One of the biggest concerns that people have about climate change is how it might affect human health. What are the current and projected future health impacts of climate change? Who is at risk? What can be done to reduce those impacts and risks?
Climate change affects human health in three ways:
These effects of climate change do not act in isolation, however; environmental, social, and health system factors modify these impacts substantially.
This chart from the IPCC (it's an oldie but goodie from 2007) demonstrates the varying levels of confidence of several impacts on human health. We see red arrows of varying length pointing toward the left to denote negative impacts while we see blue arrows of varying lengths pointing to the right to denote positive impacts. What do you notice, though, about the size and frequency of the negative impact arrows vs. the positive impact arrows? (That's right! The negative impacts far outweigh the positive ones.)
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 [2]. 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 [4] 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 [5]).
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.
Indirect impacts of climate on human health are ones in which the human body is not immediately affected by the climate system but instead feels the delayed impacts through some intermediary. Indirect impacts affect many more people in many more ways than the direct impacts. The list is long and includes, among others:
Several food-borne pathogens are spreading due to climate change. Depending on the crop type, drought and excess moisture encourage crop pests and spread molds. Climate-driven rusts, blights, and rots are devastating already stressed crops and thereby indirectly affecting human health through decreased food security.
But it's not just our crops falling ill from increased pathogens in a changing climate. Instances of some types of pathogens that make their way to people are also on the rise. The US Global Change Research Program's Climate and Health Assessment from 2016 describes some of these pathways and consequences (and in their bulleted list [14], they include ample citations to support each bullet point - I'm linking out to that directly in hopes the links there are updated as necessary):
Water-borne diseases are closely related to weather and climate. Cholera, cryptosporidiosis, and several other significant diseases are spread by fecal contamination of water supplies and are often closely associated with floods and heavy downpours. In other cases, drought can concentrate disease pathogens in pools and low flows. Climate change is causing increased intense rainfall events in many parts of the world and drought in others; it is not surprising that water-borne illness is a growing problem in those areas with the most extreme changes. The key to understanding the spread of water-borne illness in a changing climate is exposure. As this image shows, various factors (all from human activity) are increasing our exposure to these illnesses.
Disease vectors, such as mosquitos and ticks, are moving into new areas as warmer, wetter climates push poleward and upslope. The spread of malaria and dengue fever, for instance, is believed to be at least partly due to mosquitos expanding their range with the changing climate.
Click through this series of maps illustrating the projected expansion of mosquitos carrying Aedes-borne viruses (dengue fever* and Zika among them). These projections are based on an RCP (representative concentration pathway [17]) of 8.5 which is really a worst-case scenario in which we continue on with our business as usual practices and fail to mitigate climate change. So, with any luck, this won't happen! But, you can also see a set of projections based on a more plausible RCP with the original paper (Ryan et al., 2019 [18]). These projections demonstrate the rapid increase in exposure for highly populated areas, some expansion into new areas - meaning newly vulnerable populations.
*In 2019, countries across tropical Asia saw higher than usual instances of dengue fever.
Let's take a look at another vector, ticks. Look at the massive growth in reported cases of Lyme Disease [22] between 1996 and 2014. Many of you live in Pennsylvania or surrounding states, so you're likely all too familiar with ticks and Lyme Disease. Most of us have a story or two of pulling a deer tick off ourselves, our children, or our pet. I've spared you a close-up image of a deer tick on this page, you're welcome.
Rodents and their fleas are also a concerning disease vector with changing distributions in a changing climate. For example, Hantavirus borne by fleas on deer mice is closely linked to the ENSO cycle in the US Southwest (Hjelle and Glass, 2000 [24]), and evidence points to climate-related distribution changes in Europe of Hantavirus borne by other rodents (European Center for Disease Prevention and Control, n.d. [25]). In Brazil, warmer temperatures mean an increased expansion of sugarcane production. Rodents (particularly deer mice) find sugarcane quite tasty and estimates suggest that this combination of increased sugarcane production and warming temperatures could expose an additional 20% of Brazilians [26] to this potentially fatal virus.
Sometimes, when I'm having a conversation about climate change (as one does!), I hear people talk about our greenhouse gas emissions as pollutants. I've personally never really thought of them that way (even though, perhaps I should because they do overlap), because I tend to think of air pollution as particulate matter - soot, big puffs of black exhaust from the back of a truck, things like that. Greenhouse gas emissions seem categorically different to me - like secret pollutants we can't see. However, it's important to understand that regardless of how you conceive of GHGs and pollutants, our GHG emissions are affecting the more traditional air pollutants in ways it's important for us to understand.
Air quality and its effect on human health is in large part a function of the weather, which creates conditions that promote or depress the formation, concentration, deposition, dispersion, and transport of pollutants. Changing climate means changes in location, timing, and intensity of air pollution events. Ground-level ozone, the most noxious constituent of photochemical smog, is associated with a host of health problems and is strongly and positively correlated with temperature and solar radiation; increases in temperature and longer summer seasons correspond to increases in general ozone concentrations and the number of days violating air quality standards. Here's a short EPA podcast from 2016 called The Future of Breathing: Connecting Air Quality and Climate Change [27] I'd like you to spend 2 minutes on (or read its transcript).
Particulate matter (PM) has even greater health effects than ozone; this pollutant is also linked to temperature and humidity in its formation. Forest fires also release many particulate air pollutants and toxic gases and are known to affect health. Forest fires are on the increase worldwide and forecast to escalate dramatically in the future.
Let's circle back to thinking about vulnerability and how people might experience this type of impact of a changing climate differently than those around them. The American Lung Association [28] estimates 26 million people in the US are living with asthma. Poor air quality is just one potential indirect impact on human health that affects people with asthma more acutely.
One of the biggest climate impacts on human health is through seasonal allergens. Over the past few decades, spring is coming earlier and fall is ending later in the Northern Hemisphere, increasing the length of the allergy season. (Do you hear the collective groan of the roughly 30% of the population who suffer from seasonal allergies?) Changing distributions of plants and molds (thanks to extreme precipitation events and changing temperature patterns) are causing the spread of allergens into areas where they did not exist earlier. There is also some evidence that the rising atmospheric CO2 concentration is fertilizing some allergen-rich species, like ragweed (Albertine et al., 2014 [30]).
What do you notice about this map? The northern latitudes of the US and the western part of the country are seeing rapidly expanding numbers of frost-free days relative to the southern US. It's just another reminder that while impacts are global in nature, they materialize very differently across smaller geographic scales.
For this week's lesson, let's focus specifically on the effects climate change impacts can have on one's mental health. This is separate from thinking about the mental health implications associated with people worrying about climate change in general (which is a rapidly growing issue). We'll probably have a chance to tackle that in Unit 3: Solutions.
This area seems a bit understudied compared to the more obvious impacts and isn't discussed as much publicly. Flooding, droughts, Lyme Disease, asthma - we've talked about a lot of potential issues connected to climate change that might seem more connected. But, the mental health implications of living through many of these impacts is of serious consequence and worth our time to better understand.
Mental health is inextricably linked to physical and community health (see those bidirectional arrows between the physical, mental, and community symbols - it's all connected!).
It is important to recognize that climate change is neither the primary driver of human health today nor will it be in the future. Beyond genetics, access to these three factors are fundamental to the good health of an individual and a society.
In summary, individuals who live in developed countries generally have better access to safe water and sanitation, good nutrition, and health care. People who live in the least-developed nations often have unsafe water and poor sanitation, inadequate nutrition, and little access to health care. Therefore, with or without climate change, health outcomes vary based on a person's country of residence and its level of development.
Links
[1] https://www.ipcc.ch/report/ar4/wg2/human-health/
[2] https://www.preventionweb.net/files/46796_cop21weatherdisastersreport2015.pdf
[3] https://www.undrr.org/publication/human-cost-weather-related-disasters-1995-2015
[4] https://www.globalchange.gov/browse/indicators/us-heat-waves
[5] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4202759/
[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
[13] http://www.fao.org/tempref/docrep/fao/011/i0378e/i0378e.pdf
[14] https://health2016.globalchange.gov/food-safety-nutrition-and-distribution#table-125
[15] http://climateandhealthalliance.org/uncategorized/climate-change-and-food-safety/
[16] https://health2016.globalchange.gov/water-related-illness
[17] https://www.ipcc-data.org/guidelines/pages/glossary/glossary_r.html
[18] https://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0007213
[19] https://www.npr.org/2019/07/31/747012629/bangladesh-reports-more-than-13-000-dengue-cases-in-july?fbclid=IwAR0NQWLtp3v2EGO_8zHF2ySpBF1-5MHk6DUqZ0XU7WWWN7tXAhoSRXSwp7c
[20] https://www.straitstimes.com/asia/se-asia/philippines-declares-national-alert-after-456-dengue-deaths
[21] http://outbreaknewstoday.com/peak-dengue-season-in-singapore-8000-cases-5x-last-years-number-26932/
[22] https://www.cdc.gov/lyme/index.html
[23] https://www.cdc.gov/lyme/datasurveillance/index.html?CDC_AA_refVal=https%3A%2F%2Fwww.cdc.gov%2Flyme%2Fstats%2Findex.html
[24] https://academic.oup.com/jid/article/181/5/1569/2191142/
[25] https://www.ecdc.europa.eu/en/climate-change/climate-change-europe/rodent-borne-diseases
[26] https://www.reuters.com/article/us-brazil-climatechange-health/brazil-risks-rodent-borne-hantavirus-rise-due-to-sugarcane-climate-change-scientists-idUSKBN1A52IV
[27] https://19january2017snapshot.epa.gov/research/science-bite-podcasts_.html#future
[28] https://www.lung.org/about-us/blog/2019/05/asthma-and-climate-change.html
[29] https://www.epa.nsw.gov.au/about-us/publications-and-reports/state-of-the-environment
[30] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4221106/
[31] https://nca2014.globalchange.gov/report/our-changing-climate/frost-free-season
[32] https://s3.amazonaws.com/climatehealth2016/low/ClimateHealth2016_08_Mental_Health_small.pdf
[33] https://www.cdc.gov/healthywater/global/wash_statistics.html
[34] https://www.flickr.com/photos/24647935@N06/4103407163
[35] https://www.flickr.com/photos/24647935@N06
[36] https://creativecommons.org/licenses/by-nc-sa/2.0/?ref=ccsearch&atype=html
[37] https://www.who.int/news-room/detail/11-09-2018-global-hunger-continues-to-rise---new-un-report-says
[38] https://www.worldhunger.org/world-hunger-and-poverty-facts-and-statistics/
[39] https://ourworldindata.org/hunger-and-undernourishment
[40] https://creativecommons.org/licenses/by/4.0/
[41] https://www.theatlantic.com/health/archive/2016/11/cuba-health/508859/
[42] http://worldpopulationreview.com/countries/life-expectancy/
[43] https://ourworldindata.org/the-link-between-life-expectancy-and-health-spending-us-focus
[44] http://apps.who.int/gho/data/node.sdg.tp-1?lang=en
[45] https://creativecommons.org/licenses/by-nc-sa/3.0/igo/