Global warming's heat death toll

11 June 2019

Interview with 

Eunice Lo

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Scientists from the University of Bristol are saying that limiting extreme global warming could prevent thousands of people from dying from the effects of high temperatures. They claim that - to achieve this - every country needs to ramp up its climate commitments to reach the Paris agreement’s target of limiting the global temperature increase to 1.5 degrees Celsius. By looking at cities in the US, this is the first study to examine the human mortality cost if global warming goes above two degrees. Phil Sansom spoke to the paper’s lead author Eunice Lo...

Eunice - Hundreds to thousands of heat-related deaths could be avoided if we limit global warming to 1½  degrees Celsius. It's a substantial number based on the current climate commitments we are probably heading towards 3 degree warming, so this is way higher than the 1½ or 2 degrees in the Paris Agreement. And so our study looked at what would be the public health benefits of increasing our climate action to achieve the Paris Agreement’s goal.

Phil - So what exactly did you do?

Eunice - We have data from the period of 1987 to 2000 of daily temperature and also daily counts of mortality of 15 cities in the United States.

Phil - All US cities?

Eunice - Yes, all US cities, and they're all rather populated or they're major US cities. Part of the funding for this paper was from the Union of Concerned Scientists in the United States, and also the United States have more reliable health data and weather station data than many other places in the world, so that was another reason why we chose to study the United States.

Phil - Okay. So you had this data from the 15 cities, what did you do with it?

Eunice - We found relationships between temperature and mortality.  So we were able to then say, for example, at 25 degrees Celcius in New York City, what is the mortality risk? And so with this relationship we combined it with future climate projections to estimate future mortality levels.

Phil - It's as simple as that, you could just find the relationship and then apply it to what we know about future temperatures?

Eunice - There's a lot more complicity in the modelling side of things. We have created scenarios that describe the 1½  degree, 2 degree, and 3 degree’s world to create the results. We have found that hundreds and thousands of heat-related deaths that would occur in the current trajectory of 3 degree world that could be avoided if we limit global warming to 1½  degrees. So essentially, this many deaths could be prevented if we increase climate action.

Phil - I guess it seems like a lot in itself, but in a city of maybe millions of people a thousand people isn't that many. Do you think that’s the full picture?

Eunice - I do think this is a significant result because, obviously, we wouldn't want huge increases in heat-related mortality in a warming world, and hundreds to thousands of people per city in a certain year is kind of a lot in my opinion.

Phil - Are there any other factors that weren't included that could potentially make things easier or could make things worse?

Eunice - Yeah, yeah. We have based our study on current population and not included any population growth in the future, and we also haven't included an ageing population in our study. People who are 65 years old or above are more susceptible to heat-related mortality than younger people. So these factors could increase our estimates in terms of the number of heat-related deaths. But, on the other hand, if there were future adaptation methods for example, if there is better healthcare or there's an improved early warning system for extreme high temperatures or heat waves, then these adaptation measures could also reduce the number of heat-related deaths.

And so the takeaway message here is that regional adaptation is also very important and could prevent exacerbation of, or large increases in heat-related mortality in the future.

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