenhouse effect is caused by several different gases that exist in very small concentrations but act to maintain a warmer, life-supporting temperature on Earth. Atmospheric concentrations of greenhouse gases are the net result of emissions of gases (sources) and the removal of gases from the atmosphere (sinks). Human activities have increased the concentration of greenhouse gases by increasing sources of greenhouse gases, such as the burning of fossil fuels and industrial processes (e.g. cement production), and reducing sinks through changed agricultural practices and deforestation.

Atmospheric concentrations of greenhouse gases are known from recent measurements taken at a number of monitoring stations around the world (including Cape Grim in Tasmania) and, for past eras, from the analysis of air trapped in ice cores (Figure 2). These observations reveal that atmospheric concentrations of greenhouse gases have been rising over the past 250 years, but particularly in the past few decades, after being relatively stable since the end of the last ice age.

Water vapour, which exists naturally in the lower atmosphere as part of the water cycle, is the most abundant greenhouse gas and accounts for about half of the present-day greenhouse effect (Australian Academy of Science 2010). It is an important greenhouse gas because, although it is not directly influenced by humans, its atmospheric concentration increases as the atmosphere warms, providing an amplifying effect.

The second most prevalent greenhouse gas in the atmosphere is carbon dioxide (CO2), which contributes about 64% of radiative forcing—the influence of greenhouse gases on Earth’s temperature (WMO 2011). CO2 is also an important gas because a significant fraction remains in the climate system for hundreds to thousands of years (Australian Academy of Science 2010). The influence of CO2 on the radiation balance of Earth is the largest single contributor to human-induced climate change (CSIRO 2011).

CO2 is constantly transferred between the atmosphere, oceans and land vegetation as part of the natural carbon cycle. Before human influences, these natural exchanges were largely in balance. Since industrialisation, CO2 concentrations have increased by about 40%, from 278 parts per million (ppm) in the mid-18th century to 389.6 ppm in June 2012 (CSIRO 2012a). CO2 levels are rising mainly as a result of the burning of fossil fuels (increasing sources of greenhouse gases) and deforestation (reducing sinks). The Northern Hemisphere’s CO2 concentration, as measured at Mauna Loa Observatory in Hawaii, peaked at 400 ppm on 4 May 2013, 25% higher than in 1960, and increasing at a faster rate than previously. (Continuous monitoring at the observatory started in 1956.) The concentration of CO2 falls during the Northern Hemisphere’s summer when plant growth absorbs the gas, and then goes up again during the colder seasons.

Just over half of the emissions of CO2 have been absorbed by natural ocean and land sinks, with the remaining 45% remaining in the air and causing atmospheric concentrations to rise (Australian Academy of Science 2010). There has been a recent acceleration of CO2 emissions since 2000, coinciding with a period of rapid economic growth in China, India and developing economies (CSIRO 2011).

Methane (CH4) is the next most important greenhouse gas in terms of its impact on the radiative imbalance, contributing about 18% (WMO 2011). Although at a lower concentration in the atmosphere, CH4 has a much higher warming effect than CO2 for a given mass. Wetland emissions are the dominant natural source, but, in recent decades, emissions from human activities exceeded those from natural sources by two-fold or more (CSIRO 2011). Atmospheric concentrations of CH4 have increased by more than 150% since industrialisation to 1763.7 parts per billion (ppb) in June 2012. Human-induced CH4 emissions arise from ruminant livestock production; rice cultivation; landfill waste; losses from coal, oil and gas extraction; and biomass burning. CH4 is removed from the atmosphere through chemical degradation.

Box 2 Intergovernmental Panel on Climate Change emissions scenarios

A number of future greenhouse gas emissions scenarios were published by the Intergovernmental Panel on Climate Change (IPCC) (IPCC 2000). The IPCC was jointly established by the World Meteorological Organization and the United Nations Environment Programme to assess the scientific, technical and socio-economic information relevant for understanding the risk of human-induced climate change (IPCC 2000). The IPCC emissions scenarios are based on observed emissions until 2000 and then reflect different assumptions about future global population, economic growth and technological development (Betts et al. 2011).

The projected emissions from the IPCC special report are shown in Figure A. Since 2005, global GHG emissions have continued to track above the middle of the IPCC’s scenario range—between A1B and A1FI.

The A1FI emissions scenario is the highest emissions category, characterised by an integrated world with rapid economic growth, an emphasis on fossil fuels and a global population that reaches 9 billion in mid-century. The A1FI scenario is considered by the IPCC to be one of a number of plausible future greenhouse gas projections if our global society does not take mitigative action.

Graph of the global industrial carbon dioxide emissions for 1990–2008 and 2009 for different emissions scenarios, showing an increasing trend for all scenarios

Source: Manning et al. (2010)

Note: Black circles represent the years 1990–2008, and the open circle represents 2009. Emissions fall within the range of all 40 emission scenarios (grey shaded area) and six illustrative marker scenarios (coloured lines) of the IPCC special report. The inset in the upper left corner shows these scenarios to the year 2000.

Figure A Annual industrial carbon dioxide (CO2) emissions for 1990–2008 and 2009

The best IPCC estimate of future warming for A1FI is a 4.5 °C global average surface temperature increase above pre-industrial levels (or 4 °C above 1980–99 levels; Figure A), with a likely range of 2.9–6.9 °C above pre-industrial levels by 2100 (IPCC 2000, 2007). Since the release of the fourth IPCC assessment report, produced in 2007, evidence available from the more recent climate models supports a best estimate of around 5 °C rise relative to pre-industrial temperatures by the 2090s, with a temperature rise of 4 °C by the 2070s. If carbon cycle feedbacks are strong, the 4 °C could be reached in the 2060s (Betts et al. 2011). The other scenarios describe a world with lower emissions and corresponding temperature rises, reflecting differing rates of change in economic structures and different adoption of clean and efficient technologies.

Recently, the IPCC has established a new set of emissions pathways, known as the Representative Concentration Pathways, as the basis for the next stage of scenario modelling and impact assessment (Moss et al. 2010). These differ from the earlier emissions pathways in that they are based on different levels of planned mitigation and consider a wider range of greenhouse gas concentrations.

The long-term upward trend in CH4 atmospheric levels slowed between 1999 and 2006 but has been increasing again since 2007. Scientists are currently investigating the possible role of the thawing of the CH4-rich northern permafrost in this recent increase.

Human-made synthetic greenhouse gases—chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs)—which are used in refrigeration and air-conditioning systems, contribute about 12% to radiative imbalance. Although CFC concentrations are decreasing in the atmosphere as a result of international action to protect the ozone layer, concentrations of HCFCs and HFCs, which are less damaging to the ozone layer and so are being used to replace CFCs, are rapidly increasing. These are potent greenhouse gases with much longer atmospheric lifetimes than CO2.

Nitrous oxide (N2O) has contributed about 6% of the overall global increase in radiative imbalance, and concentrations have increased by 20% since industrialisation, to 324.1 ppb. Agriculture is the main anthropogenic source of N2O emissions, including soil cultivation, fertiliser use and livestock manure management. Fossil fuel burning also produces N2O (WMO 2011).

	Graph of carbon dioxide concentrations, methane concentrations and nitrous oxide measured at Cape Grim since 1976, with earlier measurements from samples taken at Law Dome (Antarctica) showing a steep increase since the 1800s.

Note: Cape Grim measurements are from 1976; older measurements are based on air extracted from ice samples collected from Antarctica (Law Dome).

Sources: Bureau of Meteorology, CSIRO (2012a)

Figure 2 Atmospheric concentrations of carbon dioxide, methane and nitrous oxide

2.4 Observed and projected changes in climate

Global climate change will affect South Australian temperature and rainfall.

2.4.1 Temperature

The average South Australian surface air temperature has risen by just under 1 °C over the past 100 years (Climate Commission 2011a), a greater increase than the global average value of about 0.7 °C. Most of this increase has occurred in the second half of the 20th century, and this trend is continuing. The past decade (2000–09) has been the warmest since records began in 1900 (CSIRO 2011). From around 1950, there has been a steady temperature rise—approximately 1 °C—in South Australia (Figure 3).

Minimum (overnight) temperatures increased more rapidly than maximum (daytime) temperatures over most of the 20th century. There has also been an overall increase in the frequency of heatwaves, while the frequency of extremely cold weather has decreased (CSIRO 2011).

The rate of warming of the atmosphere has been moderated by the vast amounts of heat that the oceans have absorbed in recent decades. The upper layer of the ocean has warmed significantly, and recent observations indicate that warming of the deeper waters of both the Southern and Atlantic oceans is also occurring (Climate Commission 2011b).

Global sea surface temperatures also show a warming trend, rising on average by 0.7 °C, while the temperatures of the surface waters surrounding Australia have increased by about 0.9 °C since 1900 (CSIRO 2011).

The latest best estimates for projected additional average temperature increases for South Australia from 1990 to 2030 range from 0.8 °C to 1.5 °C, depending on region and emissions scenario (Table 1). By 2070, additional warming is expected to be between 1.2 °C and 3.5 °C, compared with 1990. These regional temperature projections have been produced by the South Australian Research and Development Institute (SARDI) from a synthesis of the projections contained in the 2006 CSIRO report Climate change under enhanced greenhouse conditions in South Australia (Suppiah et al. 2006), and the 2007 CSIRO and Bureau of Meteorology Climate change in Australia: technical report. These reports are based on global climatic models prepared for the IPCC (SARDI 2010).

Map of trend in mean surface air temperature for South Australia over past 40 years showing a warming trend.

Source: Climate Commission (2013)

Figure 3 Long-term trend in South Australia’s average temperature, measured as the difference from the 1961–90 average

Table 1 Best estimate of the range of annual average additional temperature increase in South Australia (relative to 1990) for low–high emissions scenario

South Australian NRM region



Note: The temperature ranges are best estimates based on the 50th percentile and range from a low emissions to a high emissions scenario. See the source document for a description of the methods and a full range of results. Note also that the 2030 estimates are largely insensitive to future emissions because of the lag times of the climate system, and therefore show little or no difference under the low and high emissions scenarios. There is some uncertainty in the regional projections as they are based on low-resolution global model results that may not accurately represent regional outcomes.

Source: SARDI (2010)

Adelaide and Mount Lofty Ranges



Alinytjara Wilurara



Eyre Peninsula



Kangaroo Island



Northern and Yorke



SA Arid Lands



SA Murray–Darling Basin



South East



2.4.2 Rainfall

Australia’s rainfall has changed over recent decades, with a general trend towards decreasing late autumn and winter rainfall over the south, east and western fringes, but increasing spring and summer rainfall in many parts of the north and west (Figure 4). There has been a clear decline in South Australian rainfall since 1970, which has been linked, at least in part, to changes in large-scale atmospheric circulation associated with global warming (CSIRO 2010).

Year-to-year and decadal rainfall in Australia is influenced by several modes of natural variability caused by changes in relative sea surface temperatures and atmospheric circulation patterns; this results in Australia’s rainfall being naturally highly variable over time and from region to region. The modes of variability with the most important impact on Australian rainfall are the El Niño–Southern Oscillation, relating to the tropical Pacific Ocean; the Indian Ocean Dipole; and the Southern Annular Mode, which operates in the higher latitudes (Climate Commission 2011b).


Annual Rainfall - Total for Australia from 1970


Annual Rainfall - Total for South Australia from 1970

Source: BoM (2012a)

Figure 4 Trends in (a) Australian and (b) South Australian total annual rainfall (millimetres per 10 years), 1970–2011

Although it has been difficult to distinguish human influences on rainfall from natural variations (this is an area of active research), a number of recent studies have detected likely signals of climate change. In particular, a pronounced drying trend that is large compared with historical natural variations has emerged over the past 15–30 years in south-eastern Australia and the south-west of Western Australia (CSIRO 2011).

Higher temperatures and warming oceans affect atmospheric circulation and may be altering the behaviour of these natural modes (IPCC 2010). The Southern Annular Mode (also known as the Antarctic Oscillation) reflects the north–south movement of strong westerly winds in the mid to high latitudes of the Southern Hemisphere that bring storm systems, cold fronts and rainfall to southern Australia. Over the past several decades, there has been an increasing tendency for this mode to remain in a ‘positive’ phase, with the westerly winds remaining contracted towards the Antarctic, leading to reduced winter rainfall over southern Australia (BoM 2012b).

The Indian Ocean Dipole is a measure of differences in the temperatures of the western and eastern equatorial Indian Ocean. A ‘positive’ event is caused by warmer than usual waters in the tropical west, and cooler than normal waters (due to altered ocean circulation) in the tropical east. This is associated with a reduction in late winter and spring rainfall over southern Australia. The number of positive events has been increasing since 1950 (reaching a record high frequency over the past decade), while the number of negative events (bringing increased rainfall) has been decreasing (Abram et al. 2008, Cai et al. 2008, Ihara et al. 2008, BoM 2012c).

There is some evidence to suggest that global warming is increasing the likelihood of dry states associated with the El Niño–Southern Oscillation (CSIRO 2010), by causing a weakening of the Walker Circulation in the Pacific and leading to conditions similar to the El Niño phase of the Southern Oscillation. El Niño events are linked to lower spring and summer rainfall in Australia. Climate model forecasts support this weakening over coming decades, but the research in this area is ongoing and is still not settled (Darren Ray, Senior Meteorologist/Climatologist, South Australian Regional Climate Services Centre, Bureau of Meteorology, pers. comm., 24 April 2010).

Recent research has also shown that much of the observed rainfall decline since 1970 in southern South Australia and Victoria is linked to changes in atmospheric circulation via an expansion of the tropics (CSIRO 2010, 2012b). The Hadley Circulation is a fundamental part of the global climate system. It is the atmospheric circulation that transports warm, dry air poleward from the equator. As this cools and sinks, it creates an east–west band of high atmospheric pressure known as the subtropical ridge over the mid-latitudes of both hemispheres (including southern Australia) and is responsible for the relative aridity at these latitudes.

During the warmer half of the year (November to April), the subtropical ridge sits south of the Australian continent and acts to block southern rain-bearing fronts. It then moves north during the cooler months, thereby allowing autumn and winter rains to reach southern Australia. The intensity of the subtropical ridge has been expanding and increasing in strength since 1970, and this correlates well with rising global temperatures over this time. The 13-year period from 1997 to 2009, known as the millennium drought, was the driest in the last 110 years of rainfall records. The millennium drought was unprecedented in that it was largely constrained to southern Australia; there was an absence of wet months and wet years; and the seasonal pattern of rainfall decline differed from previous droughts, with reductions occurring mainly in autumn. The change in seasonality of rainfall contributed to a disproportionately high drop in stream flow: soils were drier at the start of the run-off season because more winter rain was taken up by vegetation and dry soils (CSIRO 2011, 2012b).

Adelaide skyline

Barbara Hardy Institute

One of the implications of these findings for water planning and management is that the traditional filling season of water supply systems across most of south-eastern Australia may not be as reliable in the future. It is also uncertain to what extent the reduced cool-season rainfall will be offset by higher warm-season falls. The expansion of tropical influences on climate will be important in influencing stream flow. Record rainfalls in 2010–11 were brought about by a strong La Niña event (the wet phase of the El Niño–Southern Oscillation), and wet phases of the Indian Ocean Dipole and the Southern Annular Mode, coupled with the warmest sea surface temperatures on record to the north of Australia. Abundant rainfall can still be expected even if, overall, the climate becomes drier. In 2011, late autumn and winter rainfalls continued to be below average, consistent with the expansion of the Hadley Circulation (CSIRO 2012b).

Rainfall predictions do not have as high a degree of confidence as temperature predictions; however, all global climate models generally agree that there will be decreased rainfall in the mid-latitudes, where southern Australia sits (CSIRO 2011). Consequently, South Australia’s drying trend is likely to continue, and this, together with higher temperatures, poses significant risks to agriculture and urban water supplies (Climate Commission 2011a).

Estimates for reductions in rainfall for South Australia vary by region, but show the possibility of decreases in annual rainfall across all regions of South Australia, particularly in autumn and winter. Since rainfall is much harder to predict than temperature, the range of possibilities is relatively large compared with temperature projections. The estimates in Table 2 have been produced by the South Australian Research and Development Institute. Since they are based on low-resolution global model results, caution should be exercised, as they may not accurately represent regional outcomes.

Table 2 Best estimate of the range of additional rainfall reductions (relative to 1990) for a low–high emissions scenario

South Australian natural resource management region



Note: These rainfall reduction ranges are a best estimate based on the 50th percentile and range from a low emissions to a high emissions scenario. See the source document for the full range of results. Note also that the 2030 estimates are largely insensitive to future emissions and therefore show little or no difference under the low and high emissions scenarios.

Source: SARDI (2010)

Adelaide and Mount Lofty Ranges



Alinytjara Wilurara



Eyre Peninsula



Kangaroo Island



Northern and Yorke



SA Arid Lands



SA Murray–Darling Basin



South East



Despite a decline in average rainfall, there may be an increase in flood risk due to an increase in extreme rainfall events, driven by a warmer, wetter atmosphere and warmer oceans around Australia (CSIRO 2011). This may particularly occur during wetter phases of natural variability, such as La Niña events, as seen with record rainfall falling across south-eastern Australia over the past two years, coinciding with strong, record-breaking La Niña events (Darren Ray, Senior Meteorologist/Climatologist, South Australian Regional Climate Services Centre, Bureau of Meteorology, pers. comm., 24 April 2010). This rainfall was unusual because it fell during spring and summer, rather than the normal southern rainfall season.

2.5 Observed and projected impacts of climate change

We are already seeing changes in both marine and terrestrial ecosystems due to climate change. We are starting to see impacts in human agriculture and health, and impacts on infrastructure and water supplies will increase.

2.5.1 Impacts on oceans and marine ecosystems

The world’s oceans slow the rate of warming in the atmosphere. More than 90% of the extra heat energy stored by the planet over the past 50 years has been absorbed in the ocean, causing them to expand and rise (ACE CRC 2011). The increasing heat content of the oceans and sea level rise provide further measurable evidence of the warming of the planet (CSIRO 2011). Oceans have also absorbed about 30% of the CO2 released by human activities during this time, increasing their acidity. Further acidification could have profound effects on organisms that form carbonate shells, such as corals and plankton. These organisms are a critical part of the marine food chain (CSIRO 2011).

Ocean currents are changing as a result of altered patterns of salinity (related to increased evaporation, ice melt and changing rainfall), ocean temperature and winds. Ocean currents are a key component in the distribution of heat around the planet (CSIRO 2011). The Southern Ocean plays a critical role in the global climate system and carbon cycle, because of the unique ocean currents in this region. Vast amounts of heat and about 40% of the total global ocean uptake of anthropogenic CO2 are absorbed by the Southern Ocean. The Southern Ocean also influences weather patterns over southern Australia. Observations indicate that the Southern Ocean is warming, and becoming less saline and more acidic, while ocean currents are changing (ACE CRC 2011).

Climate change represents a significant risk to the sustainability of ecosystems, fisheries and aquaculture in Australia; however, potential impacts are complex and still largely unknown. In addition to altered ocean temperature, currents, rainfall, winds and chemistry, changes in the nutrient supply (provided by the ocean circulation), altered river run-off into the coastal environment and an increase in extreme events (such as floods and storms) will significantly affect marine life. Australia’s marine environment is diverse, with many specialised environments, and the impacts of climate change will differ among them (Hobday et al. 2008).

Projected climate change impacts on South Australia’s highly diverse marine environments are likely to be large and negative. Seamounts and inverse estuaries (where the water is more saline than the open ocean, such as the Spencer Gulf) could be subjected to corrosive waters that will preclude or reduce the occurrence of many calcareous species, such as molluscs, and the larval stages of all commercial species. Increases in ocean temperature are causing the range of several species of kelp to contract southwards, and in some cases these species are disappearing altogether from coastal waters close to Adelaide. The combined impact of ocean warming and acidification on kelp is predicted to be profound. The Great Australian Bight is a region of high marine and coastal biodiversity, and many species will be affected by the projected weakening of ocean currents and increased ocean temperatures. The endemic Australian sea lion, 80% of the population of which occurs in South Australia, is a non-migratory animal that is at high risk from climate change as a result of reduced food availability and increased risk of disease, due to rising temperatures and habitat disruption. The leafy sea dragon, South Australia’s marine emblem, is likely to suffer from storm events and habitat degradation caused by ocean warming, acidification and sea level rise (NCCARF 2011, Pecl et al. 2011).

A risk assessment of South Australia’s 10 most valuable wild fishery and aquaculture species has indicated that 4 of these (southern rock lobster, blacklip and greenlip abalone, and King George whiting) are at high risk from potential climate change impacts. The South Australian coastline has two gulfs, which are zones of upwelling. Upwelling brings nutrients from the deep ocean to shallower waters, providing food for marine ecosystems. Effects of climate change on the marine environment may lead to changes in the frequency and intensity of upwelling events, potentially affecting food availability for southern bluefin tuna and the abundance of sardines. Other stressors, such as overfishing, pollution, habitat loss and disease, are likely to exacerbate the threat from climate change (Pecl et al. 2011). Increased sea water temperatures are expected to increase competition from marine pests to the detriment of native species.

Recent evidence of deaths of fish and marine mammals, and reductions in numbers of regional species, including the giant cuttlefish, seem to be in the short term connected to low oxygen levels from excessive algal blooms caused by high sea water temperature, and could be related in the long term to climate change drivers. There are insufficient data at this time to draw more definite conclusions about the causes.

2.5.2 Impacts on terrestrial plants and animals

Australia and South Australia both have rich species diversity, with many species unique to the continent. Biodiversity is a critical part of our life-support system. It provides us with fresh water, regulation of air and water quality, climate regulation, erosion control, and pest control and pollination services, as well as genetic resources for medicines, food, fibre and fuel (Steffen et al. 2009). Terrestrial biodiversity also has intrinsic, heritage and ethical values. Maintaining biodiversity and healthy ecosystems is important to assist adaptation in other sectors, such as coastal wetlands that protect human infrastructure from storm surges (Hughes et al. 2010).

Climate change will have both direct and indirect impacts on species. Increasing atmospheric CO2 concentrations can directly affect important physiological processes, such as photosynthesis, plant growth, water-use efficiency and decomposition. Indirectly, climate change acts on species through increasing temperatures, altered patterns of precipitation, and changes in the frequency and severity of extreme events (Steffen et al. 2009). Different responses by species to climate change will result in changes in the structure and composition of many ecological communities and ecosystems (Hughes et al. 2010). Indirect effects from climate change also include disturbance of predator–prey relationships.

Ecosystems are responding in a consistent way to a warming Earth, with observed changes in gene pools, species ranges, timing of biological events and ecosystem dynamics (Climate Commission 2011b). Australian and global observations show that significant impacts are already under way with only a modest amount of warming. Examples include the migration of several bird species to higher altitudes or latitudes, changing fire regimes in southern Australia and the earlier flowering of flora such as the South Australian donkey orchid (TREND 2010). Climate change is exacerbating existing threats to biodiversity from vegetation clearing, introduced species, highly modified and overcommitted water resources, fertiliser and chemical use, urbanisation, agriculture and mining (Steffen et al. 2009).

Both the magnitude and rate of future climate change pose a threat akin to past geological mass-extinction events, with a high risk of an accelerating wave of extinctions this century and beyond (Steffen et al. 2009).

2.5.3 Impacts on human health, infrastructure, agriculture and forestry

Climate change affects human health directly through a rise in extreme events such as heatwaves, bushfires, floods and storms. Indirectly, it affects human health through impacts on natural systems on which we rely and through social, economic and demographic disruptions (CSIRO 2011).

Average temperature increases of 1–2 °C can lead to a disproportionately large increase in the frequency and intensity of extreme weather events. The number of high temperature extremes in Australia has increased significantly over the past decade (Climate Commission 2011b). In March 2008, Adelaide set a heatwave record for an Australian city, with 15 consecutive days of temperatures above 35 °C, and recorded its hottest night in January 2009 during another exceptional heatwave (BoM 2009, DCCEE 2012a). The intensity of the 2009 event—with four consecutive days over 43 °C, accompanied by unusually hot nights—has been linked to a steep increase in mortality from both renal and ischemic heart disease (Nitschke et al. 2011).

Human health is predicted to be adversely affected by the spread of mosquito-borne infectious diseases such as dengue fever, malaria and Ross River virus infection (Doctors for the Environment Australia 2011). The combination of a greater number of extremely hot days and drier conditions in South Australia increases bushfire frequency and intensity, resulting in human fatalities, injuries and burns, and loss of buildings and infrastructure (Climate Commission 2011a).

In addition to the potential damage from extreme events such as bushfire, storms and floods, built infrastructure is at risk from higher temperatures, changed rainfall regimes, altered groundwater and soil conditions, and sea level rise (CSIRO 2011).

Infrastructure impacts are predicted to include:

  • increased flooding due to rainfall events that exceed the capacity of stormwater and drainage infrastructure
  • structural damage due to increased wind speed and hail intensity during storms
  • exacerbated coastal erosion, coastal inundation and damage to coastal infrastructure, including stormwater infrastructure and roads, due to more intense and frequent storm surges
  • degradation of road and building materials, and damage to building foundations and gas and water piping caused by higher temperatures, increased flooding and bushfires
  • rail buckling and signal failure, and road fatigue, due to increased temperatures
  • power disruptions from surges in electricity demand caused by more frequent heatwaves (Engineers Australia 2010).

With most of Australia’s settlements in the coastal region, sea level rise presents a widespread risk of inundation and damage to a significant stock of residential housing, commercial buildings and infrastructure, such as ports, roads and railways. Mean sea level rise may lead to eventual permanent inundation of low-lying areas. Sea level rise (combined with more storminess as a result of climate change) will also contribute to extreme short-term coastal inundation events, which may become increasingly severe and frequent in many coastal places. Coastal environments such as beaches, estuaries, wetlands and low-lying islands are at risk of salinisation and inundation in the coming decades. In South Australia, up to 43 000 residential buildings, with a value of $7.4 billion, and 1500 commercial buildings valued at $27 billion have been identified as at risk of inundation (DCCEE 2009).

Increased temperatures, reduced rainfall and more frequent extreme weather events are expected to reduce crop and livestock production in South Australia. Since 1997, South Australia’s agricultural regions have experienced a marked decline in growing season rainfall. Forestry and plantation industries are at greater risk from bushfire (CSIRO 2011, DCCEE 2012a). Viticulture is sensitive to climate change on a number of fronts, including changes in mean temperature, extreme temperatures, rainfall, the quality and quantity of water available for irrigation, and the atmospheric concentrations of greenhouse gases (Hayman et al. 2009).

Reduced rainfall and higher rates of evaporation are expected to significantly reduce the reliability of South Australia’s water supply, resulting in less water being available for irrigation, domestic use and industry (CSIRO 2011).

Moon over eroded mesas near the Painted Hills, Woomera Prohibited Area

Angus Kennedy

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