Policy paper

Climate science annex

Updated 5 April 2022

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Why we must act

Science is clear that the world is warming, that this is occurring because of human activity, and that left unchecked, continued warming would be deeply harmful, not just to the natural world, but also to human security and wellbeing. Global average temperatures have already risen by around 1.1°C[footnote 1] and 2020 concluded the earth’s warmest 10-year period on record.[footnote 2] Without action to reduce the level of greenhouse gas (GHG) emissions emitted globally down to net zero, climate change is set to continue with increasing temperatures across the world.[footnote 3]

We are already seeing the impacts of climate change across all parts of the world, with many types of extreme weather becoming more frequent and more intense – causing droughts, wildfires and flooding.[footnote 4] The North American heatwave in June 2021, which broke temperature records by over 4°C and reached 49.6°C in Canada, would have been virtually impossible without climate change.[footnote 5] The melting of glaciers and ice sheets is accelerating, with sea levels currently rising at 3.7mm annually.[footnote 6] In the UK we can see a trend towards warmer and wetter winters, along with hotter summers.[footnote 7]

These changes are damaging the land and oceans that support human society and the natural environment. As a result, many species are being driven closer to extinction,[footnote 8] food supplies are being disrupted,[footnote 9] and the health and livelihood of people across the world are being affected.[footnote 10] Climate change disproportionally affects poor and disadvantaged people, with rural, coastal, and indigenous communities facing greater risks from impacts such as rising sea levels, drought, and food shortages.[footnote 11]

There is still uncertainty over the responsiveness of global temperatures to GHG emissions; the Intergovernmental Panel on Climate Change (IPCC) estimate that a doubling of pre-industrial CO2 levels would result in warming in a range of 2.5°C – 4°C.[footnote 12] The higher that temperatures rise, the greater the risk of seeing dangerous low-likelihood, high-impact outcomes. These could include abrupt responses and tipping points such as dieback of the Amazon Rainforest, melting of the polar ice sheets, and the collapse of key ocean currents controlling global weather, which cannot be ruled out.[footnote 13], [footnote 14] To avoid these risks, strong and decisive action is needed to reduce GHG emissions. Limiting further warming decreases the likelihood of more severe and potentially irreversible impacts on people and ecosystems. Action would also provide other co-benefits, such as limiting the rate of ocean acidification and improving air quality. Every additional fraction of a degree of global warming counts – with every 0.5°C of warming there are clearly discernible increases in the intensity of and frequency of impacts.[footnote 15] This is why we should aim to reduce global emissions to net zero as quickly as is practically possible.[footnote 16]

Global temperature goals and emissions pathways

Rapid and deep cuts to emissions are essential to avoid the most dangerous impacts of climate change.[footnote 17] Greenhouse gas concentrations and global temperatures will continue to rise until we reduce GHG emissions to net zero.[footnote 18] In 2015 the Paris Agreement was signed, where 196 parties committed to hold “the increase in the global average temperature to well below 2 degrees above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5°C above pre-industrial levels, recognising that this would significantly reduce the risks and impacts of climate change”. The Agreement recognised that, to achieve this goal, global emissions of greenhouse gases would need to peak as soon as possible, reduce rapidly thereafter, and reach a net zero level in the second half of this century.

As part of the Paris Agreement, countries also committed to reduce or limit their greenhouse gas emissions. These commitments are contained in their Nationally Determined Contributions (NDCs). A number of studies have assessed how close these commitments bring us to staying below 2 degrees.

It is worth noting that these assessments use different assumptions regarding both the extent to which countries will meet their NDCs and, crucially, the actions that will be taken by countries to reduce their emissions after 2030. The latter will be a key determinant of whether the world will meet the long-term global temperature goal.

The Climate Action Tracker (CAT)[footnote 19] estimates that if there were a continuation of the currently implemented global policies these set us on course for a global average temperature rise of 2.1°C to 3.9°C by the end of the century. But if currently pledged ambitions (i.e. those not yet implemented into tangible policies) are implemented this range decreases to 1.9°C to 3.0°C, with a mid-range estimate of 2.4°C. These estimates are also consistent with projections in the UN Environment Programme’s 2020 Emissions Gap Report.[footnote 20] Whilst these assessments show that current NDCs can have a significant impact on projected temperature rises, greater action is still needed if we are to limit global temperature increases to well below 2 degrees.

Adaptation in the UK

Responding to the complexity of climate change demands a multifaceted approach. Regardless of global success in reducing GHG emissions, some future temperature rises are already locked in by historical emissions up to the present day. Even the most optimistic, ambitious emission reduction scenarios suggest approximately 0.5°C of further warming by mid-century compared to the present day.[footnote 21] Furthermore, future global emissions pathways are highly uncertain, so it is essential that the UK’s adaptive capacity is rapidly developed to prepare for, and bolster our resilience to, the inevitable near-term and potential future impacts of climate change.

To prepare for these eventualities, the UK is already considering climate risks and what actions will be required through its 5-yearly policy cycle of a Climate Change Risk Assessment followed by a National Adaptation Programme (NAP). The government’s Third Climate Change Risk Assessment will be published in January 2022 and will outline government views on the key risks and opportunities the UK will face from climate change. The Climate Change Committee’s 2021 Independent Assessment of UK Climate Risk identified 8 risk areas that will require the most urgent attention in the next 2 years.[footnote 22] These are applicable even if global warming is limited to 1.5°C.

  • Risks to the viability and diversity of terrestrial and freshwater habitats and species from multiple hazards
  • Risks to soil health from increased flooding and drought
  • Risks to natural carbon stores and sequestration from multiple hazards leading to increased emissions
  • Risks to crops, livestock and commercial trees from multiple hazards
  • Risks to supply of food, good and vital services due to climate-related collapse of supply chains and distribution networks
  • Risks to people and the economy from climate-related failure of the power system
  • Risks to human health, wellbeing and productivity from increased exposure to heat in homes and other buildings
  • Multiple risks to the UK from climate change impacts overseas

The NAP is a cross-department collaboration, bringing together government’s policies on managing climate risks in one place. The second NAP sets out how we will address climate risks for the period 2018 to 2023, including risks to terrestrial, coastal, marine, and freshwater ecosystems, soils and biodiversity; and flooding and coastal change risks to communities, businesses and infrastructure.

Future developments in climate science

In recent years the debate and focus of scientific research has shifted from whether climate change is happening and/or is being caused by human activity, to the range of the expected impacts and the level of action required to address climate change through a combination of adaptation and mitigation. We need to better understand the nature, magnitude and rate of climate change. Preparing for unavoidable changes to the climate will require more local analysis and more information on how global warming relates to local-scale changes in weather and climate extremes. Further research is also needed around stronger mitigation actions to inform climate policy that can get us to net zero.

Our knowledge has increased significantly but many key research priorities remain, including deepening our understanding around the 4 questions government posed to the Met Office this year.[footnote 23]

  • What current weather and climate risks and impacts are expected globally and in the UK?
  • What are the future risks and impacts from weather and climate that we need to avoid or need to adapt to?
  • What are the carbon budget and mitigation scenarios that will avoid the most dangerous impacts of global climate change?
  • What impacts and opportunities from mitigation and adaptation actions are needed to proceed towards a resilient and net zero future?

The UK has also recently committed £1.2 billion of funding to develop a new state-of-the-art supercomputer for the Met Office. This will help ensure government, industry and communities are better prepared for the impacts from a changing climate through increased amounts of data. Examples include the provision of very detailed localised climate information to improve city planning and public transport infrastructure.

Climate science continues to rapidly improve and develop. This year saw the publication of the Working Group I (WGI) contribution to the IPCC’s Sixth Assessment Report (AR6). The report addresses the most up-to-date physical understanding of the climate system and climate change, bringing together the latest advances in climate science. WGII and WGIII contributions to AR6 will be published in 2022 and respectively cover the impacts of climate change on people and nature, and the options for reducing GHG emissions and removing GHG from the atmosphere.

The main conclusions of WGI are a reinforcement of the consensus on climate science: that there is absolutely no doubt that human activities have warmed the planet and are causing widespread and rapid changes to the climate. Without immediate and drastic action, the impacts will be more severe and frequent. It shows that we are already feeling the effects of climate change and know that some changes to the planet are already irreversible on timescales of centuries to millennia. However, with immediate, concerted action to reduce emissions now, the worst impacts can still be averted. Technologies to remove CO2 directly from the atmosphere or ocean can also help, but to adhere to the temperature goal of the Paris Agreement ambitious action on emission reductions is still required, and is needed today.

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Endnotes

  1. IPCC (2021), ‘Working Group I Contribution to the IPCC 6th Assessment Report, Climate Change 2021: The Physical Science Basis’, Paragraph A.1.2, Summary for Policymakers. ↩

  2. Met Office (2021), ‘2020 ends earth’s warmest 10 years on record’. ↩

  3. IPCC (2021), ‘Working Group I Contribution to the IPCC 6th Assessment Report, Climate Change 2021: The Physical Science Basis’, Paragraph D.1.1, Summary for Policymakers. ↩

  4. IPCC (2021), ‘Working Group I Contribution to the IPCC 6th Assessment Report, Climate Change 2021: The Physical Science Basis’, Paragraph A.3.2 and A.3.5, Summary for Policymakers. ↩

  5. Philip, S. Y. et al (2021), ‘Rapid attribution analysis of the extraordinary heatwave on the Pacific Coast of the US and Canada’. ↩

  6. IPCC (2021), ‘Working Group I Contribution to the IPCC 6th Assessment Report, Climate Change 2021: The Physical Science Basis’, Paragraph A.4.3 and A.1.7, Summary for Policymakers. ↩

  7. Kendon, M. et al (2021), ‘State of the UK Climate 2020’. ↩

  8. IPCC (2019), Special Report on Climate Change and Land, Section 2.2.4, Chapter 2, Food Security, Land-Climate interactions. ↩

  9. IPCC (2019), Special Report on Climate Change and Land, Chapter 5 Executive Summary. ↩

  10. IPCC (2019), ‘Special Report on Climate Change and Land’, Chapter 5 Executive Summary. ↩

  11. IPCC (2018), IPCC Special Report on Global Warming of 1.5°C, Chapter 3 Section 3.5.2.3 and Paragraph B5.1 Summary for Policymakers. ↩

  12. IPCC (2021), ‘Working Group I Contribution to the IPCC 6th Assessment Report, Climate Change 2021: The Physical Science Basis’, Paragraph A.4.4 Summary for Policymakers. ↩

  13. IPCC (2021), ‘Working Group I Contribution to the IPCC 6th Assessment Report, Climate Change 2021: The Physical Science Basis’, Paragraph C.3.2, Summary for Policymakers. ↩

  14. IPCC (2021), ‘Working Group I Contribution to the IPCC 6th Assessment Report, Climate Change 2021: The Physical Science Basis’, Box TS.9, Technical Summary. ↩

  15. IPCC (2021), ‘Working Group I Contribution to the IPCC 6th Assessment Report, Climate Change 2021: The Physical Science Basis’, Paragraph B.2.2, Summary for Policymakers. ↩

  16. IPCC (2021), ‘Working Group I Contribution to the IPCC 6th Assessment Report, Climate Change 2021: The Physical Science Basis’, Paragraph D.1, Summary for Policymakers. ↩

  17. Lowe, J. et al (2019), ‘Links between emissions pathways and time lags in Earth’s climate system’. ↩

  18. PCC (2021), ‘Working Group I Contribution to the IPCC 6th Assessment Report, Climate Change 2021: The Physical Science Basis’, Paragraph B.1 and D.1 Summary for Policymakers. ↩

  19. Climate Action Tracker (2021), ‘Warming Projections Global Update May 2021’. ↩

  20. UNEP (2020), ‘Emissions Gap Report 2020’. ↩

  21. IPCC (2021), ‘Working Group I Contribution to the IPCC 6th Assessment Report, Climate Change 2021: The Physical Science Basis’, Box TS.1 and Table 1, Technical Summary. ↩

  22. CCC (2021), ‘Independent Assessment of UK Climate Risk’, Executive Summary. ↩

  23. Met Office, Hadley Centre Climate Programme ↩

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