Climate change—a science overview

Emily Hanna, Science, Technology, Environment and Resources

Key Issue
The impacts of human-influenced changes to the climate are already occurring and are expected to continue and intensify in the future. The issue of climate change and its impacts has significant implications for government policy across a range of portfolios and industries.

Nearly 200 national and international scientific bodies, as well as over 97 per cent of recently published climate scientists, agree that the Earth is warming and that humans are contributing to the change in climate.

Global climate change

Since its first assessment in 1990, the Intergovernmental Panel on Climate Change (IPCC) has expressed growing certainty that global warming is underway and that human activity is a principal cause. In its latest report on climate change, the Fifth Assessment Report in 2014, the IPCC stated:

Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, and sea level has risen.

Globally, the average temperature (combined land and ocean surfaces) has increased 0.85 °C between 1880 and 2012, according to the IPCC. Most of this heat is stored in the oceans, with the top 75 metres of water warming an average of 0.11 °C per decade globally over the four decades until 2010.

The IPCC states that average sea level has already risen around 20 centimetres since 1901 and is forecast to continue rising at a faster rate. Sea water has also become more acidic, with surface ocean water 26 per cent more acidic than it was in pre-industrial times.

These changes are expected to continue this century, with the average temperature projected to increase, the average sea level continuing to rise and the ocean becoming warmer and more acidic.

While these increases may sound minor, small changes in average temperature can lead to big changes in the climate system. For example, the IPCC expects extreme weather events such as heatwaves, bushfires, floods and droughts to become more frequent and more intense.

It is not currently possible to state that an individual extreme weather event (such as a drought) is definitely attributable to climate change. However, it is now possible to determine how much more likely it is that a particular extreme temperature event is due to climate change. For example, the autumn heatwaves in Australia in 2014 were found to be 23 times more likely to occur with climate change, compared to conditions without human contribution to climate change.

What is causing climate change?

The climate is affected by the rise in greenhouse gas emissions. Greenhouse gases (GHGs) ‘trap’ heat in the lower parts of the atmosphere around Earth (by absorbing infrared energy coming off the Earth’s surface which could otherwise escape). GHGs include both natural compounds (such as carbon dioxide (CO₂) and methane) and synthetic compounds (such as chlorofluorocarbon (CFC)).

Some fluctuations in the levels of natural GHGs are normal. However, the increasing trend in GHG concentration and the rate of change is beyond the normal variation seen over millennia. Atmospheric GHG concentrations have increased dramatically since industrial times began in the mid-19^th century, driven by the burning of fossil fuels and land clearing. For example, CO₂concentrations recently hit 400 ppm (see Figure 1) after not going above approximately 280 ppm in the last 400,000 years.

Figure 1: Atmospheric levels of CO₂ over time.

Atmospheric levels of CO2 over time.

Source: National Oceanic and Atmospheric Administration (NOAA), NOAA Climate.gov

The IPCC considers that:

Human influence on the climate system is clear, and recent anthropogenic emissions of greenhouse gases are the highest in history ... It is extremely likely that more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic increase in GHG concentrations.

The higher sea levels are a consequence of increased temperature. This is caused by two processes: melting ice sheets (for example, Antarctica and Greenland) and glaciers, as well as the warmer water increasing in volume due to thermal expansion. The rise in ocean acidity is also caused by higher atmospheric levels of CO₂. As these levels increase, ocean absorption of CO₂ becomes greater. The CO₂ then undergoes a chemical reaction with the water to form carbonic acid, thus increasing the level of acidity in the marine waters.

Climate change in Australia

Australia has become 0.9 °C warmer since 1910. The increase in sea surface temperature varies by location. Since 1950, it has risen approximately 0.12 °C per decade in north-west and south-west Australia, while the average temperature rise in south-eastern Australia has been approximately 0.2 °C per decade. The 30 year period from 1985–2014 experienced the warmest average temperature in the last millennium compared to other 30 year periods. Australia’s average temperature is virtually certain to continue rising this century, with inland areas forecast to increase more than coastal areas.

Australian rainfall is also changing, decreasing in winter in south-western Australia and in autumn in south-eastern Australia. In contrast, average annual rainfall has increased in north-western Australia. Weather extremes are also changing, with fewer cold extremes while hot extremes rise in number and temperature. Heatwaves are occurring more often and droughts will become more common in southern Australia. As much of southern Australia becomes hotter and drier, the risk of bushfires is also projected to increase.

Implications for Australia

The IPCC outlined a range of specific risks for Australia from climate change that could affect the country this century. These include:

greater flood damage
limited water resources in southern Australia
greater impacts from heat waves on infrastructure and human health and mortality and
worse harm from bushfires in southern Australia including possible greater human mortality, damaged ecosystems and economic losses.

These risks, and the changes in climate described, have significant implications for Australia across a range of policy areas. It is also worth noting that these threats are not simply theoretical but are already occurring.

In 2012, the Productivity Commission found that all governments should ‘embed consideration of climate change’ in risk management strategies and ensure that regulatory and policy settings allow the risks of climate change to be managed. Some examples of the policy implications of climate change for Australia are set out below.

Health

Climate change is likely to affect human health in a number of ways. For example, there is likely to be an increase in heat-related illnesses such as heatstroke and an increased risk of some infectious diseases (such as those spread by mosquitoes due to mosquitoes’ changing distribution). In turn, this has implications for our health system and policy. The Climate and Health Alliance recently called for a national strategy on ‘Climate, Health and Wellbeing’.

Agriculture

Climate change also presents challenges for agriculture, which is likely to be affected by changes to water availability, changes in growing seasons and the effects of projected increases in extreme weather events. In turn, this may disrupt crop yields, reduce stock numbers, and erode the productivity of farms, threatening their long-term sustainability and viability. While moderate warming may benefit some crops (as long as they are not water stressed) and some colder locations, production levels are projected to decline over much of southern Australia as a result of climate change.

Infrastructure

Infrastructure, including residential and commercial buildings, roads, railways and industry, is also at increasing risk of damage from climate change. Coastal infrastructure is particularly vulnerable, mainly due to an increased risk of flooding from rising sea levels, storm surges, and a higher chance of erosion. This has wide-reaching implications, particularly given that most of Australia’s capital cities are near the coast, along with more than 85% of our population. Many critical services, including hospitals and wastewater treatment, are on the coast and likely to be affected. Indeed, the impact of climate change on coastal communities was the subject of a 2009 parliamentary inquiry. Coastal councils around Australia recently called for the Australian Government to implement the inquiry’s recommendations.

Environment policy and biodiversity

Climate change is increasing the extinction risk faced by non-human species and ecosystems. Many species, especially plants and small mammals, are unlikely to be able to move their geographical range fast enough to keep up with the current and forecast changes to climate. Climate change is also affecting habitat (for example, habitat loss caused by erosion and rising sea levels), food sources, reproduction and migration—all of which can adversely affect the survival of individuals and reproductive success.

These risks are demonstrated by the recent extinction of the Bramble Cay melomys (Melomys rubicola), a type of native rat which lived on Bramble Cay in the Torres Strait, Australia. It is believed to be the first mammal species globally driven to extinction by anthropogenic climate change.

Marine environment, fisheries and tourism

Climate change also affects the marine environment, including fisheries (which in turn can affect food security). Along with increased water temperatures, marine species need to cope with increasing acidification and lower levels of oxygen in the water. Climate change is already causing bleaching and loss of diversity in coral reefs, as evidenced by the recent severe bleaching event in the Great Barrier Reef (see the article on the Great Barrier Reef). These events are likely to become more common in the future. This threatens not only the species that depend on those ecosystems, but may also impact on Australia’s tourism industry.

Other implications

The projected increase in extreme weather events also has implications for the insurance industry, as well as emergency management including natural disaster relief and recovery arrangements.

Commentators have also pointed to the risk that climate change will cause large movements of people—especially from inundated coastal areas or regions affected by extreme weather events and food and water insecurity. This may in turn either trigger or exacerbate international conflict. Both issues have implications for Australia’s immigration, foreign affairs and defence policies. For example, in light of the impact of climate change on islands in the Pacific region, there have been calls for Australia to expand labour mobility opportunities for Pacific Islanders.

Climate adaption policies

While all these risks can be minimised by reducing GHG emissions (climate ‘mitigation’), some level of change is now inevitable. This means we also need to prepare for the effects of climate change, which is referred to as climate ‘adaptation’.

In 2007, the Council of Australian Governments endorsed a National Climate Change Adaptation Framework. In 2015, the Australian Government released a National Climate Resilience and Adaptation Strategy. The Strategy looks at a range of initiatives across key sectors (such as agriculture and health) and identifies principles to guide effective adaptation.

The Government also established the National Climate Change Adaptation Research Facility (NCCARF) in 2008, with $47 million funding. This funding initially ended in June 2013, but in 2014 the Coalition Government provided funding of $9 million to allow NCCARF to continue until 2017.

CSIRO and the Bureau of Meteorology are working together on climate change science as well as adaptation to help Australia better prepare for climate change. However, concerns have been expressed about the capacity of CSIRO to continue its climate science work as a result of a recent controversial restructure.