Revealing the impact of more extreme heat in US cities

Projections show our climate will warm above agreed levels. How dangerous might this extra heat be to public health?

The challenge

Based on the current documented commitments of nations states, our world is heading towards a 3°C rise in mean temperature. That’s despite the 2015 Paris Agreement requiring countries to limit warming to 2°C – with an ambition of 1.5°C or less.

What are the real-world effects of this additional degree of warming? One of them is more heat-related deaths. Nearly all land regions are expected to endure increases in temperature extremes greater than the rise in mean temperatures. Yet this remains an understudied impact of the climate crisis.

Studies analysing the variation between 2°C and 1.5°C scenarios tell us that half a degree lower significantly reduces dangerous heat stress and temperature spikes around the world. To grasp the full implications of 3°C of warming, we need more explicit data on how the increase might affect heat and human mortality.

What we're doing

Using daily counts of deaths and mean temperatures for 15 US cities, we integrated our statistical modelling with existing and newly created climate models projecting 1.5, 2 and 3°C of warming.

We found that by limiting temperature rises to 2°C, each city would see between 129 and 319 fewer hot days per decade. Meeting the 1.5°C Paris goal would make the reduction between 202 and 510 days per decade, per city.

In these 15 cities alone, restricting warming could save thousands of lives from extreme heat. We predicted mortality from 1-in-30-year events – a highly relevant frequency for governments determining their climate change mitigation policies. The figures for just one city, New York, are stark: heat-related deaths from such an event in a 2°C world could be cut by 1,980 compared to the same event in a 3°C world. A 1.5°C world might save 2,720 lives.

How it helps

Meeting the agreed Paris goals could significantly reduce exposure to extreme heat and its related mortality in these cities.

We aimed to present this fresh insight into the impact of extreme heat at an opportune moment – as governments should have been submitting their updated commitments to the UN. To date, 189 countries have ratified the Paris Agreement, but most are yet to file their new and supposedly improved contributions to mitigating climate change.

Our findings show clear health benefits of greater mitigation and offer another reminder of the importance of meeting the Paris targets.


  • Dr Eunice Lo (PI)
  • Dr Dann Mitchell
  • Dr William Roberts
  • Peter Uhe
  • Dr Gethin Williams

Eunice Lo Lead researcher profile

Dr Eunice Lo, Research Associate in climate change, extreme weather and human health

Partner organisations

  • London School of Hygiene & Tropical Medicine
  • University of Washington
  • Union of Concerned Scientists
  • University of Oxford
  • Committee on Climate Change


  • Cabot Institute for the Environment
  • Union of Concerned Scientists
  • Natural Environmental Research Council
  • Medical Research Council
Edit this page