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The Consequences of Anthropogenic Climate Change on Public Health

Thomas Charles Roland

Department of Natural Sciences, California State University, San Bernardino

HSCI 6230: Environmental and Occupational Health

Professor Vandyke

February 13, 2021

Introduction

With each passing decade, public health is increasingly faced with new emerging

diseases and increased natural disasters that threaten the health and safety of the public. Since

garnering meaningful attention in 1988, climate change has worsened and reached a threshold

that threatens the health of the world’s entire population (Butler, 2018). The effects of climate

change have become so severe that it is one of the greatest threats humanity currently faces. It is

important to note that while climate change is naturally occurring in the expansive history of our

planet, this will be the first time in history that humans are responsible for the changes we are

currently experiencing. If humanity continues to traverse this path, the effects of climate change

on public health and the world will be catastrophic. To fully understand the magnitude of the

situation, it is necessary to comprehend the evidence for the human connection with climate

change. Before the start of the industrial revolution, the estimated carbon dioxide levels in the

atmosphere were around 280 parts per million (ppm) (NASA, 2021). In the years following the

industrial revolution, we have observed a continual increase in carbon dioxide levels so severe

that we have reached around 415ppm with no indication of decreasing (NASA, 2021).

Additionally, compared to the preindustrial era, the mean global temperature has increased by

one centigrade (Rocklöv & Dubrow, 2020). The effects from this one-degree increase have been

significant. Rocklöv and Dubrow (2020) report that the one-degree increase in temperature has

resulted in an increase in the number of warm days, a decrease in the number of cool nights and

days, more frequent extreme heat events, decreased snowfall, and rising sea levels. At our

current rate, many scientists estimate that we will not be able to mediate the aversive effects of

our actions and our inaction to address these problems. The human population is dependent on

the environment for clean air, clean water, shelter, and food. The rapid increase in warming
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trends around the globe and resultant shifts in climate threatens this delicate dependency and

currently stands to harm the progress made in public health over the years. In this paper, we

present the most significant findings of the effects of climate change on global health and how

these effects will continue to shape our future. These effects include, but are not limited to,

vector-borne disease, human health both neurologically and immunologically, and the increase in

incidence of extreme heat events.

Vector-Borne Diseases

One of the most damaging effects climate change has and will continue to have on public

health is the increased warming trends across the globe. Warmer temperatures and longer

summers have resulted in increased reproduction of insect vectors. Vectors are organisms that

feed on blood and are capable of transmitting infectious pathogens from an animal host or

infected human to an uninfected human. Concerningly, humans serve as the primary host for

some of the deadliest vector-borne diseases like malaria, dengue, and Zika virus. Currently, the

World Health Organization (WHO) reports that vector-borne diseases constitute around 17% or

more of infectious diseases, resulting in more than 700,000 deaths yearly. As a result of

increased anthropogenic warming, the numbers are expected to increase. Climate change affects

vector-borne diseases through increased temperatures. These increased temperatures affect

transmission dynamics, geographic spread, and resurgence of vector-borne diseases through

multiple pathways (Rocklöv & Dubrow, 2020). There is also substantial evidence to suggest that

as temperatures increase, vector abundance and activity will increase (Cambell-Lendrum et al.

2015; Barrett et al., 2015). This increase is expected as arthropods and other vectors are

ectotherms. The warming from climate change also affects precipitation, and this has important

implications for disease vectors. Rocklöv and Dubrow (2020) report that that relationship
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between precipitation and vector quantity is quite complex and situation specific. On one hand,

increased rainfall has the capacity to increase vector reproduction sites, and on the other, drought

has the capacity to increase vector reproduction sites due to an abundance of rainwater collection

and storage in response to drought. Kovats et al. (2003) presented similar findings and explained

that drought in normally wet regions could potentially decrease flow velocity in brooks and

provide increased pools of stagnant water for mosquitoes to reproduce. Wu et al. (2016)

substantiate the findings in Rocklöv and Dubrow (2020) whereby the increase in temperature as

a result of climate change impacts vector distribution. Wu et al. (2016) found that temperature

affects the spatial-temporal spread of vectors. For example, as temperatures continue to increase,

insects in low latitude areas may seek new habitats in higher latitude regions and areas higher in

altitude, which then affects the geographical shift of diseases. Studies conducted in the early

2000s already demonstrated evidence early on of the effects that warmer temperatures have on

vector distribution. Harvell et al. (2002) found that warmer temperatures have resulted in a wider

distribution of diseases such as Lyme disease, malaria, plague, and dengue. Harvell et al. (2002)

found that most of the aforementioned diseases spread into areas of higher latitude, directly

following habitat amplification of ticks and mosquitoes. Consequently Bezirtzoglou et al. (2011)

reported a greater incidence of West Nile virus in some European countries, demonstrating the

disastrous effects of anthropogenic climate change on vector distribution early on. Wu et al.

(2016) also found that changes in precipitation due to climate change may impact vectors, thus

substantiating the claims made in Rocklöv and Dubrow (2020). These claims are further

substantiated by Hoshen and Morse (2004) where the researchers found larval development of

some mosquito vectors increases with rainfall and increasing temperature. While the influence of
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climate change on vector-borne diseases is becoming increasingly common in the literature,

more research is necessary to further the understanding of the link between the two.

Human Health: Neurological and Immunological

Anthropogenic climate change affects human health in various ways and has serious

implications that are being experienced currently and will continue to be experienced unless

action is taken. Climate change increases mean temperature, increases sea levels, and increases

the frequency of extreme weather events, which all have detrimental impacts not only on the

environment, but on human health. Climate change alters the quantity of clean drinking water,

changes the trajectory of diseases, and greatly impacts food production, all of which negatively

impact human health. Along with the broader effects that climate change has on human health,

research is demonstrating increasingly specific effects on human health. The brain is perhaps the

most important organ in humans and in most animals and research demonstrates that climate

change may have an effect on development of the central nervous system (CNS). Ruszkiewicz et

al. (2019) demonstrated from animal studies that temperature modulates brain development.

Additionally, Amiel et al. (2017) and O’Donnell (2018) demonstrated that temperature changes

as a result of climate change not only alter neuronal development but also brain organization.

Subsequent research by Pallotta et al. (2017) found that temperature was able to cause

differential expression of several genes involved in gonadal and neuronal differentiation in

Leopard Geckos. Changing atmospheric conditions that result from climate change have been

linked with increased neurological problems in humans. Scheidt et al. (2013) found that in the

German population, increases and decreases in temperature lead to more frequent reports of

migraines. Additionally, the brain is susceptible to many environmental contaminants that have

neurotoxic consequences. Metals such as mercury, manganese, arsenic, and lead, pesticides,
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organic pollutants, and other endocrine disruptive chemicals have been found to have negative

effects on the human body. The prevalence of these substances in the environment is due either

to a natural or anthropogenic source, and consequently, recycling and accumulation of these

substances is susceptible to climate change (Ruszkiewicz et al., 2019). Subsequently, the weather

exerts a heavy influence on the distribution and quantity of contaminants within the air, with

climate change presumably aiding in increasing the amount of air contaminants which are also

harmful to not only general health, but neurological health. Research demonstrates that climate

change has drastic effects on the immune systems of individuals. Climate change often worsens

the symptoms in individuals with a diagnosed allergic disease, especially those with asthma or

rhino conjunctivitis (Ray & Ming, 2020). According to the American Academy of Allergy

Asthma & Immunology (AAAAI), climate change affects the protein structure and production of

fungal spores and pollen. Additionally, the pollen seasons of grasses, weeds, and trees are

affected by climate change. These alterations in the duration and amount of pollen greatly affect

those with severe allergies. The increased intensity of the pollen season can be linked to the

increase of pollen. This increase in pollen production can be traced in part to the increased

greenhouse gases in the atmosphere. This results from increased carbon dioxide and reflexive

response in plant reproduction, thus an increase in pollen production (Ray & Ming, 2020). The

AAAAI also reports that greenhouse gases are harmful to the respiratory systems in individuals

with asthma and other conditions. Overtime, the increased greenhouse emissions contribute to a

decrease in lung function overtime and premature mortality. As climate change continues to

shape and disrupt our current environment, Ray and Ming (2020) explain that increased warming

due to climate change may result in more erratic immune responses and functioning. In Ming and

Ray (2019) a similar idea was explored whereby disruption in ecosystems exposes the human
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body to novel organisms. Findings from the Centers for Disease Control and Prevention (CDC)

support these claims. In the CDC’s surveillance data there has been an increase in the prevalence

of immunological disorders over the last few decades (CDC, 2018). Further research will

ultimately be required in order to fully understand the relationship between anthropogenic

climate change and immune health.

Extreme Heat Events

One of the most well documented consequences of climate change is the increased

frequency of extreme heat events and their effect on the environment and consequently, human

health. Skilton (2018) explained that extreme heat events have largely been rare. As a result of

this rarity, humans have not experienced enough extreme heat events to develop some form of

resilience in response. Skilton (2018) highlights that even the slightest increase in mean

temperature can have drastic effects on the frequency of extreme heat events. Research from

Rocklöv and Dubrow (2020) found similar results, whereby the increase in the average global

temperature by one-degree has resulted in increased sea level and average warmer temperatures

globally. Skilton (2018) explains that extreme heat events can change both in frequency and

duration. Where an event was once four days long, it now lasts eleven days for example.

Increasing temperature and more frequent extreme heat events are contributing to more frequent

and intense wildfires. In 2020, California experienced some of the deadliest and most destructive

wildfires on record. According to an article circulated in the Los Angeles Times, the amount of

acres burned in California wildfires has been steadily increasing. In 2012, the Rush fire burned

approximately 272,000 acres in comparison to the August Complex fire that burned around

746,000 acres. The effects of climate change on the wildfire season in California are complex

and vary (Williams et al., 2019). Additionally, it is well documented that increased warming has
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an effect on wildfire throughout the western United States, specifically in forested regions

(Williams et al., 2019). This is as a result of intensifying atmospheric moisture demand and

reduction in summer soil moisture as the snowpack declines (Abatzoglou & Williams, 2016).

Consequentially, Williams et al. (2019) demonstrated that the effects of anthropogenic climate

change on wildfires in California have arisen, somewhat alarmingly, from a small amount of

warming. Warming trends are expected to increase as meaningful change has yet to be

implemented to combat warming, and these effects will be felt at an even greater level compared

to today.

Summary

For a great portion of history, human life expectancy was low as was population growth,

but advances in health, agriculture, and technology have allowed the human population to grow

rapidly. This growth has been costly to the environment as the march toward progress has

incurred damaging effects. Climate change poses an existential threat to the entire planet and it is

crucial that action is taken to mitigate the damage that has been done. In the final analysis,

Climate change threatens the health of the public in many ways. One of the most damaging ways

that climate change affects public health is the impact it has on vector-borne diseases. Vector-

borne diseases are capable of transmitting deadly diseases and are responsible for around 17% of

infectious illnesses. As the temperature increases due to climate change, the effects of vector-

borne diseases are only going to get worse. Increasing warming trends are shifting the trajectory

of some of the most harmful disease vectors. Harvell et al. (2002) found that warmer

temperatures have resulted in a wider distribution of diseases such as Lyme disease, malaria,

plague, and dengue. Harvell et al. (2002) found that most of the previously mentioned diseases

spread into areas of higher latitude, directly following habitat amplification of ticks and
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mosquitoes. Climate change is also having increasingly extreme effects on human health.

Research exceedingly demonstrates that at a neurological level, humans and animals are

increasingly susceptible to the effects of climate change. Research (Pallotta et al. 2017) has

demonstrated that temperature can affect the organization of the brain and alter gene expression.

Finally, the effects of climate change on our immune system are potentially detrimental. As

explored in Ray and Ming (2020), climate change has the ability to disrupt normal immune

functioning. Increased warming and carbon dioxide in the environment has resulted in longer and

more intense pollen seasons, putting those with asthma and severe allergies at risk. As warming

trends continue to disrupt the natural environment, it is hypothesized that immune responses may

become more erratic in response to novel organisms. Beyond individual health concerns,

anthropogenic climate change is causing more frequent extreme heat events. These heat events

are detrimental on global human health and the environment. The increased warming has

increasingly severe effects on wildfires, as shown in California over the past five years. Each

subsequent fire season in California has gotten worse and burned more acreage than previous

years and these events are expected to get worse. In closing, climate change is an existential

threat that all of humanity faces, and a global response is necessary in order to facilitate

meaningful change before the consequences worsen.

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