The IPCC updates its assessment of the global climate system every 6 years, based on global monitoring, new research, improved modelling and expert knowledge. CSIRO and the Bureau of Meteorology complement the IPCC assessment reports with a more focused study of Australia’s climate in their climate projections products. The following section summarises the information from the Australasia chapter of AR5 (Reisinger et al. 2014), the Australian climate projections (Whetton et al. 2015), and the National Climate Resilience and Adaptation Strategy (Australian Government 2015b).

During the past century, Australia’s climate has warmed by 1 °C, and warming is projected to continue through the 21st century (‘virtually certain’), along with other changes in climate (Reisinger et al. 2014). The Paris Agreement from the 2015 Conference of the Parties (COP21) includes a commitment to limit warming globally to less than 2 °C, but achieving this will be a significant challenge. Carbon dioxide has a long lifetime in the atmosphere and can influence the climate system for thousands of years after it is emitted (see Resilience of Australia’s climate) (Solomon et al. 2009).

A warming climate will lead to more frequent heatwaves, which can be responsible for deaths in vulnerable populations such as the sick and elderly. In Victoria, 374 more deaths were recorded during the heatwave of January 2009 than would normally be expected at that time of year (DHS 2009). Heat stress and dehydration also affect the wellbeing of the general population. Conditions for the spread of many diseases will become more favourable, such as the increased geographical spread of pathogen-carrying mosquitoes.

A warming and drying climate is projected to lead to an increase in extreme fire-danger days in southern and eastern Australia. Intense bushfires can destroy housing and infrastructure in affected areas, and may threaten human life.

Australia is likely to experience more frequent intense rainfall events, causing flood damage to our housing and infrastructure (‘medium to high confidence’; Reisinger et al. 2014). It is estimated that the floods of 2010–11 in Queensland cost more than $5 billion in damage and killed 33 people (Holmes 2012). The occurrence of cyclone events varies greatly from year to year and decade to decade. In the long term, there may be a decrease in the overall number of cyclones, but an increase in the proportion of more intense storm events in tropical regions, which may also occur further south of 25° latitude.

Some regions have shown reduced rainfall and increased drought in recent decades. In the Perth region, flows into dams decreased from 338 gigalitres per year in 1911–74 to just 65.8 gigalitres per year in 2006–13 (Water Corporation WA 2009).

Droughts are projected to increase in length and geographical area, leading to increased water shortages in southern Australia. This will largely be driven by a projected reduction in rainfall in winter and spring. Droughts affect agricultural zones, particularly in the Murray–Darling Basin, and far south-eastern and south-western Australia, limiting our ability to grow food and provide pasture for farm animals. Droughts also reduce the water in rivers and streams, required as drinking water for an increasing population and to sustain a range of ecological systems. Our forested regions face an increase in tree mortality and reduced productivity.

Because the surrounding oceans have such a large impact on the variability of the Australian climate, the likely future changes in these systems are an important area of research. Warming of the Indian Ocean because of global warming (Lee et al. 2015) may have played a role in the moderation of the El Niño drying in some parts of Australia in 2015. Furthermore, the nature of ENSO events themselves may change as the climate system warms (e.g. Power et al. 2013, Cai et al. 2015, Chung & Power 2016), with possible consequences for Australia.

Increased temperatures and acidification of the oceans are causing inherent risks to our ecosystems. For example, the impact of bleaching on coral systems is evident in the Great Barrier Reef. The seas surrounding Australia rose by 20 centimetres between 1901 and 2010. Because most Australians inhabit coastal areas, these regions have a high economic and social value. Low-lying regions such as Port Phillip Bay (Melbourne) are particularly vulnerable to sea level rise and storm surge events in the next century. Coastal land, our beaches and amenities will be lost.

The severity of the impacts of weather and climate events depends strongly on the level of vulnerability and exposure to these events. Vulnerability and exposure are dynamic, varying across temporal and spatial scales, and depend on economic, social, geographic, demographic, cultural, institutional, governance and environmental factors. High vulnerability and exposure are generally the outcome of skewed development processes, such as those associated with environmental mismanagement, demographic changes, rapid and unplanned urbanisation in hazardous areas, failed governance, and a scarcity of livelihood options for the poor (Cardona et al. 2012).