Limiting Global Warming to 1.5°C: what it means and how to achieve it


On 8 October the Intergovernmental Panel on Climate Change (IPCC) released a special report, Global Warming of 1.5°C, a summary of the state of global research on the impacts of warming at this level and the emissions reduction pathways needed to achieve it.

The report was called for as part of the compromises underpinning the Paris Agreement; small island nations fought at Paris for recognition of a 1.5°C goal, as they would still expect to be inundated under the more broadly accepted 2°C goal. It will be an influential touchstone in global and Australian policy making. Under Paris, nations are expected to elaborate long-term emissions pathways and to enhance and extend their commitments regularly.

The report’s key findings are:

Warming so far and projections

Global mean surface temperatures have already warmed around 1°C from pre-industrial levels due to human activity, with consequences for sea level, ice cover, temperature extremes, storms and the health of many ecosystems.

Cumulative emissions to date will cause further warming and changes for centuries to come.

Global warming is likely to reach 1.5°C between 2030 and 2052 at the current rate.

Impacts of 1.5°C and 2°C

Compared to 2°C, 1.5°C of warming would lead to:

  • mean temperatures, extreme temperatures in inhabited areas, heavy rainfall events and drought events that are less unfavourable;
  • lower and slower rise in sea levels, allowing more time for adaptation or migration of coastal and island communities;
  • reduced losses of ecosystems and their services to humans. However, losses compared to today would still be significant. For instance, at 1.5°C coral reefs would decline by 70-90% from today (though by >99% at 2°C);
  • lower risks and impacts in relation to health, crop yields, water supply and growth;
  • less need for investments in adaptation to mitigate risks.

Figure 1 – IPCC 'burning embers' chart illustrates state of research on impacts of increasing temperatures and high (H) or medium (M) confidence levels

Figure 1IPCC ‘burning embers’ chart illustrates state of research on impacts of increasing temperatures and high (H) or medium (M) confidence levels

Mitigation pathways

Stabilising temperatures at any level requires reducing net global greenhouse gas emissions to zero (taking account of sequestration of carbon, such as through forest growth or carbon capture and storage). To stabilise at 2°C would require global CO2 emissions reductions of about 20% by 2030 and net zero around 2075. To stabilise at 1.5°C would require emissions reductions of about 45% by 2030 and net zero around 2050.

The IPCC has not included ‘solar radiation management’, a form of ‘geoengineering’, in assessing mitigation pathways. Such technologies to partially block out the sun have been proposed to manage temperature increase, but are poorly understood, present substantial risks, and would be only partial and temporary solutions.

Figure 2 – IPCC chart of modelled emissions pathways capable of limiting temperature increases to 1.5C

Figure 2 IPCC chart of modelled emissions pathways capable of limiting temperature increases to 1.5C


Achieving mitigation

Achieving 1.5°C requires rapid and far-reaching transitions in energy, land, urban, infrastructure and industrial systems. Deep emissions reductions in all sectors, a wide portfolio of mitigation options and a significant increase in investment in those options are required.

All scenarios for 1.5°C require some level of carbon dioxide removal, achieved through afforestation and improvements to land management, or through bioenergy with carbon capture and storage. Scenarios with slower reductions in emissions entail equivalently larger and longer-term dependence on carbon removal. Large scale deployment of carbon removal has multiple feasibility and sustainability challenges, such as competition with land use for food and fibre production.

Implications for national policies

The sum of existing 2030 emissions reduction commitments from all nations under the Paris Agreement is not adequate to achieve 1.5°C, and is more consistent with temperatures hitting 3°C by 2100 and continuing to increase thereafter. Even very rapid reductions in emissions beyond 2030 would not be able to keep temperature increases to 1.5°C if nations do not commit to and achieve deeper 2030 reductions.

Implications for Australia

The IPCC does not single out Australia and is circumspect in its statements about existing national commitments and policies. However, the suggestion is that all countries would need to deepen their emissions targets and increase associated policies and investments even to achieve 2°C, let alone 1.5°C. The technical, economic and political challenges involved are serious. The consequences of failure are even more so. This report will be widely cited in international negotiations and national policy debates to argue for deeper targets.

The Coalition Government is not considering any change to the existing 26-28% 2030 target, nor any additional policies to achieve it. The Federal ALP proposes a 45% 2030 target and (like most Australian States) net zero by 2050 – more consistent with 2°C if developed countries are expected to move faster than developing countries. The Federal Greens propose a 60-80% 2030 target and net zero by 2040, more consistent with 1.5°C.

The feasibility and desirability of deeper targets will be much discussed. While recent climate policy debate in Australia has focused on the electricity sector, since electricity is only around a third of current emissions, other sectors including industry will increasingly be in the spotlight.

Figure 3 - Australian greenhouse emissions by sector, historical and 2017 business-as-usual projections, with alternate 2030 targets

Figure 3Australian greenhouse emissions by sector, historical and 2017 business-as-usual projections, with alternate 2030 targets



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Tennant Reed
Tennant is Principal National Adviser – Public Policy at Ai Group. He has worked heavily on climate and energy issues, advising Ai Group’s Leaders’ Group on Energy and Climate Policy and developing reports on natural gas supply, energy prices and energy efficiency. He also works on a range of issues related to manufacturing and innovation. Previously he was an adviser in the Department of Prime Minister and Cabinet, working on fiscal policy, stimulus and infrastructure.

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