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Chapter 2 Science and impacts of climate change

There is no doubt that the climate has been warming since the 19th century. It is extremely likely 1 that humans have been the dominant cause of the observed warming since the 1950s due to greenhouse gas emissions from activities such as the burning of fossil fuels.

Increases in greenhouse gas concentrations and global surface temperature are occurring much more rapidly than at previous times in the Earth’s history. This is affecting weather, human settlements, agriculture, water resources and ecosystems.

The international community has committed to limiting global warming to below 2 degrees. This will not avoid impacts – humans and the natural environment will still experience more frequent extreme weather events, changes to the distribution of rainfall and changes in the habitat range for particular species. However, if the world limits warming to no more than 2 degrees, Australia is likely to be capable of adapting to many of the projected impacts. Above 2 degrees, many regions, environmental and economic sectors will face increasingly significant challenges and adaptation may not be possible.

If emissions continue to grow at current rates, warming is projected to increase rapidly over the 21st century, exceeding 2 degrees within the next few decades, and foreseeably reaching 4 degrees or more by the end of the century. Higher temperatures are projected to bring more severe impacts, including inundation of low-lying coastal areas, climate-induced migration of millions of people, growing risks to human health from many sources, and the collapse of many vulnerable ecosystems including the Great Barrier Reef and the Kakadu wetlands. Temperature increases above 2 degrees also heighten the risks of triggering several highly disruptive climate feedbacks, which could amplify the initial warming caused by greenhouse gases and increase the severity of climate change impacts. These impacts would be highly disruptive, impose a heavy financial burden and, in many cases, would prove to be beyond Australia’s capacity to adapt.

Australia has a clear national interest in limiting global warming to no more than 2 degrees.

This chapter provides the essential context for this Review, and why Australia and the world must take action to limit global warming. The scientific reality is that climate change is taking place, and that humans are having a clear influence on the climate system – greenhouse gas concentrations have grown at rapid rates since the 1950s, more energy has been trapped within the Earth’s system, temperatures have increased and scientific understanding of the climate system has advanced (IPCC 2013a, p. 10). These developments are comprehensively discussed in the latest Intergovernmental Panel on Climate Change (IPCC) 2013 report on the physical science basis of climate change, which is the pre-eminent source of peer-reviewed science assessing climate change.

Despite the compelling scientific evidence, coverage of the science can at times be misrepresentative and confusing, focusing on moment-in-time detail, rather than long-term trends. Long-term trends will ultimately determine the magnitude of impacts from a warming climate and their effects on future generations, and are the most appropriate guide for policy-makers. This Review uses the scientific consensus on climate change as its foundation, and takes the warnings it has been sounding over many years very seriously.

Box 2.1: Background to the IPCC Fifth Assessment Report

The IPCC is a scientific body under the auspices of the United Nations and the leading international body for the assessment of climate change. It reviews, assesses and synthesises the most recent peer-reviewed scientific, technical and socio-economic literature on the status of climate change produced worldwide. The IPCC has a comprehensive review process to ensure assessments are objective and thousands of scientists contribute to it globally.

The first working group report of the IPCC’s 2013 Fifth Assessment Report reinforces a message which has been consistent since the IPCC’s First Assessment Report in 1990, almost 25 years ago – human activities are heating up the planet. The 2013 report again confirms the projected long-term trends attributable to increased greenhouse gas concentrations, with strengthened confidence and scientific understanding based on a vast body of evidence accumulated over many years.

Climate change is already affecting human settlements and ecosystems in a range of damaging and disruptive ways, which will extend and worsen with increasing temperatures. To reduce the risk of encountering increasingly severe impacts, the world needs to make substantial and continued efforts to reduce greenhouse gas emissions, consistent with limiting warming to no more than 2 degrees. The scale of this global challenge is described in Chapter 3, which outlines what is required at a global level to give a reasonable chance of limiting warming to below 2 degrees. Chapter 9 discusses the national challenge and what Australia’s fair share of the global emissions reduction task may be.

Specifically, this chapter discusses:

  • the relationship between greenhouse gases and global warming;
  • climate science modelling and risks;
  • the impacts from climate change observed to date; and
  • the projected impacts of climate change, both globally and in Australia.

2.1 Climate change science

2.1.1 The relationship between greenhouse gases and temperature

There is no doubt that the climate has been warming since the 19th century. The main cause is the increase in concentrations of greenhouse gases (and especially carbon dioxide), which have been growing since industrialisation, primarily as a result of human activities.

The connection between greenhouse gas concentrations in the atmosphere and the warming of the climate was made more than a century ago (IPCC 2007a, p. 103). Greenhouse gases trap and re-emit radiant heat in the atmosphere, which warms the Earth’s surface and climate through what is commonly called the greenhouse effect. The primary greenhouse gases are carbon dioxide, methane, nitrous oxide, water vapour and ozone; additional greenhouse gases are covered under the Kyoto Protocol2. Carbon dioxide is the most important – it is produced in large quantities by human activities, is in the highest concentration of all the greenhouse gases and is very long-lived: about one-third of the carbon dioxide increase due to emissions this year will remain in the atmosphere in 100 years, and about 20 per cent will still be present in 1 000 years. This means that carbon dioxide emissions continue to affect the climate long after they are released.

The record of the distant past confirms current observations that increasing greenhouse gas concentrations have a warming effect on the climate. The historical record has been established by samples of ice cores, which provide 800 000 years of information regarding the composition of the gases in the atmosphere (trapped in bubbles within the ice) and temperatures over time (IPCC 2013a, p. 7). Additional information on the climate of the past has been obtained from deep sea sediments and geological formations and fossils, which extend our understanding of the Earth’s climate to millions of years ago.

Since 1750 and the beginning of the Industrial Revolution, human activities, primarily the burning of fossil fuels and deforestation, have dramatically increased the amount of carbon dioxide in the atmosphere (by 40 per cent), as well as methane (by 150 per cent) and nitrous oxide (by 20 per cent) (IPCC 2013a, p. 7). Based on ice core records, current concentrations of these three greenhouse gases substantially exceed the concentrations which existed over the last 800 000 years (IPCC 2013a, p. 7).

It is extremely likely that most of the warming observed since the 1950s has been caused by increases in greenhouse gas concentrations that have been produced from human activities (IPCC 2013a, p. 12). This assessment is supported by very strong scientific consensus that climate change has been caused by human activities – from a study of almost 12 000 peer–reviewed journal article abstracts published between 1991 and 2011 which mention anthropogenic global warming, more than 97 per cent endorsed this conclusion (Cook et al. 2013).

Figure 2.1 charts the level of carbon dioxide, methane and nitrous oxide over the past 1 000 years, showing rapid increases in concentrations in all three major greenhouse gases, particularly since the 1950s.

Figure 2.1: Carbon dioxide, methane and nitrous oxide concentrations over the past 1 000 years

Source: Adapted from CSIRO 2012, p. 8

While all greenhouse gases have a warming effect, other agents in the atmosphere can have either a cooling or warming influence. The most widely discussed are aerosols, tiny airborne particles such as soot produced from burning fossil fuels, that remain in the atmosphere for a few hours to a few weeks. Aerosols produced by human activities have a net cooling influence on the global climate, and currently mask the warming influence of all non-carbon dioxide greenhouse gases. The cooling effect of aerosols is expected to decline over coming decades as countries implement pollution reduction policies.

2.1.2 Is the current warming unusual?

Measurements from the recent past (going back more than a hundred years) confirm that both temperatures on Earth and greenhouse gas concentrations have been increasing. Despite the Earth’s history of climate variability, the level of current carbon dioxide concentrations is unprecedented for at least 800 000 years (IPCC 2013a, p. 7). Warming is also occurring much more rapidly, at rates which are very unusual compared with climate in the past (IPCC 2007a, p. 465). It is highly likely that temperature changes will intensify over coming decades, increasing at a rate at least 10 times faster than any climatic shift over the past 65 million years (Diffenbaugh et al. 2013). A recent reconstruction of global temperatures spanning the last 11 300 years – roughly the time span of developed human civilizations – found that the decade from 2000–2009 was warmer than 75 per cent of all temperatures during the same period, and that the projections for global temperatures to 2100 under various emissions scenarios exceed the range of temperatures ever experienced by modern humans (Marcott et al. 2013).

Box 2.2: Has global warming ‘paused’?

While the long-term trend of a warming climate remains, the warming trend between 1998 and 2012 in global average surface temperature was lower than the average trend over the period 1950–2012 (IPCC 2013a, pp. 3, 10). The lower rate of warming observed over the past 15 years is explained by natural variability, including volcanic eruptions which increased the volume of cooling aerosols in the stratosphere, as well as redistribution of heat within the ocean (IPCC 2013a, pp. 9–10).

This relatively short-term variability does not change the long-term trends of a warming climate – average surface temperatures over land and oceans have been successively warmer in each of the last three decades compared with any preceding decade since 1850, and the first decade of the 2000s was the warmest on record. Many other climate indicators confirm the ongoing warming influence of higher concentrations of greenhouse gases – from the 1990s to the present, sea levels have continued to rise, warming is occurring at greater depths of the ocean and ice sheets have been melting at greater rates, compared to earlier periods.

2.1.3 Climate models

Climate models also support the evidence of a warming climate. Climate models are based on physical laws and representations of the climate system, including the atmosphere, land, oceans, carbon cycles and climate. There is a high degree of confidence in the ability of climate models to simulate changes such as large-scale temperature changes, the more rapid warming which has occurred since the 1950s, seasonal Arctic sea ice extent and the global distribution of temperature extremes (IPCC 2013b, ch. 9, pp. 3–4). This confidence is a result of comparing actual observations of past climate with model simulations on a regular basis. The future extent of climate change cannot be predicted with certainty because there are several unknowns, such as the level of emissions from human activities and the precise temperature response to concentrations of greenhouse gases. Despite this, extensive testing provides confidence that climate models represent the best tools for estimating future climate change (CSIRO 2013a).

2.1.4 Uncertainties and risks of a warming climate

One of the factors that will determine future temperature is the way in which carbon dioxide emissions are taken up within the Earth’s system. Carbon dioxide emissions can dissolve in the ocean, be taken up by plants and other vegetation through photosynthesis or remain in the atmosphere. So far, about 55 per cent of carbon dioxide emissions from fossil fuel combustion have been absorbed by the land and oceans combined, with the rest remaining in the atmosphere, which is where the greenhouse effect takes place. But there is evidence that the ocean has become less effective at absorbing carbon dioxide emissions over the past 50 years (Canadell et al. 2007). Although trees and vegetation have been increasing the amount of carbon dioxide removed through photosynthesis, this trend is expected to peak and decline by the middle of the 21st century under current rates of emissions (IPCC 2007b, p. 213).

This is due to plants reaching their maximum rates of photosynthesis and higher rates of decay of dead organic matter (which releases greenhouse gases). There is also projected dieback of some forests due to changes in precipitation and temperature, notably in the Amazon rainforest (IPCC 2007b, pp. 221–222). The weakening capacity of the land and oceans to absorb carbon dioxide means that more emissions are expected to remain in the atmosphere in the future, which would increase the warming trend.

A substantial risk in the future level of climate change relates to uncertainty in the timing and temperature at which some very disruptive climate feedbacks will be triggered. Climate feedbacks are climate-related processes that can have positive or negative impacts on temperature change, depending on whether they amplify or negate the current increase in temperature. Positive climate feedbacks are particularly concerning because they may drive additional warming. There are many significant positive feedbacks which could occur. One example is the potential large-scale melting of permafrost, which is perennially frozen ground that stores carbon in the form of organic matter (Tarnocai et al. 2009). If permafrost melts on a large scale, the organic material will decay, releasing unknown quantities of carbon dioxide and methane over centuries that could amplify the greenhouse effect.

Higher levels of warming also increase the likelihood that the climate system will reach a tipping point that results in an abrupt and irreversible change to the climate system. Examples of tipping points include permanent melting of the Greenland and West Antarctic ice sheets. This could be triggered before the end of the 21st century under higher levels of warming and create continuously rising seas for centuries or millennia – there is enough ice contained in the West Antarctic ice sheet to increase global average sea levels by about six metres under complete melting, while Greenland’s ice sheet could increase sea levels by an additional seven metres (Richardson et al. 2011, ch. 3.5.2). Another tipping point would be a permanent shift in the strength and location of the Indian summer monsoon, which could endanger the production of food for more than a billion people (Lenton et al. 2008, Table 1).

Current scientific understanding indicates that thresholds for setting off most of these high-risk climate system processes are unlikely to lie below 2 degrees of warming (Lenton et al. 2008, Table 1). An important exception is the irreversible melting of Arctic summer sea ice and the Greenland ice sheet, which could be triggered under average global warming of between 1 and 2.5 degrees, as temperature increases in the Northern Hemisphere are higher than the global average (Lenton et al. 2008, Table 13).

The precise temperature thresholds of some disruptive feedbacks and tipping points are not known with certainty, but they could result in very severe outcomes. It is clear that action should be taken to avoid the risk of triggering them wherever possible.

2.2 Climate change impacts

In 2009, the international community agreed to a global goal to limit average temperature increases to below 2 degrees (Copenhagen Accord 2009). This does not mean that significant impacts from climate change do not occur below 2 degrees. Emerging evidence indicates that climate change impacts at lower temperatures are larger and more damaging than previously estimated, and that changes in the climate system are occurring more rapidly than expected (IPCC 2007b, 19.3.7; Smith et al. 2009). Small island states are particularly vulnerable to sea level rise, storm surges and ocean acidification, and are among those that do not accept 2 degrees as a sufficient upper limit to prevent dangerous climate change impacts. The international community has agreed to conclude a review in 2015 of whether the 2 degree goal should be strengthened to a 1.5 degree limit.

Current and projected impacts of climate change are discussed below. These clearly demonstrate Australia’s interest in limiting global warming to 2 degrees or below.

2.2.1 Temperature rise and observed impacts to date

Between 1880 and 2012, average global surface temperatures over land and the ocean have warmed by 0.85 degrees (IPCC 2013a, p. 3). Each of the last three decades has been successively warmer than any preceding decade since 1850 (IPCC 2013a, p. 3). This average conceals substantial regional variations, with higher levels of warming at northern latitudes in particular – average Arctic temperatures have increased at twice the global average over the past century, and the three decades to 2012 were likely the warmest 30-year period in the Northern Hemisphere for the last 1 400 years (IPCC 2007b, p. 30; IPCC 2013a, p. 3).

In Australia, average daily temperatures have warmed by 0.9 degrees and average nightly temperatures have warmed 1.1 degrees since 1910 (CSIRO 2012, pp. 3–4). Figure 2.2 charts the difference in Australian average annual temperatures (orange line) and smoothed trend (black line) against the 1961–1990 average temperature. Decade average deviations from the 1961–1990 average are shown in the grey boxes. Despite annual variability, every decade has been warmer than the previous one since the 1980’s.

Figure 2.2: Average temperatures in Australia over the past century

figure 2.2

Source: CSIRO 2012, p. 3
Note: *11-year average is the standard used by the IPCC.

The world’s oceans have also been warming, absorbing about 90 per cent of the additional heat within the Earth’s system (IPCC 2013a, p. 4). The increase in ocean heat content since the 1960s is shown in Figure 2.3. Temperatures have increased most at the sea’s surface and upper ocean (to 700 metres below), where 60 per cent of the net increase in energy within the climate system has been stored (IPCC 2013a, p. 5). In Australia, sea surface temperatures have warmed by about 0.8 degrees since 1910, which is faster than the global average. In 2010, sea surface temperatures in Australia were the highest on record (CSIRO 2012, p. 7).

Figure 2.3 Changes in ocean heat content since 1960

figure 2.3

Source: CSIRO 2012, p. 7
Note: Ocean heat content is relative to 1970 levels. Shading provides an indication of the accuracy of the estimate.

Oceans take a long time to warm in response to additional heat in the atmosphere. This thermal inertia means the world will continue to warm even if fossil fuel burning stops today. If greenhouse gas concentrations and other atmospheric constituents such as aerosols had been held at 2000 levels, an additional 0.6 degrees of warming would still occur by the end of the 21st century (IPCC 2007a, 10.7.1). Together with 0.8 degrees of warming observed to 2000, the total warming that would be expected to occur from emissions to 2000 would be 1.4 degrees (IPCC 2007a, SPM). Additional emissions from human activities will mean that humans will commit the climate to further warming.

Sea water expands as it warms, which contributes to a rise in global sea levels – thermal expansion of the oceans has contributed 40 per cent of observed sea level rises since 1971, and is projected to make the largest contribution to sea level rise in centuries to come (IPCC 2013b, Table 13.1). Between 1901 and 2010, global average sea levels rose by 0.19 metres (IPCC 2013a, p. 6). As with temperature, the average hides variation across different locations. Since 1993, the rate of sea level rise to the north and northwest of Australia has been 7–11 millimetres per year, more than double the 1993–2011 global average (CSIRO 2012, p. 6). Central east and southern coasts of Australia have been closer to the global average (CSIRO 2012, p. 6; IPCC 2013a, p. 6).

The loss of mass from glaciers and ice caps, and the melting of large polar ice sheets on Greenland and Antarctica, have been making a greater contribution to sea level rise in recent decades. Since the 1990s, these major ice sheets have shifted to a state of losing ice (about 4 000 billion tonnes combined between 1992 and 2011), and at an accelerating pace (Shepherd et al. 2012; IPCC 2013b, Table 13.1). Other dramatic changes have been observed in the Earth’s ice and snow coverage, which play a very important part in moderating the climate system. There has been a sharp decline in Arctic summer sea ice extent since the 1950s, which reached a record low in the Northern Hemisphere summer of 2012 (IPCC 2007b, p. 83; NSIDC 2012). The melting of ice also exposes darker water and landscapes, which absorb more solar radiation and amplify warming (Lenton 2008, p. 3). In recent years, glaciers have retreated world-wide, Northern Hemisphere snow cover in spring has declined and substantial thawing of permafrost has occurred, particularly in Russia (IPCC 2013b, ch. 4, pp. 4–5).

Many other observations of climate system changes have been recorded, including changes in rainfall and increased frequency of extreme weather events (see Box 2.3). In south-west Western Australia, average winter rainfall has declined by 20 per cent since the 1960s, and scientists have attributed half of this impact to climate change (Cai and Cowan 2006). Warmer temperatures have also been shown to affect the timing of plant and animal life cycles and the range in which plants and animals live, while heat stress from more frequent and longer duration heatwaves has resulted in mortality of humans, plants, animals and coral reefs (IPCC 2007b; Smith et al. 2009; Climate Commission 2013).

Box 2.3: Extreme heat events

The atmosphere and oceans have changed as a result of more heat being trapped within the atmosphere. These changes affect storms and extreme climate events – but it can be difficult to discern those effects from natural climate variability. One approach to detecting the influence of climate change is to look for long-term changes in mean climate conditions – a small shift in the average can result in very large percentage changes in the extremes (Trenberth 2012).

Figure 2.4: The relationship between climate averages and extremes

Source: Modified from Climate Commission 2013b

As shown in Figure 2.4, an increase in average temperatures can have a large effect on the frequency and extent of extreme hot weather (Climate Commission 2013b). In Australia, this pattern is becoming more apparent. Average temperature in Australia has increased by 0.9 degrees since 1910 and, as predicted, there has been a significant increase in the number of hot days (over 35 degrees) and hot nights, and a general decrease in the number of cold days and nights. The 2012–13 Australian summer was Australia’s hottest since records began, with more than 80 heat-related records set in January 2013 alone, including the hottest day on record (BoM 2013).

Over the past decade, many other countries and regions have experienced periods of extreme heat, including severe heatwaves in India (2002 and 2003), Europe (2003) and various parts of China (2010) (WMO 2011, p. 5). The 2010 Russian heatwave was of particular note, not only for its intensity and resulting death toll of over 55 000 people (CRED 2011), but also for demonstrating another linkage between climate change and extreme weather. The loss of Arctic sea ice resulting from increased air and ocean temperatures has been linked to changes in the polar jet stream – the river of high–altitude air that works to separate Arctic weather from that of northern Europe, Russia and Canada. There is now growing evidence that aberrations in jet streams contributed to various recent extreme weather events, including the record-breaking Russian heatwave (2011), the wet summer and autumn in the United Kingdom and Ireland (2012), the blocking of Hurricane Sandy’s trajectory (which subsequently hit New York in 2012) and the recent historic floods in Central Europe (2013).

Many climate change impacts could impose high financial costs in the form of damage to infrastructure and buildings affected by extreme weather events and rising sea levels, reduced tourism revenue from damaged or less appealing attractions (such as bleached coral reefs) and reduced agricultural production and stock loss in the event of drought and floods. There are also likely to be substantial impacts that are hard to value in dollar terms, such as the damage or collapse of vulnerable ecosystems, reduction in biodiversity and mental health consequences of more frequent drought and flood (Bambrick et al. 2008).

Box 2.4 describes some of the attempts to estimate the cost of climate change impacts and provides some examples of the costs of extreme weather events that have occurred in the recent past – and are projected to occur more frequently under a warming climate.

Box 2.4: Estimating the cost of climate change impacts

Attempts to quantify the cost of climate change impacts were made in both the Stern (2006) and Garnaut (2008) reviews. Stern addressed the question of whether global mitigation benefits outweighed the costs of climate change impacts for the world as a whole, while Garnaut focused on the benefits and costs of Australia contributing to the global mitigation effort.

Garnaut noted that it is only possible to quantify some of the costs of projected climate change impacts, namely where there is a market effect and available data, such as the loss of gross domestic product (GDP) due to declining agricultural productivity or reduced tourism. Other costs associated with climate change impacts are harder to quantify, as they require valuation of non-market goods, such as society’s willingness to pay to avoid a small probability of catastrophic damage, or the value that Australians place on maintaining the integrity of its environmental assets, such as the Great Barrier Reef. Garnaut also highlighted the challenge of directly assessing the effect of Australian mitigation on the impacts of climate change because the task of reducing emissions is a global one.

Despite the challenges of estimating costs of climate change impacts, and the omission of quantitative estimates for a significant proportion of non-market impacts, both Stern and Garnaut came to broadly similar conclusions – that the cost of unmitigated climate change will exceed the costs of mitigating it.

While estimating the global or national costs of climate change impacts remains an extremely difficult task, it is possible to look at the historical cost of events likely to occur more frequently in the future due to climate change. For example, there is a clear link between the intensity and frequency of extreme weather events and climate change (discussed in Box 2.3). Australians have witnessed several extreme weather events in the last decade that have incurred substantial economic costs. The ‘millennium drought’ of 1997–2009 was the most severe Australian drought on record, and resulted in substantial declines in agricultural production in south-east Australia, affecting both crops and stock (CSIRO 2010). In 2006–07, the net value of farm production fell 74 per cent ($5.4 billion) on the previous year alone (DAFF 2010). In addition to the loss of 173 human lives, the economic costs of the 2009 Victorian Black Saturday bushfires were estimated to be in excess of $4 billion (Royal Commission 2010). The 2011 Queensland floods caused the loss of 35 lives and were estimated by the Office of the Queensland Chief Scientist to have cost the state between $5 and $6 billion. The 2011 Review of the 2010–11 Victorian floods estimated costs up to $1.3 billion. The economic, environmental and human cost of more frequent and intense extreme weather events is likely to be significant in the future.

Sea level rise could also result in substantial economic costs. Some of Australia’s most economically, socially and culturally valuable property is in the coastal zone (CSIRO 2013b). Sea levels are projected to rise 0.43–0.73 metres by 2100 (best estimate), compared with the average sea level for 1986 – 2005 (IPCC 2013b, Table 13.5). This could lead to coastal inundation of tens or even hundreds of metres inland, depending on local topography. It is virtually certain that global average sea levels will continue to rise after 2100, which would further increase the risks to human settlements (IPCC 2013b, ch. 13, p. 4). For Australia, if sea levels rose by 1.1 metres, approximately $226 billion in capital assets would be exposed (DCCEE 2011). Across the country, some local and state governments are acting to address the expected impacts from sea level rise, but progress is highly varied.

2.2.2 Projected global impacts

Climate change is projected to affect different regions in different ways, depending on the level of temperature rise, shifts in weather systems, and the vulnerability of different ecosystems and human populations to changing climate conditions.

Figure 2.5 depicts the types of global impacts which are projected at different levels of warming above pre-industrial levels, showing considerable impacts even for temperature changes below 2 degrees. Higher temperatures are projected to have more severe impacts, including extensive melting of ice, higher sea levels leading to coastal inundation, far greater water scarcity in many regions and irreversible loss of biodiversity, including coral reef systems (World Bank 2012, p. ix). As discussed in Section 2.1, there is also the potential to pass thresholds for disruptive feedbacks and tipping points.

Some of the key projected global impacts include:

  • Across the world, dry regions are generally projected to become drier (through increased evaporation) and wet regions are projected to become wetter (through increased rain) (IPCC 2007a). Extreme weather events such as heatwaves, droughts, storms, floods and wildfires are projected to become more frequent and more intense for some locations – with 4 degrees of warming, the most extraordinary heatwaves experienced today will become the new norm and a new class of heatwaves, of magnitudes never experienced before, will occur regularly (Schaeffer et al. 2013, p. 15).
  • Glaciers, ice sheets and polar ice are projected to melt and sea levels to continue to rise, with increasing risks of flooding, coastal erosion and salt contamination of fresh water. The most recent IPCC (2013a) science report projects higher sea level rises than previous reports, and with greater confidence. Under the lowest emissions scenario (which require large and rapid cuts to global emissions), sea levels in 2100 are estimated to be 0.43 metres higher (with a likely range of 0.28–0.6 metres) compared with the average sea level between 1986 and 2005. For the IPCC’s high emissions scenario, sea level rise is projected to be around 0.73 metres (with a likely range of 0. 53–0.97 metres) (IPCC 2013b, Table 13.5). Sea level rise will exacerbate the effects of coastal flooding because higher sea levels mean that large waves produced by storm surges will be taller and could reach further inland (Climate Commission 2013, p. 58). Projected sea level rise could flood low-lying islands and densely populated delta areas in countries such as Bangladesh, India, Vietnam and China, with potentially severe consequences for infrastructure, human settlements, transportation, tourism, livelihoods and insurance costs (IPCC 2007b, ch. 10.4.3). For example, the projected minimum sea level rise in Asia of 40 centimetres over the course of this century is projected to increase the number of people in coastal populations flooded each year from 13 million to 94 million (IPCC 2007b, ch. 10.4.3). As temperatures and sea levels continue to rise, these risks will increase.
  • Ecosystems are projected to experience major changes in structure and function under climate change, with 20 to 30 per cent of assessed plant and animal species at increased risk of extinction for an average temperature increase of 2 to 3 degrees, and 40 to 70 per cent of assessed species committed to extinction above 4 degrees (IPCC 2007b, pp. 38, 242). Particularly vulnerable ecosystems include coral reefs (due to ocean acidification and coral bleaching), Arctic and alpine ecosystems and tropical forests (including the Amazon rainforest). Projected losses of individual species are also likely to have serious ramifications across entire interlinked ecosystems which are more difficult to predict. The resilience of many ecosystems is likely4 to be exceeded this century due to climate change and associated impacts such as flood, drought, ocean acidification and invasive species, combined with other stressors such as deforestation and pollution (IPCC 2007b, p. 11).
  • Continued increases in atmospheric concentrations of carbon dioxide will lead to further global increases in ocean acidification (IPCC 2013a, p. 19). Increasing acidification is likely to have adverse impacts on some marine ecosystems, such as coral reefs.
  • Impacts on human populations include, at the extreme, far greater loss of life from a variety of causes linked to rising temperatures. Damage to infrastructure and private property due to extreme events, reduction in agricultural productivity and displacement by rising sea levels are also projected to have global ramifications. Climate-induced migration could create humanitarian crises and cause or exacerbate ethnic, political and international conflict and even terrorism (Australian Government 2013, p. 18). One study has estimated that, under a high emissions scenario with one metre of sea level rise in the 21st century, up to 187 million people could experience forced displacement (Schaeffer et al. 2013, p. 17)
  • Human health effects from climate change will have many sources. The risk of exposure to higher temperatures, particularly among vulnerable populations, is well understood – for example, the European heatwave of 2003 is estimated to have resulted in an additional 1 000 deaths over several days in Paris alone (McMichael 2014, pp. 156–7). Climate change is also projected to create more areas with a suitable climate for the transmission of pathogen and vector–borne diseases, including those carried by mosquitos (McMichael and Lindgren 2011). In the developing world, climate change is projected to cause protracted impacts on human health as a result of increased malnutrition due to declines in local agricultural production. Malnutrition is projected to increase the incidence of stunted growth in children and result in higher numbers of famine–related deaths (Lloyd et al. 2011; Black et al. 2008).
  • Adaptation to impacts of climate change may be possible for several sectors and many countries under lower levels of temperature rise (up to 2 degrees). For example, agricultural crops could be switched to more drought-tolerant and disease-resistant varieties, or coastal communities threatened by sea level rise could be resettled further inland – but many of the adaptation opportunities will be costly to implement (CSIRO 2011, ch. 4).
  • Wealthier countries generally have a much greater capacity to adapt to climate change compared with developing countries, because more resources are available to put towards research and development, deploying new technologies and techniques, repairing physical damage to infrastructure and delivering health care. By comparison, developing countries such as those in Africa are considered to have weak adaptive capacity (Collier et al. 2009; IPCC 2007b, ch. 9). At 4 degrees of warming, the adaptive capacity of even wealthy countries is projected to become constrained – in Australia, almost all key sectors (including ecosystems, human health, tourism, agriculture and forestry) are projected to be vulnerable at 4 degrees (IPCC 2007b, fig. 11.4).

Figure 2.5: Global impacts projected to result from rising temperatures

Source: Adapted from IPCC 2007b, Table TS.3

2.2.3 Projected Australian impacts

Australia is the driest inhabited continent in the world, and has an inherently variable climate, including extremes of floods and droughts. Climate change is projected to exacerbate these extremes, with heatwaves, fire, floods and drought expected to become more frequent and more intense over coming decades in much of Australia, particularly in the south. Frost and snow are expected to become rarer or less intense events (CSIRO 2011, p. 46). There is evidence these changes are already occurring, with more heatwaves, fewer frosts, more rain in north-west Australia, and less rain in southern and eastern Australia in recent decades.

The future impacts of climate change in Australia will vary by location, due to differences in local climate and the vulnerability of different regions to change. The risks to Australia at 2 degrees of warming have been well established through successive IPCC Assessment Reports and other work by organisations such as the CSIRO. Australia is a wealthy country with considerable experience in adapting to challenges in our natural environment (such as floods, fire and drought), and is likely to be able to adapt to many of the impacts of a 2 degree temperature increase, with the important exception of vulnerable ecosystems (CSIRO 2011, ch. 5). But the expected changes even under low levels of warming will be unwelcome, disruptive and likely to pose heavy financial, physical and emotional burdens on governments, communities and individuals. Governments, including Australia, will also be tasked with responding to an increased demand for humanitarian assistance, disaster relief and stabilisation operations resulting from climate impacts in the region (Defence White Paper 2013).

More recently, attention has focused on the risks to Australia if current emissions trends continue and temperature increases by 4 degrees by the end of the century. As a recent work notes, ‘what emerges [under 4 degrees projections] is a disturbing and bleak vision of a continent under assault … our everyday lives will change profoundly even if adaptation succeeds’ (Christoff 2014, p. 236). Some of the projected impacts under warming of around 4 degrees are identified for various locations around Australia in Figure 2.6. From these examples it is clear that 4 degrees of warming would have far-reaching effects, with consequences for all types of people, communities and ecosystems.

The emissions produced today and into the future will determine the speed and extent of climate change over coming decades and centuries. Avoiding the most severe impacts requires substantial and sustained global action. The size of the task is described in Chapter 3, which discusses the limit on the emissions the world can release over coming decades to give a reasonable chance of limiting warming to no more than 2 degrees.

Figure 2.6: Projected impacts for Australian locations under 4 degrees of warming

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Australian alps

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Snow cover is projected to fall to zero for most regions that currently experience a significant snow season.

A snow season is projected to only persist at very high locations, but the snow season would be greatly reduced (e.g. at 2 000 metres, the snow season is reduced to one-third of its current length) (Whetton et al. 2014, p. 28).


The number of days in Adelaide above 35 degrees is projected to increase from 17 (1971–2000 average) to 47 by 2070 (under high scenario)(Braganza et al. 2014,Table 3.1, p. 48).


The average number of extreme fire danger days in Mildura is projected to increase from 79.5 days per year to 107.3 days in 2050 under a high emissions scenario (Commonwealth of Australia 2007, Table 5.7). Note: ‘present’ is the 1974–2003 average.

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South-west WA


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Southern NT, Queensland and northern NSW

Queensland in flood


Western Australian landscape



More than $50 billion in commercial, industrial, road and rail and residential assets in Queensland are potentially exposed to flooding and erosion caused if sea levels rise by 1.1 metres, making it the most at-risk state for these types of assets (DCCEE 2011, Figure 1).


Average annual rainfall in south-west Western Australia is projected to continue to decline (following the drying trend observed since the 1970s). Rainfall is projected to decrease by 20 per cent in 2070 compared with 1990 – from 747 mm (1971–2000 average) to 605 mm. Rainfall decline is expected to have a significant impact on wheat yield. Under the worst projections of extremely hot and dry climate conditions, wheat production may be abandoned in most Australian regions by 2100 (Garnaut 2008, p. 133; CSIRO and BoM, 2008).


The area of Australia with a suitable climate for dengue fever transmission is projected to expand southwards, increasing from northern and central areas of Queensland and the Northern Territory to northern New South Wales by 2100. This is projected to increase the population exposed from almost 0.5 million in 2020 to around 5–8 million in 2100 (Bambrick et al. 2008, pp. 37–38).

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Murray-Darling Basin

The Murray river



In the absence of mitigation, the value of agricultural product from the Murray-Darling Basin may decrease by 12–44 per cent in 2030 (compared to a scenario with no human-induced climate change) and 49–72 per cent in 2050, as a result of projected declines in stream flow, increases in water salinity and reduced water allocation to irrigation (Garnaut 2008, p. 130; Quiggin et al. 2008).





This figure is a map of Australia which highlights some of the projected impacts in specific Australian locations under 4 degrees of warming.  These projected impacts include: • Snow cover falling to zero for most regions in the Australian alps that currently experience a significant snow season. • An increase in the number of days in Adelaide above 35 degrees each year, from 17 (1971-2000 average) to 47 by 2070 • An increase in the average number of extreme fire danger days in Mildura from 79.5 days per year to 107.3 days in 2050 • An expansion of the area in Australia with a suitable climate for dengue fever transmission , increasing from northern and central areas of Queensland and the Northern Territory to northern New South Wales by 2100. •	A decline in the value of agricultural product from the Murray Darling Basin, which may decrease by 12-44 per cent in 2030 and 49-72 per cent in 2050, in the absence of mitigation. This is a result of projected declines in stream flow, increases in water salinity and reduced water allocation to irrigation.

Notes: Some of the impacts occur on the trajectory to 4 or more degrees by the end of the 21st century (high emissions scenario), but temperatures may be below 4 degrees when the reported impact is projected. The impact examples above (which assume 4 degrees of warming is reached or exceeded sometime within the next century) are based on climate models in which emissions continue to grow at rapid rates. A commonly used high emissions scenario (published by the IPCC in 2000) is the A1FI scenario, which assumes a future world of very rapid economic growth, global population that peaks in the middle of the 21st century and continued technological emphasis on fossil fuels (IPCC 2000).

1 ‘Extremely likely’ is defined by the IPCC as 95–100% probability.

2 The Kyoto Protocol gases are carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, sulphur hexafluoride and nitrogen trifluoride. Nitrogen trifluoride is included for the second commitment period.

3 Lenton describes warming above the 1980–1999 average. 0.5 degrees has been added to Lenton et al’s estimates for warming from the Industrial Revolution to 1980–1999.

4 66–90 per cent probability.