Extreme Temperatures

this graph was created in OurDataWorld:

Think about someone dying from extreme temperatures. You probably pictured someone passing out from heat stroke or dying from hypothermia.

But this is not how most people die from “heat”. They die from conditions such as cardiovascular or kidney disease, respiratory infections, or diabetes.1

Almost no one has “heat” or “cold” written on their death certificate, but sub-optimal temperatures lead to a large number of premature deaths. As we’ll see later, researchers estimate that it kills several million every year.

Older populations are usually most vulnerable to extreme temperatures. Most deaths occur in people older than 65. It’s important to consider what "death" means here and how deaths from extreme temperatures might compare to other causes. Being too hot or cold can increase our risk of developing certain health conditions or worsen existing ones. It can thereby lead to an earlier death than would have occurred if the temperatures were “optimal”.

How much time do hot or cold conditions take off someone’s life? It’s difficult to give precise estimates. One method that researchers often use is to look at excess death rates — which measure how many more people die in a given year compared to an “average” year — in a particularly warm or cold year. Looking at patterns of excess deaths gives some indication of whether temperature-related deaths were “brought forward” significantly or not.

A study by Nirandeep Rehill and colleagues examined death patterns in the United Kingdom over 50 years.2 It found that most cold-related deaths were among people who would not have died in the next 6 months. A later study looked at the impacts of high and low temperatures across a much larger sample of countries.3 It found that most temperature-related deaths reduced lifespans for at least one year. Most people died at least one year earlier, although there would be some that did lose less than this.

In this article, I will examine how many people die from heat and cold each year and how researchers estimate these numbers. In a follow-up article, I’ll look at how these risks could change in the future due to climate change.

A quick note on terminology: I will use the term “temperature-related deaths” from this point forward to refer to the combination of deaths from heat and cold conditions. When I use the term “heat”, I mean warm or hot.