UCL News


Extreme heat poses ‘unacceptably high’ health risk worldwide

29 November 2018

Rising temperatures as a result of climate change are already exposing people to health risks across the globe, according to a new report from 27 global institutions co-led by UCL researchers.

Forest fire

Outdoor workers, people with underlying health conditions and the urban elderly are especially at risk, according to the findings published today in The Lancet.

“Exposure and vulnerability to extreme heat is unacceptably high and rising for people all around the world. Heat stress is hitting hard. In high temperatures, outdoor work, especially in agriculture, is hazardous,” said Professor Hugh Montgomery, (UCL Medicine), Co-Chair of the Lancet Countdown and Director of the UCL Institute for Human Health and Performance.

“Areas from Northern England and California, to Australia are seeing savage fires with direct deaths, displacement and loss of housing as well as respiratory impacts from smoke inhalation.”

Leading doctors, academics and policy professionals from 27 organisations have contributed analysis and jointly authored the report. As members of The Lancet Countdown: Tracking Progress on Health and Climate Change, partners behind the research include the World Bank, World Health Organization (WHO), UCL and Tsinghua University, among others.

The report investigated the impact of climate change on health in 478 cities across the globe, identifying health impacts including:

  • 157 million more vulnerable people were subjected to a heatwave last year than in 2000, and 18 million more than in 2016.
  • 153 billion hours of work were lost in 2017 due to extreme heat as a result of climate change. China alone lost 21 billion hours, the equivalent of a year’s work for 1.4% of their working population. New methodologies have captured this data for the first time.
  • Rising ambient temperatures are placing vulnerable populations at increased risks across all regions of the world. Europe and the East Mediterranean are particularly at risk, markedly more so than in Africa and Southeast Asia, most likely due to ageing populations living in cities, with 42% and 43% of people over 65 vulnerable to heat exposure.
  • The report highlights that heat greatly exacerbates urban air pollution, with 97% of cities in low- and middle- income countries not meeting WHO air quality guidelines. 
  • Heat stress, an early and severe effect of climate change, is commonplace and people, and the health systems we rely on, are ill equipped to cope. 
  • Rising temperatures and unseasonable warmth is responsible for cholera and dengue fever spreading, with vectorial capacity for their transmission increasing across many endemic areas. 
  • The mean global temperature change to which humans are exposed is more than double the global average change, with temperatures rising 0.8°C in inhabited areas versus 0.3°C.

The authors say that urgent steps are needed to protect people now from the impacts of climate change. In particular, stronger labour regulations could protect workers from extremes of heat, and hospitals and health systems need to be better equipped for extreme heat.

But the report authors also stress that there are limits to adapting to the temperature increases, so the need for reducing emissions is critical.

"Whilst the impacts are felt disproportionately by those least responsible for climate change, no country is immune. Our 2018 report makes clear that without urgent action to reduce greenhouse gas emissions, health systems around the world will quickly become overwhelmed by the compounded impacts of a changing environment," said first author Dr Nick Watts (UCL Institute for Global Health), Executive Director of the Lancet Countdown.

2018 has been an even hotter year in many parts of the world and another recent report found that this summer’s heat wave was twice as likely to have happened as a result of man-made climate change.

With 51% of the cities surveyed in the report expecting climate change to seriously compromise their public health infrastructure, the researchers say the need to ensure health systems, hospitals, and clinics can cope when extreme heat strikes is clear. Leaders in 65% of the cities said they have either already completed or are currently doing climate change risk assessments but spending on climate adaptation for health is estimated to be just 4.8% (£11.68 billion) of all adaptation spending which is woefully inadequate, the report warns. 

“The world has yet to effectively cut its emissions. The speed of climate change threatens our, and our children’s lives. Following current trends we exhaust our carbon budget required to keep warming below two degrees, by 2032. The health impacts of climate change above this level above this level threaten to overwhelm our emergency and health services," said Professor Anthony Costello (UCL Institute for Global Health), Co-Chair of Lancet Countdown and former Director at WHO.

Co-authors of the report included 14 UCL researchers in the Faculties of Medical Sciences, Population Health Sciences, Mathematical & Physical Sciences, Life Sciences, Social & Historical Sciences, and the UCL Bartlett Faculty of the Built Environment.

Lancet Countdown infographic



  • Forest fire in Indonesia (Credit: Donal Bason / USAID Biodiversity & Forestry, Source: Flickr)
  • Infographic credit: Lancet Countdown


Media contact

Chris Lane

Tel: +44 (0)20 7679 9222

Email: chris.lane [at] ucl.ac.uk