Date:21 June 2017
As temperatures rise, so too does the risk of heat-related death. Right now, about 30 percent of the world’s population is exposed to deadly temperatures at least 20 days out of the year. By 2100, that number could reach 74 percent if greenhouse gas emissions continue to rise, or 48 percent with drastic cuts to global emissions.
The findings have been published in Nature Climate Change. ResearchGate spoke with Iain Caldwell, one of the study’s authors, to learn more.
ResearchGate: What did your study find?
Iain Caldwell: Our study found that the vast majority of past heat-related deaths were associated with periods of high temperatures and high humidity, and that such deadly conditions could become much more common in the future, particularly in the tropics and if current carbon emissions are not reduced considerably.
RG: How did you determine this?
Caldwell: To find out when and where people had died from heat in the past we searched for all past studies on heat-related death to determine which conditions best discriminated between the lethal and non-lethal events: a combination of average daily temperature and average daily humidity. We were also able to identify a threshold in these two conditions, beyond which the combination and temperature has been lethal in the past.
The next step was to find out when and where these deadly combinations of temperature and humidity have occurred and when they might occur in the future. We formed climate models of three possible future climate scenarios: one with no change in carbon emissions, one with moderate mitigation, and one with strong mitigation. We found that there already seems to be an increase in the number of deadly days since the past and that those deadly conditions could increase substantially in the future, particularly if we do nothing to reduce our impacts on climate change.
RG: What makes high temperatures so deadly?
Caldwell: High temperatures (and high humidity) can become deadly when the body produces or absorbs more heat than it can release. One of the main ways that the body releases heat is through sweating. However, when it is particularly hot and humid outside, the body cannot release as much heat as it produces, elevating the core body temperature. When the core body temperature gets hot enough it can create problems for many of the body’s organs and, in some cases, the organs can malfunction and eventually lead to death.
RG: Who is most at risk of heat-related death?
Caldwell: At highest risk are the elderly and anyone with existing conditions that already put a strain on the same organs that are affected by heat stress.
RG: Which geographic areas are most affected?
Caldwell: We predict that people living in the tropics will experience more frequent and more severe deadly heat than the rest of the world. Unfortunately, many of the countries that could be hardest hit by these changes are also some of the poorest, whose citizens may have less access to air conditioning or hospital facilities during these times of high heat stress.
RG: What can individuals do to minimise their risk?
Caldwell: In places where there are early warning systems in place, individuals can prepare for unusually hot and humid days by limiting their exposure to the conditions, for example by staying indoors in cooler areas. After the extreme 2003 European heatwave that killed more than 70,000 people, cities like Paris developed such early warning systems.
RG: What can be done on a societal level to address this problem?
Caldwell: The underlying problem is that the climate is changing, and as a society we can limit how much we are impacting those changes. Policy changes that aim to reduce carbon emissions are obviously needed but, we can also all make personal decisions that can make a difference. Individuals can also do their part to minimise the impacts of these and other climatic changes by reducing their own carbon footprint. There are several carbon calculators that anyone can use to calculate what their personal impacts are on global carbon emissions. Although it may seem like a very small change, personal decisions like how much to drive can have a large effect if enough people make those small decisions to limit their impact.
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