POST - Parliamentary Office of Science and Technology

Limiting Global Warming to 1.5°C

Published Monday, February 11, 2019

Under the Paris Agreement, almost all governments worldwide have agreed to collectively limit global warming to 'well below' 2°C above pre-industrial temperatures, and to 'pursue efforts' to limit this warming to 1.5°C. However, there has been 1°C of warming to date, and current international pledges could result in 3°C or more. A 2018 UN Special Report examined how peak global warming could be limited to 1.5°C above pre-industrial temperatures, and the implications of doing so. This POSTnote outlines key messages from the UN Special Report, and UK responses to preventing and adapting to climate change.

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Global surface temperature anomalies, Jan-Jun '16. Credit: NASA Goddard Space Centre

The UN Special Report found that:

  • There has been around 1°C of global warming to date, almost entirely caused by human activities that emit greenhouse gases (GHGs) - particularly carbon dioxide (CO2) and methane.
  • Global warming of 1.5°C would result in risks to natural and human systems, including ecosystems, wildlife, sea level rise, food and water security, and human health and well-being.
  • There are different ways to reduce human-induced GHG emissions to limit warming to 1.5°C. The Report broadly finds that global CO2 emissions would likely need to peak in the near future, roughly halve by around 2030, and reach net zero around 2050.
  • CO2 will likely need to be removed from the atmosphere by greenhouse gas removal (GGR) processes. The slower the rate of emissions reductions in the next few decades, the greater the amount of GGR required later this century. Using GGR at the scales likely required to limit to 1.5°C could present substantial technological, economic and social challenges.

IPCC experts suggest that in any case, the emissions reductions required imply "rapid, far-reaching changes on an unprecedented scale" to all sectors of the economy.

The UK Government has climate policy in place for mitigating against and adapting to climate change. 

  • There is a long-term target of reducing UK GHG emissions by 80% (compared to 1990 levels) by 2050. 
  • The UK Government is expected to legislate for a "net zero" target at some point in the future. In 2018 it requested advice from the independent Committee on Climate Change on the long-term level of emissions that would contribute to a well below 2°C, and 1.5°C, global warming target.

Acknowledgements

POSTnotes are based on literature reviews and interviews with a range of stakeholders, and are externally peer reviewed. POST would like to thank interviewees and peer reviewers for kindly giving up their time during the preparation of this briefing, including:

  • Siobhan Browne, BEIS*
  • Peter Coleman, BEIS*
  • Dr Jolene Cook, BEIS*
  • Dr Steve Forden, BEIS*
  • Dr Cathy Johnson, BEIS*
  • Dr Phil Raymond, BEIS*
  • Dr Rhian Rees-Owen, BEIS*
  • Dr James Pearce-Higgins, British Trust for Ornithology
  • Dr Richard Millar, Committee on Climate Change*
  • Mike Thompson, Committee on Climate Change*
  • David Style, Committee on Climate Change*
  • Mike Childs, Friends of the Earth*
  • Dr Joeri Rogelj, Imperial College*
  • Prof Richard Betts, Met Office
  • Chris Jones, Met Office*
  • Prof Jason Lowe, Met Office*
  • Richard Barker, National Physical Laboratory
  • Steve Pye, UCL*
  • Prof Rachel Warren, UEA*
  • Prof James Ford, University of Leeds*
  • Prof Gideon Henderson, University of Oxford*
  • Members of the POST Board*

* denotes stakeholders who acted as external reviewers of the POSTnote.

Defra were invited to comment on the POSTnote but did not do so.

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The Parliamentary Office of Science and Technology produces independent, balanced and accessible briefings on public policy issues related to science and technology.