Direct impacts of climate on human health occur when the human body is physically stressed or injured immediately by some element of the climate system.
Examples of direct impacts include:
Remembering that we're looking at the direct impacts on human health right now, we're thinking about the immediate impact events such as hurricanes, wildfires, droughts, and floods have on people's health. But how many people are affected by these various extreme weather events?
In 2015, the Centre for Research on the Epidemiology of Disasters (CRED) and the UN's Office for Disaster Risk Reduction (UNISDR) published The Human Cost of Weather Related Disasters 1995-2015 [1]. The timing of this report wasn't accidental - it was intended to help inform the urgency of the then-upcoming Paris climate negotiations producing meaningful targets for GHG mitigation. The two infographics below show the numbers of people affected and killed by weather-related disasters in 1995-2015.
The US Global Program on Climate Change [3] defines a heat wave as, "a period of two or more consecutive days where the daily minimum apparent temperature (actual temperature adjusted for humidity) in a particular city exceeds the 85th percentile of historical July and August temperatures for that city". Heat waves have been more frequent and more intense in the last few decades. As the maps and graphs below illustrate, not only are heat waves getting more frequent, the seasons in which they occur are getting longer.
But maybe when you look at these maps you think, "Ok, we're having more heat waves - that might be uncomfortable, but it's not actually affecting my health? Let's take a closer look. Remember in Lesson 3 when we were looking at vulnerability to climate change impacts and we talked about the 2003 heat wave in Europe and the almost 15,000 people in Paris who died (not to mention the 55,000 other people who died across Europe in that heat wave )?
Vulnerability plays a huge role in determining how a person or group of people experience climate change impacts. And yes, for many Americans, more heat waves are nothing more than an inconvenience. Perhaps I don't have air conditioning and will be uncomfortable. But maybe I have the resources (adaptive capacity) to minimize my exposure by staying with a family member with air conditioning, buying some fans, or spending the hottest parts of the day outside my home. My exposure might be similar to someone else's but as a healthy adult with reasonable resources, my sensitivity is lower and my adaptive capacity higher, thereby making me less vulnerable. While we saw that many of those deaths in Paris were elderly women, it's not just who you are that can make you vulnerable, but also what you do for a living. People who work outdoors have an obviously higher exposure to heat wave events and are therefore also more vulnerable to the direct health impacts those events bring (Xiang et al., 2014 [4]).
Let's take a look at a project in the Bronx to help identify residents most vulnerable to heat waves and the adaptation measures they're implementing to keep folks safe during extreme heat events.
As heat wave frequency and intensity increase in a changing climate, heat wave mortality also rises. This map (a) and graph (b) from that 2003 European heat wave shows the increased mortality across France that summer (this is calculated based on the mortality you'd expect under normal conditions) as well as the mean daily temperature in 2003 and its corresponding daily mortality compared to those values for the 1999-2002 time period.
NOAA's Billion-Dollar Weather and Climate Disaster Database [6] (yep, that's really a thing) includes four drought/heat wave incidents since 1980 in its list of deadliest events. It is interesting to note that heat wave mortality varies with location: in Russia, South Asia, and Southeast Asia, deaths were primarily in rural areas; in the US, deaths were almost exclusively in urban areas; and in southern Europe, deaths were in both rural and urban areas.
Wait. We just spent all that time talking about all of these more frequently occurring and more severe heat waves. Extreme cold? Although very cold days, very cold nights, and total frost days have declined over the past few decades, cold waves are still a problem and more recent studies are exploring the link between a changing climate and periods of extreme cold weather. This issue got a fair bit of attention in the early winter months of 2019, as the eastern US found itself subject to another polar vortex event. Cold weather is often a favorite talking point for overly simplistic climate denial, but in reality, the connection is much more complex and cold weather is anything but an indication that climate change isn't real. A changing climate is destabilizing the jet stream and allowing Arctic weather to dip down to lower latitudes than it otherwise would here in the US. Luckily, many popular news outlets tried to get in front of this by offering explanations of how climate change and cold snaps are related (see National Geographic's Why Cold Weather Doesn't Mean Climate Change is Fake [7], Climate Reality Project's Yes It's Cold, and Yes Our Climate is (Still) Changing [8], or Scientific American's Why Global Warming Can Mean Harsher Winter Weather [9]).
Much like heat waves, vulnerability is determined in a large extent to one's exposure. The most vulnerable among us are those people without adequate housing or reliable heat sources. People with existing health conditions or who are very young or very old are more sensitive. This NY Times article, Extreme Cold Weather Spreads East [10], offers a glimpse at many of the human health issues authorities were dealing with during this cold wave event in early 2019.
We'll be looking at extreme weather events in more detail in Impacts on Earth: Climate and Weather [12], but let's talk a bit about the specific human health dimensions of extreme weather. Obviously, heat waves and cold waves are forms of extreme weather too, but we tend to break those out separately from storms, floods, and droughts (though we can certainly group droughts and heat waves together). This is a recurring theme with the topics we're discussing this semester - they're all inextricably linked, and there's never a good starting point or logical progression.
Links
[1] https://www.preventionweb.net/files/46796_cop21weatherdisastersreport2015.pdf
[2] https://www.undrr.org/publication/human-cost-weather-related-disasters-1995-2015
[3] https://www.globalchange.gov/browse/indicators/us-heat-waves
[4] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4202759/
[5] https://www.ipcc.ch/report/ar4/wg2/human-health/
[6] https://www.ncdc.noaa.gov/billions/events
[7] https://www.nationalgeographic.com/environment/2019/01/climate-change-colder-winters-global-warming-polar-vortex/
[8] https://www.climaterealityproject.org/blog/yes-cold-yes-our-climate-still-changing
[9] https://www.scientificamerican.com/article/earthtalks-global-warming-harsher-winter/
[10] https://www.nytimes.com/2019/01/31/us/weather-polar-vortex.html
[11] https://www.noaa.gov/multimedia/infographic/science-behind-polar-vortex-you-might-want-to-put-on-sweater
[12] https://www.e-education.psu.edu/geog438w/node/614