Effective emissions reductions efforts and climate change adaptation together will bring important benefits: social, environmental and economic impacts will be lower; new opportunities can be fully exploited; and fresh thinking about climate risks will stimulate innovation in other fields. (Australian Government 2015b)

The outlook for Australia’s climate is influenced by the global climate outlook. Without mitigation to reduce GHG emissions, modelling suggests that growth in population and economic activities alone will see the median surface temperature increase by 3.7–4.8 °C above 1850–1900 temperatures (Edenhofer et al. 2014b). However, under the Paris Agreement, 195 nations have agreed to hold the increase in the global average temperature to below 2 °C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5 °C.

For it to be likely that warming during the 21st century will remain below 2 °C, CO₂-e concentrations need to be stabilised at less than about 450 parts per million (ppm) by 2100. This would require a reduction in global anthropogenic GHG emissions of 40–70 per cent by 2050 compared with 2010, and near zero emissions or below in 2100. Concentrations of about 500 ppm CO₂-e by 2100 are still likely to limit temperature change to less than 2 °C and are likely to result in temperature rise of less than 3–4 °C by 2100. This scenario would require global 2050 emissions levels to drop by about 25–55 per cent from the level in 2010 (Edenhofer et al. 2014b).

Thus, the outlook for Australia’s climate depends on the effectiveness of international and national efforts to reduce GHG emissions. Mitigation and adaptation require international and domestic cooperation. International cooperation provides the overarching frameworks and drivers for mandating domestic policy and action. Internationally, the United Nations Framework Convention on Climate Change provides this, and the Paris Agreement provides the latest mechanism for the implementation of the framework. Domestically, there needs to be bipartisan agreement to act on climate change and implement policies that will reduce or mitigate emissions.

Serious mitigation strategies are required. Encouragingly, robust evidence shows that reductions in the carbon intensity of electricity generation, efficiency enhancements and behavioural changes will lead to a reduction in energy demand that does not compromise development (Edenhofer et al. 2014b).

In scenario modelling using the low-concentration pathway (e.g. 450 ppm by 2100), CO₂ emissions from the energy supply sector show a reduction greater than 90 per cent below 2010 levels by 2040 and 2070. Low-carbon electricity supply from renewable energy, nuclear energy, and CO₂ capture and storage increases to more than 80 per cent by 2050, when fossil fuel power generation is completely phased out (Edenhofer et al. 2014a). Reducing energy demand in the near future has the added benefits of helping industry avoid locking into carbon-intensive infrastructure, such as new coal-fired power plants, and reducing the risk of energy supply fluctuations.

Changes in human behaviour and lifestyle can significantly reduce emissions through changes in consumption patterns, adoption of energy savings measures, dietary change and reduction in food wastes (Edenhofer et al. 2014a). Land-use mitigation—including changes to forest management (including afforestation, sustainable management and reducing deforestation), changes in cropland management, changes in grazing land management and restoration of organic soils—are also considered to be potentially effective (Edenhofer et al. 2014a). In principle, mechanisms that set a carbon price, including cap-and-trade systems and carbon taxes, can achieve cost-effective mitigation. However, success of these mechanisms is varied, and dependent on national circumstances and policy design (Edenhofer et al. 2014a).

In Australia, mitigation activities include a broad suite of programs ranging from reducing emissions, enhancing energy efficiency, increasing renewable energy use, improving industrial processes, increasing sustainable transport use and enhancing carbon sinks (Australian Government 2015b), including sequestering carbon in the soil and undertaking large-scale landscape revegetation programs. Renewable energy targets and the development of more resilient systems of agricultural production are also part of the Australian strategy.

The extent to which temperatures will rise depends on the effectiveness of international actions to reduce emissions, as discussed above. The risk of catastrophic or abrupt climate change increases as the magnitude of the temperature rise increases (Stocker et al. 2013a). For example, global mean sea level rise will continue beyond 2100 because of thermal expansion (0.4 metres for 2081–2100 under the low-concentration pathway), whereas mass loss by ice sheets, which may be irreversible, would cause larger sea level rise (7 metres for a temperature rise greater than 4 °C) (Stocker et al. 2013a).

Mitigation efforts to reduce GHG emissions will aim to minimise the extent of future climate change and prevent catastrophic climate change tipping points. Mitigation will not return the climate system to its pre-industrial state—it is important to note that, despite international and domestic mitigation efforts, temperatures will remain high for many centuries even after a complete cessation of net anthropogenic CO₂ emissions. Adaptation will therefore be an important component in the way society handles climate change.