Overview of change

Climate change is expected to worsen the frequency, intensity and impacts of some types of extreme weather events,1,2,3 such as sea level rise increasing the impact of coastal storms. Coastal areas in the UK and Northern Europe are likely to experience an increase in ‘compound flooding’, where storm surges and heavy rainfall combine, in the coming decades, particularly in ‘hotspots’ such as Devon, Cornwall and the Bristol Channel.4 Extreme weather events are usually defined as being rare at a particular place and time of year, such that the event is above (or below) a threshold value near the upper (or lower) ends of the range of its observed values in a specific region. A weather or climate event, even if not extreme in a statistical sense, can also still lead to extreme conditions or impacts, either by crossing a critical threshold in a social, ecological or physical system, or by occurring simultaneously with other events, such as where and when a hurricane makes landfall. Some climate extremes (such as droughts) may be the result of an accumulation of weather or climate events that are, individually, not extreme themselves (though their accumulation is extreme).5 In the UK such events include floods, heatwaves and droughts.6,7 There has been a rise in global climate-related disasters, including extreme weather events, from 3,656 (1980–1999) to 6,681 climate-related disasters in the period 2000–2019 with 510,837 deaths and 3.9 billion people affected. For example, the number of major floods have more than doubled between these time periods, from 1,389 to 3,254, while the incidence of storms grew from 1,457 to 2,034.8 Research suggests that climate change in the 21st Century has already substantially increased the probability of unprecedented hot and wet weather events.9,10,3

Challenges and opportunities

Under a high greenhouse gas emissions scenario, research suggests heatwaves will kill an additional 73 people per 100,000 by 2100. But under lower emission scenarios these additional deaths would decrease to 11 per 100,000.11 Depending on the extent of emissions, within 50 years, 2–3.5 billion people, mostly the poor who can’t afford air conditioning, may be living in a climate that historically has been too hot for human activities, such as agriculture. Under a business-as-usual scenario for emissions, mean annual temperatures in hotter regions such as the Middle East and North Africa are projected to rise from 20°C to 29.0°C by 2070, conditions that presently occur only in 0.8% of the global land surface.12 In this region, 80% of the most populated cities are expected to be in heatwave conditions for 50% of the warm season.13 In nearly every part of the world heatwaves have been increasing in frequency and duration since the 1950s. From 1950–2017, the Mediterranean saw an increase in heatwaves by 2 days a decade, but the trend from 1980 to 2017 had seen that accelerate to 6.4 days a decade.14 In the UK, climate change is projected to raise average summer temperatures by 5°C by 2070, and up to 5,000 people could die each year as a result of heat in the UK by 2050 without more effective adaptation.15,16

In 2018, globally, around 108 million people required help from the international humanitarian system as a result of storms, floods, droughts and wildfires. By 2030, it is estimated that this number could increase by almost 50% at a cost of around US$20 billion a year. These growing risks highlight the need to improve the implementation and effectiveness of early warning systems worldwide to strengthen countries’ resilience to multiple weather-, climate- and water-related hazards.17 For example, the heatwave in Siberia in 2020 triggered widespread fires, with 1.15 million hectares burning in late June, associated with a release of about 56 million tonnes of carbon dioxide, more than the annual emissions of some industrialised countries such as Switzerland and Norway.18

If climate change risks, driven by extreme weather conditions, to global supply chains are not managed, impacts may occur for food production, natural resources and transportation worldwide. These impacts on the food, mining and logistics sectors could cascade into other interlinked global supply chains.19

Key unknowns

Many of the potential serious risks of climate change have been omitted from economic assessments because of the difficulties in quantifying precise impacts, such as stronger tropical cyclones, extreme heat impacts, more frequent and intense flood risks and droughts, as well as risks not yet anticipated.20

There is the potential for risks to interact with each other, such as failure of climate change mitigation and adaptation, and extreme weather events. Extreme heatwaves could accelerate climate change by releasing large amounts of stored carbon from affected ecosystems, and at the same time intensify water crises and/or food scarcity.21,22,23

Earth’s tropics are expanding polewards into regions like the Mediterranean, southern Australia and southern California, and that expansion is driven by the effects of human-caused climate change on the oceans. This process could shift storm paths and cause more severe wildfires and droughts in places like California and Australia that are already water stressed.24

Key questions for Parliament

  • What science and early warning systems should be invested in for prevention, climate change adaptation and disaster risk reduction?4
  • Whether UK progress on adaptation measures for extreme weather events is sufficient,25,26 when the third Climate Change Risk Assessment is published in the summer of 2021.27
  • The implications of COP26 outcomes for climate change risks arising from extreme weather events.28

Likelihood and impact

There is a growing risk of more developed countries being affected by climate impacts from extreme weather, but less developed countries in the global south will be disproportionally affected.29

Research for Parliament 2021

Experts have helped us identify 30 areas of change to help the UK Parliament prepare for the future.


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  2. Christidis, N, et al. (2021). Record‐breaking daily rainfall in the United Kingdom and the role of anthropogenic forcings. Atmospheric Science Letters, e1033
  3. World Meteorological Organisation. (2020). State of the Global Climate 2020, Provisional Report.
  4. Bevacqua, E, et al. (2019). Higher probability of compound flooding from precipitation and storm surge in Europe under anthropogenic climate change. Science Advances, vol 5 (9), eaaw5531
  5. IPCC. (2012). Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation. A Special Report of Working Groups I and II of the Intergovernmental Panel on Climate Change
  6. Sambrook, K, and Richardson, T. (2019). Climate change means more extreme weather – here’s what the UK can expect if emissions keep increasing. The Conversation.
  7. Kendon, M, et al. (2020). State of the UK Climate 2019. International Journal of Climatology, vol 40, Issue S1 Supplement: State of the UK Climate 2019
  8. UNDRR and CRED. (2020). Human costs of disasters. An overview of the last 20 years, 2000-2019
  9. Diffenbaugh, N. (2020). Verification of extreme event attribution: Using out-of-sample observations to assess changes in probabilities of unprecedented events. Science Advances, vol 6 (12), eaay2368
  10. Vautard, R, et al. (2020). Human contribution to the record-breaking June and July 2019 heatwaves in Western Europe. Environ. Res. Lett., vol 15, 094077
  11. National Bureau of Economic Research. (2020). Valuing the Global Mortality Consequences of Climate Change Accounting for Adaptation Costs and Benefits. Working Paper 27599
  12. Xu, C, et al. (2020). Future of the human climate niche. PNAS, vol 117 (21) 11350-11355
  13. Varela, R, et al. (2020). Persistent heat waves projected for Middle East and North Africa by the end of the 21st century. PLoS ONE, vol 15(11): e0242477
  14. Perkins-Kirkpatrick, S, and Lewis, S. (2020). Increasing trends in regional heatwaves. Nature Communications, vol 11, Article number: 3357
  15. Brimicombe, C. (2020). Heatwaves are an invisible killer – and the UK is woefully unprepared. The Conversation.
  16. Brimicombe, C. (2020). Heatwaves: An invisible risk in UK policy and research. Environmental Science & Policy, vol 116, Pgs 1-7
  17. World Meteorological Organisation. (2020). 2020 State of Climate Services, Risk Information and Early Warming Systems. WMO-No. 1252
  18. Ciavarella, A, et al. (2020). Prolonged Siberian heat of 2020. World Weather Attribution Report.
  19. Ghadge, A, et al. (2020). Managing climate change risks in global supply chains: a review and research agenda. International Journal of Production Research, vol 58(1), pgs 44-64
  20. DeFries, R, et al. (2019). The missing economic risks in assessments of climate change impacts. LSE Grantham Research Institute on Climate Change and the Environment.
  21. Future Earth, (2020). Risks Perceptions Report 2020: First Edition. Future Earth
  22. Raymond, C, et al. (2020). Understanding and managing connected extreme events. Nature Climate Change, vol 10, pgs 611–621
  23. Lawrence, J, et al. (2020). Cascading climate change impacts and implications. Climate Risk Management, vol 29, 100234
  24. Yang, H, et al. (2020). Tropical Expansion Driven by Poleward Advancing Midlatitude Meridional Temperature Gradients. JGR Atmospheres, vol 125 (16), e2020JD033158
  25. Murphy, J, et al. (2020). UKCP Additional Land Products: Probabilistic Projections of Climate Extremes. Met Office
  26. Kennedy-Asser, T, et al. (2021). Evaluating heat extremes in the UK Climate Projections (UKCP18). Environ. Res. Lett., vol 16, 014039
  27. Climate Change Committee, (2021). UK Climate Change Risk Assessment Evidence Report
  28. UK COP 26 Presidency. (2020). Climate Change and Health.
  29. Eckstein, D, et al. (2020). Global Climate Risk Index 2020. Who Suffers Most from Extreme Weather Events? Weather-Related Loss Events in 2018 and 1999 to 2018

Image: ESA/NASA–A. Gerst under CC BY-SA 3.0 IGO

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