Holding global temperature rise to 1.5C above pre-industrial levels, rather than 2C or 3C, could help prevent thousands of deaths in US cities during heatwaves, a new study says.
The research projects heat-related deaths for 15 cities across the US under the different levels of future warming. The results suggest that major cities, such as New York City and Los Angeles, could see hundreds or thousands more deaths in extreme heat without greater ambition in global emissions cuts.
The findings provide “compelling evidence for the heat-related health benefits of limiting global warming to 1.5C” in the US, the study concludes.
The work “breaks new ground”, a scientist not involved in the work tells Carbon Brief, and shows that “the strongest climate policies, both for mitigation and adaptation, will save lives and help us to avoid never-before-seen human suffering from extreme heat”.
As global temperatures increase, the likelihood and severity of summer heatwaves is expected to rise – and so too is the number of heat-related summer deaths. For example, a recent report by the Lancet Countdown on Health and Climate Change project – an annual review of the scientific evidence of climate change’s effect on human health – found that the number of vulnerable people exposed to heatwaves is already increasing by millions.
Attribution studies are increasingly able to link rising global average temperatures with the frequency and severity of heatwaves, and even heatwave deaths. A study from 2016, for example, found that hundreds of deaths in London and Paris during the 2003 European summer heatwave could be attributed to the impact of climate change.
The new study, published in Science Advances, estimates the future heat deaths in 15 US cities under different levels of warming. The researchers compare the two warming limits enshrined in the Paris Agreement – 1.5C and 2C above pre-industrial levels – with the estimated 3C of warming that existing worldwide mitigation commitments would amount to.
Using data on daily mortality and temperature data for 1987-2000, the researchers identified the “exposure-response” relationship between temperature and heat-related deaths for each city. This essentially describes how the risk of death relates to temperature.
Typically, the risk of death is highest in very cold and very hot conditions. Somewhere in between will be a “minimum mortality temperature” (MMT) where the number of heat-related deaths is at its lowest. The lowest MMT of the cities studied in St Louis in Missouri at 15C, while the highest is 34.5C in Phoenix, Arizona.
Applying these observed relationships between temperature and heat-related deaths in climate model simulations, the researchers projected the number of deaths under each level of warming. They focus on “1-in-30-year heat-related deaths” – the annual number of people dying from heat where that year is the warmest in 30 years.
“We’ve assumed no adaptation, we’ve kept global population to be the same, we’ve kept the relationship between mortality and temperature to be the same – so that the only difference between these worlds would be temperature.
“We know that there are many factors that would affect future level of mortality and temperature-related mortality, but we’re asking the question of how global mean temperature rise – the level of global mean temperature rise, or difference – would affect mortality, and only this factor.”
In the video clip below, recorded at the American Geophysical Union Fall Meeting last year, Lo explains her study to Carbon Brief.
The chart below shows the projected increase in heat deaths for warming of 1.5C (dark blue), 2C (blue) and 3C (red) compared to present day (2006-15) for a 1-in-30-year heat event.Additional annual heat deaths in 15 US cities for a 1-in-30-year heat event, compared to 2006-15, for a 1.5C (dark blue), 2C (blue) and 3C (red) warmer world. Whiskers show 2.5-97.5% uncertainty range. Data provided by Eunice Lo. Highchart by Carbon Brief.
The results show an increasing number of heat-related deaths as the climate warms. At 1.5C, the study estimates between 35 and 779 additional annual deaths, depending on the city. For 2C, this increases to 70-1,515, and then at 3C to 139-3,495.
The results highlight the benefits of meeting the limits set out in the Paris Agreement, says Lo:
“Our main finding is, basically, for most of our studied cities, if we mitigate more – so if we increase our climate action to meet the 2C target – then fewer people will die from heat. But this level of mortality – heat-related mortality – would be substantially even lower if we mitigate to 1.5C of warming. So meeting the Paris Agreement’s targets – especially the 1.5C target – would be substantially beneficial to the population in the US.”
New York City stands out with the most to gain from limiting warming, the paper says:
“New York City…could see 1,980 1-in-30-year heat-related deaths avoided in the 2C warmer world relative to the 3C warmer world under the assumption of constant population. If the 1.5C world is realised, 2,716 of 1-in-30-year heat-related deaths could be avoided, relative to 3C.”
This is partly because New York City has the largest population of all the cities that the team studied, says Lo, which means it is likely to have more people who are vulnerable during heatwaves.
Similarly, the second and third most populous cities in the US – Los Angeles and Chicago – see substantially lower numbers of projected heat deaths under stricter warming limits.
The chart below shows the results on a relative scale, where the number of deaths are estimated per 100,000 of population. With the data presented in this way, the cities of Miami and Detroit see the largest reductions in heat deaths with lower warming levels.Additional annual heat deaths per 100,000 of population in 15 US cities for a 1-in-30-year heat event, compared to 2006-15, for a 1.5C (dark blue), 2C (blue) and 3C (red) warmer world. Whiskers show 2.5-97.5% uncertainty range. Data provided by Eunice Lo. Highchart by Carbon Brief.
There are some cases where the results don’t show clear differences at each warming levels the study notes. For example, in Atlanta, San Francisco and St Louis, the increases in heat deaths at 2C and 3C are statistically similar.
The paper also finds that some of the future 1-in-30 year maximum temperatures in these cities “may be hotter than what’s been observed in the last 30 years”, says Dr Vijay Limaye, a climate change and health science fellow at the US Natural Resources Defense Council science centre. Limaye, who wasn’t involved in the research, tells Carbon Brief:
“We may be literally off the charts in terms of unprecedented, widespread human exposure to insufferable heat if we don’t meet the challenge of limiting carbon pollution.”
The projected number of avoided deaths from limiting global temperature “may actually be underestimated”, says Limaye, because the study does not take into account future population growth.
The research also assumes that the existing relationship between temperature and heat-related deaths remains constant. This could change in the future as it has done over past decades. For example, adaptation measures could help reduce the future health burden of extreme heat. However, this is “not a given” says Limaye:
“For example, we see present-day access and affordability issues with air conditioning. We’re in new territory as public health scientists, and it’s not clear that this sobering picture even represents the full magnitude of the threat posed by deadly heat.”
The results draw attention to the raised health risks of global warming beyond the Paris limits, says Lo. This is particularly relevant as existing commitments by governments to cut emissions, known as “Nationally Determined Contributions” (NDCs), need to be ramped up in order to hold warming to 1.5C or 2C, she concludes:
“One of the motivations of this work is that the next round of NDC submissions for the Paris Agreement will happen in the year 2020, and we hope that our results could motivate increasing climate action internationally in these NDCs.”
This Article Originally Appeared On Carbon Brief
About The Author
Robert McSweeney is science editor. He holds an MEng in mechanical engineering from the University of Warwick and an MSc in climate change from the University of East Anglia. He previously spent eight years working on climate change projects at the consultancy firm Atkins.
Life After Carbon: The Next Global Transformation of Cities
by Peter Plastrik , John Cleveland
The future of our cities is not what it used to be. The modern-city model that took hold globally in the twentieth century has outlived its usefulness. It cannot solve the problems it helped to create—especially global warming. Fortunately, a new model for urban development is emerging in cities to aggressively tackle the realities of climate change. It transforms the way cities design and use physical space, generate economic wealth, consume and dispose of resources, exploit and sustain the natural ecosystems, and prepare for the future. Available On Amazon
by Elizabeth Kolbert
Over the last half-billion years, there have been Five mass extinctions, when the diversity of life on earth suddenly and dramatically contracted. Scientists around the world are currently monitoring the sixth extinction, predicted to be the most devastating extinction event since the asteroid impact that wiped out the dinosaurs. This time around, the cataclysm is us. In prose that is at once frank, entertaining, and deeply informed, New Yorker writer Elizabeth Kolbert tells us why and how human beings have altered life on the planet in a way no species has before. Interweaving research in half a dozen disciplines, descriptions of the fascinating species that have already been lost, and the history of extinction as a concept, Kolbert provides a moving and comprehensive account of the disappearances occurring before our very eyes. She shows that the sixth extinction is likely to be mankind's most lasting legacy, compelling us to rethink the fundamental question of what it means to be human. Available On Amazon
Climate Wars: The Fight for Survival as the World Overheats
by Gwynne Dyer
Waves of climate refugees. Dozens of failed states. All-out war. From one of the world’s great geopolitical analysts comes a terrifying glimpse of the strategic realities of the near future, when climate change drives the world’s powers towards the cut-throat politics of survival. Prescient and unflinching, Climate Wars will be one of the most important books of the coming years. Read it and find out what we’re heading for. Available On Amazon
From The Publisher:
Purchases on Amazon go to defray the cost of bringing you InnerSelf.comelf.com, MightyNatural.com, and ClimateImpactNews.com at no cost and without advertisers that track your browsing habits. Even if you click on a link but don't buy these selected products, anything else you buy in that same visit on Amazon pays us a small commission. There is no additional cost to you, so please contribute to the effort. You can also use this link to use to Amazon at any time so you can help support our efforts.