Tag: heat waves

Global Science Report: Health Effects of Global Warming

The impact of global warming on temperature-induced human mortality has long been a concern, where it has been hypothesized that rising temperatures will lead to an increase in the number of deaths due to an increase in the frequency and intensity of heat waves. Others claim that rising temperatures will also reduce the number of deaths at the cold end of the temperature spectrum (fewer and less severe cold spells), resulting in possibly no net change or even fewer total temperature-related deaths in the future.

The largest study—by far—on temperature-related mortality was published by Gasparrini et al. in the journal Lancet in 2015. They examined over 74 million (!) deaths worldwide from 1985 to 2012 and found that the ratio of cold-related to heat-related deaths was a whopping 17 to 1. Moreover, the temperature percentile for minimum mortality was around the 60th in the tropics and “80–90th” in the temperate zones. Based upon real-world data, it is obvious that global warming is going to directly prevent a large number of deaths.

One of us (Michaels) co-authored a peer-reviewed literature article showing that as heat waves become more frequent, heat-related deaths decrease because of adaptation. Given that our cities are heating up on their own—without needing a push from greenhouse gases—under our hypothesis, heat-related mortality should be dropping, which it is.

Heat-related Death Projections Don’t Square with Observations

Global Science Report is a feature from the Center for the Study of Science, where we highlight one or two important new items in the scientific literature or the popular media. For broader and more technical perspectives, consult our monthly “Current Wisdom.”

We realize that we are 180° out of sync with the news cycle when we discuss heat-related death in the middle of Northern Hemisphere winter, but we’ve come across a recent paper that can’t wait for the heat and hype of next summer.

The paper, by Arizona State University’s David Hondula and colleagues, is a review of the recent scientific literature on “human health impacts of observed and projected increases in summer temperature.”

This topic is near and dear to our hearts, as we have ourselves contributed many papers to the scientific literature on this matter (see here).  We are especially interested in seeing how the literature has evolved over the past several years and Hondula and colleagues’ paper, which specifically looked at findings published in the 2012-2015 timeframe, fills this interest nicely.

Here’s how they summed up their analysis:

We find that studies based on projected changes in climate indicate substantial increases in heat-related mortality and morbidity in the future, while observational studies based on historical climate and health records show a decrease in negative impacts during recent warming. The discrepancy between the two groups of studies generally involves how well and how quickly humans can adapt to changes in climate via physiological, behavioral, infrastructural, and/or technological adaptation, and how such adaptation is quantified.

Did you get that? When assessing what actually happens to heat-related mortality rates in the face of rising temperatures, researchers find that “negative impacts” decline. But, when researchers attempt to project the impacts of rising temperature in the future on heat-related mortality, they predict “substantial increases.”

In other words, in the real world, people adapt to changing climate conditions (e.g., rising temperatures), but in the modeled world of the future, adaptation can’t keep up.