Pre-Anthropogenic Carbon Levels and the Carbon Cycle
Carbon and its movement through the different systems on Earth plays a role in the regulation of climate. Carbon can be locked in a few different forms. There are sources of organic carbon, found in molecules like sugar, cellulose, and other biological molecules. Many of these molecules can be found bound up in living plants and animals and act as energy storage or structural components.
Some of this carbon may move into a long term storage reservoir. One example is carbon that is converted over time and pressure into coal and fossil fuels. This carbon is often located underground in sub terrestrial deposits. Another example of long term carbon reservoirs include deep ocean waters. Organisms that are in upper pelagic or mesopelagic waters die and sink down into deeper ocean areas. It can take several hundreds of years for upwelling to return deep ocean deposits of carbon back to surface waters.
Much of this organic carbon is eventually decomposed and may be converted into inorganic carbon, like those found in carbon dioxide gases or other forms of dissolved inorganic carbon. Carbon dioxide and other greenhouse gases are essential components to the atmosphere. Without them, solar radiation would not be reflected back to earth, resulting in a much cooler planet unable to sustain the biodiversity we see today. Greenhouse gases play an important role in the earth system. They act as an insulation layer to reflect radiation back to earth, trapping radiation and helping to keep the planet warm. A healthy amount of CO2 in the atmosphere is vital for keeping atmosphere, lithosphere and hydrosphere temperatures stable.
One of the major misconceptions that will need to be addressed while teaching this unit is the idea of weather versus climate. Weather is the day to day conditions in an area. This includes short-term precipitation events and temperature. Weather can change day by day or even hour by hour in certain areas. For example, in Connecticut, the weather for a single week during June can vary wildly. It may be in the 90s and sunny one day with the next day weather in the 60s and rainy.
Weather certainly can play a role in some of the cases that are presented in this study. For example, a sudden cold snap may kill tender ragweed plants that have started to come up. This may have a temporary impact on allergies as a major contributor of pollen is removed. However, this may be the exception and not the rule in this area, and pollen counts could return to normal the next season.
Climate, on the other hand, is the long term weather conditions that are typical for that particular region. Climate is long-term and gives the average conditions for the region including seasonal temperatures and precipitation. Climate is impacted by more than just carbon. The angle of the sun’s radiant energy and the rotation of the earth’s orbit have impacts on the air and water currents due to convection as areas of land and water heat up. The patterns of precipitation and temperature contribute to the average climate of a region.
A driving force behind this unit is understanding the changes in climate and how they can have an impact on human health. The planet is a complex system and there are multiple factors that can and do influence climate cycles. When changes in these cycles occur, there is a response by these systems to help return back to normal. We would consider this to be a negative feedback loop. In negative feedback loops, there is a stabilizing effect where the response essentially shuts off or stops the stimulus allowing for a return to normal levels. In a way, this system works similarly to the feedback loops in the human body, allowing for maintenance of homeostasis.
Sometimes, changes in a system can cause a disruption, which can result in abnormalities. In some cases these changes may even move a normal system into a positive or amplification feedback loop. In these cases, the stimuli continues to increase, causing a greater increase in the output. This cycle is perpetual, continuing to move the systems away from the average.
Another common misconception that will likely need to be addressed in class is the idea of periodic ‘thawing’ and ‘freezing’ that the earth seems to go through. There are times in the Earth’s past where CO2 levels have increased and decreased as part of these natural feedback loop cycles. This is true—studies of CO2 from ice cores have given us a picture of the atmosphere saturation at points hundreds of years ago. However, the levels of CO2 in this ancient ice demonstrate that, while CO2 levels do naturally vary and are tied with the heating and cooling systems on Earth, it never rose above 300ppm.1
Historic carbon dioxide, back as far as 800,000 years, had concentrations averaging under 280ppm. In fact, over the last 800,000 years, the highest the concentration of CO2 was 300ppm.[1] However, since the industrial revolution, the concentration of CO2 has grown unchecked, increasing by over 100ppm in only a couple of centuries well past the previous high threshold to levels near 410ppm.
This extraordinarily fast increase in carbon dioxide is linked in part to an increase in combustion of fossil fuels which remove stored organic carbon and changes it into inorganic gas through combustion. In addition, logging, land clearing, and burning add additional carbon dioxide. In total, net carbon emissions increased by 51% between 1990 and 2015 due in part to the increasing demands for energy production and land use changes on a global scale.2 All of these are considered anthropogenic contributors of carbon and other greenhouse gases, increasing levels at a rate previously unseen. These anthropogenic impacts tip the scales, dumping additional carbon gases into the atmosphere in a way that the negative feedback loops are unable to mitigate.
While much of the focus thus far has been on carbon, it is important to note that other greenhouse gases are also experiencing similar increases in emissions. Some of these greenhouse gases are even more potent than carbon dioxide. For example, methane is responsible for about 20% of the global warming seen to date and has a global warming potential of 30 times that of carbon.3 Nitrous oxide, another greenhouse gas, is even more potent than methane. All of these factor into the global warming that has happened and is projected to continue into the future.
Warming Trends and the Impact on Zoonotic Vector Ranges
Indicators of Climate Change
Climate change can have long term impacts on large regions. In many areas, the average temperature has increased and is predicted to continue to increase as anthropogenic carbon continues to be emitted in the atmosphere. The United States has seen an average increase of 0.16oF per decade since 1901. This increase has almost doubled per decade since the late 1970s, falling between a 0.31 and a 0.54oF increase. Two of the hottest years on record have happened within the last 10 years.4 Warmer averaged temperatures have been seen globally with 2011-2020 being noted as the warmest decade on record. However, warming is not equally distributed. There are areas in the United States, such as the northern and western most states, that have seen larger increases in their average temperature while the southeast seems to have more limited increases.4
This increase in average temperature has many long lasting effects for seasonal weather patterns. Winters in the United States have had average temperature increases of almost 3oF since the late 1890s.4 Spring, summer and fall have also seen average temperature increases by between 1.4 to 2oF in this time period as well.
As climates change, the possibility for expanded ranges of vectors and the diseases they carry expand as well. Changes in climate can impact regions by opening up conditions that are suitable for novel arthropod vectors and reservoir species to colonize the area. This will, in turn, introduce new pathogens into these regions impacting the health of local populations. Many of the vectors of concern are arthropods and rely heavily on favorable climatic conditions to be able to sustain their populations. Climate changes to regions have opened up previously inaccessible regions by producing milder temperatures, increased humidity or rainfall, and conditions suitable for vertebrate hosts.
It is important to note that there is a lag between any changes to climate and the establishment of novel vector and host populations and that many of the cases presented here-in may have other mitigating factors such as global transport and accidental introduction to areas. However, climate change works in synergy with these incidents. While introductions to new zones are important for expanding range they would never be able to establish in these areas without suitable climates. There are several pathogens that are of particular medical concern in the United States that have seen expanded ranges due to changes in climate opening up habitable areas.
Example 1: Ixodes scapularis and Lyme Disease
Lyme disease is caused by a spirochete bacterium Borrelia burgdorferi and is transmitted by the deer tick Ixodes scapularis. These ticks often use deer and other common field and woodland organisms as hosts. However, the main host of interest is the white footed mouse which acts as a natural reservoir for Borrelia. Ticks that feed on these mice are able to pick up and transmit the bacteria through their bite.
Lyme disease itself is considered to be one of the most common vector borne diseases in the United States with approximately 30,000 confirmed cases reported to the CDC each year.5 These numbers are considered to be severely underreported since additional survey methods by the CDC and other public health boards have models predicting over 400,000 annual cases.5 Lyme disease often presents with erythema migrans, or a bull’s eye rash that appears between 3 days up to a month post infection. The rash itself can grow up to 12 inches in diameter and may feel warm to the touch but is otherwise painless. Additional symptoms can appear later on post infection and include arthritis in joints, Lyme carditis, meningitis, and facial palsy. These symptoms range in severity by patient and can be short term when treated early or persist for years post infection.6
There is evidence that the range of the tick has expanded. One study looked at the appearance and establishment of the tick in ranges of Canada that were previously unable to sustain them due to the temperature.7 Furthermore, shorter winters expand tick activity and can lead to an increase in breeding and active biting in areas where temperatures are milder. This is only exasperated in areas where human activity also increases due to milder temperatures. Milder winters, earlier springs, and prolonged warmth into fall can lead to increased outdoor activity, increasing exposure to ticks and increasing incidents of infection.
Since the mid-1990s, cases of infection have doubled per 100,000 people in the northeastern part of the United States with some of the largest increases happening in Maine, New Hampshire, and Vermont— states that had low reports of infection only 20 years prior.7 It is no coincidence that much of the northeast has also experienced changes in their climate with regards to both temperature and humidity. Since the 1960s, there has been an average increase of temperature of 2oF with projections of up to an additional 10oF by 2080 of anthropogenic carbon emissions continue unmitigated.8 This projected increase is followed by a projected rate of encounter and infection.
One effect of these seasonal increases is milder winters in some regions or lengthening the growing season by supporting earlier spring thaw and later hard frosts in winter. These changes can have large impacts on the suitability of regions to sustain arthropod vectors, causing shifts in their populations to expand into previously un-colonized areas.
Not only do warmer temperatures lead to a more sustainable zone of habitation for the tick, but the warmer temperatures can also lead to expanded ranges for reservoir vectors. White-footed mice populations have also moved into previously unestablished areas here previously long winters prevented populations from thriving.9 Milder winters and earlier springs also provide an increased bounty of resources to sustain larger mouse populations and larger nests in areas where resources were historically limited.
Interestingly, while the population of Lyme carrying ticks has increased, infection rates appear to have declined in Connecticut from about 4000 diagnosed cases in 2008 to around 1900 cases in 2018.10 This steadily decreasing trend is likely due to the robust public awareness and education programs maintained in the state of Connecticut to educate citizens on prevention of tick bites.10
While I. scapularis is primarily associated with Lyme disease, it is also a vector for several other diseases of concern including ehrlichiosis, anaplasmosis, babesia, and the Powassan virus. A breakdown of these diseases with their symptoms and treatments are located in a reference table at the end of this document.
Example 2: Amblyomma americanum and Southern Tick Associated Rash Illness (STARI)
The deer tick isn’t the only tick species to see an expanded range. The lone star or turkey tick, Amblyomma americanum, is susceptible to cold temperatures and previously inhabited areas of the southeast United States but has recently moved along the coast up to and beyond upstate New York. Temperatures play a limiting factor in the expansion of the range as the tick requires a specific range to encourage egg development and activity.11 While it may be able to survive in colder temperatures, reproduction is severely diminished preventing establishment in areas where temperatures dip below and sustain at freezing for extended lengths of time.11 Just as in the case of the deer tick, A. americanum range has benefited from the warming trend seen in the Northeast region and is able to move into and colonize previously inaccessible regions.
The lone start tick is responsible for several medical conditions of interest including Southern tick associated rash illness which is similar in appearance to the erythema migrans rash seen in Lyme disease. Other pathogens transmitted by the lone star tick include the Bourbon virus, Heartland virus, and Francisella tularensis which causes tularemia. One of the most interesting outcomes of the lone star tick bite is a development of alpha-gal syndrome which is characterized by an allergic reaction to red meat and mammal products.
Example 3: Gulf Coast tick and Rickettsia
The Gulf Coast tick is another arthropod vector that has seen an expanded range. In a Connecticut Agricultural Experiment station newsletter, the movement of the tick is discussed. Normally endemic to areas of the Gulf Coast and Mexico, this tick has seen expanded ranges traveling up the eastern seaboard into the northeast.12 This tick was first reported in Fairfield County in August 2020 and has likely established a population.
One of the medical conditions linked to this vector is rickettsia, a spotted fever, which is able to infect both humans and canines. Like the lone star tick, increasing temperatures in the northern latitudes have provided an expansion of suitable habitats for the tick to both live and reproduce in. As temperatures continue to rise it is highly likely that contact with these vectors will increase as will incidence rates of infection with the pathogens they carry.
Example 4: Mosquitoes
Ticks aren’t the only vector to enjoy expanded ranges due to climate change. Mosquitoes, like other arthropods, rely heavily on external conditions like precipitation and temperature to support the development of areas that are suitable for habitation. Of the 3500 known species of mosquitoes over 2600 of them are native to the tropics and subtropics as they prefer humidity and increased temperatures.13 14 There are mosquitoes that are also found in cooler regions—including one species that lives in the Arctic tundra and undergoes a large hatch in the summer as the heat melts the snow cover that is over the permafrost in this region.
Like the tick, mosquitoes are arthropods that feed on vertebrate blood. Female mosquitoes will seek out a blood meal in order to provide the protein essential for the healthy development of their eggs and larvae. Mosquitoes need a water source in order to lay their eggs, as their larvae are aquatic. This water source will provide a place for their larvae to develop into the flying adult. Their reliance on water means that mosquitoes tend to favor areas that are humid with adequate precipitation and relatively warm temperatures.
As climates change and areas further north experience increases in temperatures and humidity, they become more tolerable for mosquito populations. One study conducted found that only 5% of the Northeast is currently habitable by the Asian tiger mosquito (Aedes albopictus) which is known to carry several infectious diseases. However, projects estimate that this habitable area will increase to 16% in 2035.13
Mosquito ‘season’ is also changing. Mosquitoes are being encountered early in the year and persisting later. On average, mosquito seasons have increased by almost a month in most major US cities. Hartford has seen a gain of 37 days since the 1980s.13 As with ticks, increases in season length can increase encounters and have an impact on the number of cases of mosquito carried diseases are present in a population.
Currently there are 49 species of mosquitoes in Connecticut, 28 of which are considered to be important disease vectors.14 Of these mosquito species 10 of them have shown an increase in population size between 2000 and 2019.10 There are several different viruses or parasites that can be transmitted by mosquito bites including Eastern equine encephalitis and West Nile virus.
Two of the mosquito species of concern in Connecticut are Aedes aegypti, a primarily subtropical species, and Aedes albopictus which was first identified in 2006 and is now showing increases in populations in New Haven and Fairfield counties.10 This mosquito is a known worldwide carrier of several diseases including Cache Valley virus, West Nile virus, dengue, chikungunya, and Zika virus. Currently, the individuals caught in Connecticut have only carried Cache Valley and West Nile but there is always a concern of the introduction of new viruses now that the vector is currently in the area.10 It is likely that A. albopictus is at its northernmost range currently but if temperatures continue to increase through climate change it is possible that the range can expand further into states like New Hampshire, Vermont, and the southern border of Maine.15
Expanded ranges of vector arthropods are not the only possible concern. As climates change, there are selective pressures applied to their natural predators as well. A recent study found that dragonflies, a predator of mosquito larvae, are experiencing an unexpected population shift due to climate change. Dragonflies that have reduced pigmentation in their wings and bodies are better able to deal with the increased temperatures associated with climate change. However, this change in coloration impacts the male dragonflies’ ability to attract mates, decreasing reproductive success.16 A reduction in dragonfly populations can lead to a boom in mosquito populations and a corresponding increase in mosquito transmitted diseases.
Warming Impacts on Free-living Aquatic Pathogen Range
Indicators of Climate Change
There are additional consequences to increasing temperatures including warming of surface and shallow fresh and ocean waters. A study published in 2015 found that water temperatures of streams in the Chesapeake Bay area had an overall average increase in the surface temperature of the water of 1.2oF in at least 79% of the sampled sites since the 1960s.17 18 Surface temperatures of lakes have also increased between 1-2oF since 1985, especially in Northern latitudes such as the Great Lakes. 19 20
Oceans are experiencing similar trends to inland freshwaters. Surface sea temperatures (SST) have increased at a rate of 0.14oF per decade since 1901 and have been higher during the past three decades than any point in past records.21 This trend isn’t universal—the warmest areas tend to be near the equator and some areas, such as in the North Atlantic actually saw a temperature decrease although this is probably due in large to the melting of previously frozen polar ice cooling the waters.22 Changes in the surface sea temperature can have a large impact on wind and weather patterns, influencing the frequency and intensity of storms.
Below surface waters, warming is also present. The epipelagic and upper-mesopelagic zones of the ocean (down to nearly 700 meters) act as heat sinks for the extra heat generated by global warming and have also increased in temperature. The ocean is able to absorb a great deal of heat energy without a correspondingly large change in temperature due to water’s high heat capacity, helping to maintain atmospheric temperatures. However, steady increases in anthropogenic greenhouse gases continue to push the ocean heat content, showing an increase in nearly 18x1023 joules since the 1990s.23
Vector-borne diseases are not the only infectious agents that can benefit from a change in climate. Warmer ambient temperatures may also mean warmer waters—and the expansion of water-borne illnesses. While water itself is an excellent heat-sink for atmospheric heat, surface and shallow waters are impacted by increased temperatures and expanded warming seasons. As a result, certain water-borne pathogens or pathogens that are rarely seen outside of subtropical or tropical regions are moving into what is considered to be cooler waters. These outbreaks can be amplified by increases in extreme precipitation events.
Example 1: Ciguatera Fish Poisoning
One example of this is the increased range of ciguatera fish poisoning (CFP) from the Caribbean into areas of the Northern Gulf of Mexico.24 Ciguatera often occurs in large reef fish like king mackerel, yellowfin grouper, barracuda, and several snapper species. There is a bioaccumulation of the ciguatera-toxin produced by the marine dinoflagellate Gambierdiscus toxicus which acts a food source for many of the prey species that these predatory fish feed upon. While this toxin is harmless to fish species, it is dangerous in humans and can cause symptoms from nauseas and vomiting to cardiovascular and nervous symptoms including abnormal heart rhythms (bradycardia or tachycardia), ataxia, and even cold allodynia neuropathic pain.25
A study completed in 2014 looked at the relationship between CFP cases in the United States, strength of tropical storm events, and surface sea temperatures. This relationship is due to the nature of G. toxicus to favor damaged or bleached reef formations and warmer waters. Intense tropical storms can cause widespread reef damage, especially in shallow water reefs like those found in the Caribbean.24 Combined with increased surface sea temperatures (those remaining above 24oC) these areas create the perfect breeding grounds for G. toxicus and abundant grazing for herbivorous fish species. Climate changes and global warming events have played a role in all aspects G. toxicus range as they can increase storm intensity and frequency, increase the temperature of surface waters, and cause coral bleaching providing the perfect habitat for increased habitation.24
An increase of even one storm per month lead to an 11% increase in CFP cases and there are predictions of increased storm frequencies and severity in the North Atlantic.24 The model constructed by this study also noted that a surface sea temperature increase of 1oC during high bloom months like August resulted in a 62% increase in CFP cases.24 It is likely, according to their model that moderate increases in both surface sea temperature and storm frequency could increase cases could grow by as much as 200-400% yearly.24
While cases of CFP are rarely fatal, an increase in the number of cases is concerning especially since symptoms can persist from as few as two days up to long-haul cases where patients take more than a month to recover.
Example 2: Naegleria fowleri and PAM
There are also several freshwater examples of expanded pathogen range due to changes in climate. Naegleria fowleri is an ameboflagellate, known colloquially as the “brain eating amoeba”. It is a naturally occurring species that prefers freshwater hot springs and warm lakes and rivers and can be found on virtually every continent. It is thermophilic and will grow best in waters that reach 46oC.26 In cooler temperatures, it is often found in the sediment of rivers and lakes where it remains relatively not pathogenic.
Infections of N. fowleri are most commonly associated with the southern United States during summer months when water temperatures increase and encourage the amoeba to enter into the trophozoite phase.27 This parasite enters through the nasal cavity of those swimming in warmer waters and penetrates through the cribriform plate into the brain causing fulminate (rapid) brain degeneration.27
Symptoms of primary amoebic meningoencephalitis (PAM) caused by an N. fowleri infection in early stages are very similar to those of bacterial meningitis. They can include nausea, vomiting, headaches, stiff neck, and photophobia. These symptoms usually occur between around five days after the amoeba has burrowed through the cribriform plate.27 The patient then begins to rapidly degenerate and may experience a loss of balance, seizures, and coma. Death typically occurs within a week to a week and a half after infection due to intracranial edema and destruction of brain tissues. Of the 143 known cases of PAM, only 4 people have survived.26 27
Cases of N. fowleri infection make the news because of the rareness of infection and the high mortality of those infected. Recently, some of those cases have been in northern areas where cases are not traditionally expected, including 1 case in Indiana, and two cases in Minnesota.26. In 2010, a case of infection was confirmed in Minnesota, making it the northernmost infection in the United States. Officials cite a hot summer and increased water temperatures for the case, activating dormant N. fowleri found in the sediments of those water bodies.28
As climates change and average temperatures rise, there may be a corresponding rise in the temperatures of surface waters. An article published by NASA in 2015 found that freshwater lakes are warming an average of 0.61 degrees each decade.29 Some of the largest increases were seen in northern latitudes, such as in Minnesota. Furthermore, milder winters and expanded warm seasons can increase exposure risk by encouraging extended periods of swimming and water sports. As populations aim to keep cool, participation in these outdoor events may increase incidents overall, not just in the north, as more people participate in risk behaviors that may expose them to the amoeba.
Allergies and the Expanded Growing Season
Indicators of Climate Change and Ragweed Seasons
Seasonal allergies due to pollen are also impacted by these changes both in their duration and their severity. Many people suffer from immune responses from the pollen that is released from plants in bloom, including ragweed and grasses. Pollen is released as part of the reproductive cycle of plants and is used as a dispersal mechanism. Since pollen is carried by the wind it can be distributed widely across a region.
As people breathe in the pollen or touch surfaces where it has stuck and rub their eyes or mucosa they take in these pollen grains. Pollen has proteins that coat the surface and act as antigens. Part of the immune response is to recognize foreign antigens, or non-self, and trigger a series of reactions aimed at defending the body against perceived threats. Often these threats are infectious pathogens, but there are cases where the body will also respond to non-pathogenic proteins.
Seasonal allergies such as those to grass pollen and ragweed are an overreaction of the body to these pollen granules. Symptoms of pollen allergies can be mild to moderate. One common symptom is allergic rhinitis, which is linked to congestion and sneezing or general irritation of the nasal tissues. Allergic rhinitis is relatively common, especially in areas that experience high pollen counts during the spring, summer, and fall. In addition to these mild respiratory symptoms, more concerning increases in asthma related respiratory distress also increase due to sensitivities to respiratory tract irritation.
In many states, growing seasons have increased on average by two weeks since the early 20th century with the steadiest increase happening since the 1980s.30 This change in the growing season length can be linked to data showing that the last hard frost in spring is occurring on average six days earlier than the 1980s and the first killing frost of autumn occurring almost 7 days later than average.30 In Connecticut specifically, frost days have decreased since the 1920s in a large portion of the state, altering the growing season by allowing for increased grow times and milder winters.10 While this is amazing news for farmers and hobby gardeners, with longer growing seasons, early bloom date, and later frosts, this can expand the pollen bloom seasons linked to allergies.
In a 1995 ragweed pollen study conducted by the National Allergy Bureau across 11 locations in Canada and the United States, 10 of the cities had an increase in the allergy season—with some locations having an overall gain of over 20 days in length.31 Warmer temperatures early in spring and increased available carbon dioxide concentrations allow for an increase in pollen production and higher overall pollen counts.32 Furthermore, ragweed usually matures in late summer to early fall but will continue to be fruitful until the first hard frost. Expanded growing seasons allow for ragweed to bloom earlier and continue blooming longer, resulting in longer allergy seasons across these regions.33
Heat Related Illnesses and Deaths
Indicators of Climate Change
Heat waves, periods of at least three days where highs were sustained 90oF or more, are also occurring at a greater frequency, duration, and intensity. On average, there are around 6 heat waves per year, up from two in the 1960s, and those heat waves last at least a day longer.34 One study found that 46 out of 50 cities not only saw an increase in the frequency of heat waves but also an increase in the intensity.34
Urban areas are susceptible to heat waves because of the infrastructure of the city itself. Increased amounts of asphalt and reflective surfaces like metal help to trap and re-emit heat which increases the ambient air temperature. In addition, heat is generated by running vehicles, buildings, and the large population in the area. This creates a ‘heat island effect’ increasing the overall temperature in these urban areas. In areas that are low-income and may have homes that lack insulation or air conditioning, this increased heat is compounded putting populations in this area at higher risk of experiencing heat-related complications.10
In Connecticut specifically, the average temperature has increased by about 3oF from 1895 to 2019 state wide even though the number of significant heat days has not increased significantly.10 One of the most dangerous observations has been an increase in warmer nighttime temperatures which prevent cooling and have negative long term health consequences especially in high heat days, leading to the increase in medical emergency cases.
Heatstroke and Heat-Related Illnesses
As previously mentioned, the number of extreme heat days (those with temperatures above 90oF) have not statistically increased in Connecticut as of yet but as average temperatures increase it is expected that this trend will increase in the future. If changes are not made, it is possible that the number of days could increase from around 3 per year to around 44 per year by 2050.10 In spite of this lack of visible increase, there has still been an impact on human health.
In Connecticut, hospital visits averaged around 422 visits and 45 hospitalizations per year between 2007 and 2016 due to heat related conditions although it is expected that these numbers are under reported because symptoms are often attributed to other conditions.10
Heat related deaths are those that are directly related to exposure as the underlying cause or as a contributing factor. Heat exhaustion and heat stroke occur due to prolonged exposure to high temperatures or due to physical exertion in high temperatures. Heatstroke is especially dangerous as the body temperature spikes and can rapidly impact the cardiovascular, respiratory and nervous systems of patients. Heatstroke can come on quickly and is aggravated due to high temperatures, high exertion, and dehydration. This is part of the reason behind the increase in football training camp deaths in August months—student athletes are in the perfect storm of conditions for heatstroke.35
Part of why extreme heat is so harmful is that it impacts the body’s ability to maintain a safe temperature. The body has systems in place that are able to help regulate internal temperature, including sweating, however high heat days can lead to increased dehydration and other conditions that increase susceptibility to heat stroke. Warmer summer nights increase the inability of the body to cool itself leading to more cases.10 34
The extreme heat can also aggravate other heat-related complications, especially in the elderly or those with chronic-conditions since all body systems are impacted. Those patients with kidney, lung, or heart diseases are at risk because of the impact on those organs but it is also dangerous in populations that have diabetes. Groups that are at risk include the homeless, populations over 65, and individuals who are spending a significant amount of time outside doing physically demanding tasks. Inadequate temperature control measures or ventilation also puts indoor workers or individuals at risk as well.
Implications of further climate change on ice and glaciers
Indicators of Climate Change
Glaciers are losing mass as temperatures increase. Between 1956 and 2019, there has been a cumulative loss of nearly 30% of glacier mass globally.36 Glaciers found in Alaska and Washington have seen corresponding losses in mass between 20 to 40% since the 1980s.37 Another site, Glacier National Park located in Montana has 37 glaciers, which have all lost mass. An aerial survey of the park conducted to capture glacier recession during 1966 to 2015 by the US Geological Society estimates over 34% loss of the overall mass for the site.38
Permafrost, like glaciers, have also started to thaw due to warming temperatures. Permafrost is a layer of ground that is in a hard-frozen state found mostly in the northernmost latitudes near the Arctic. There are several areas that are extensively composed of permafrost layers—Alaska is about 85% permafrost.39 One of the ways that permafrost temperatures are measured is by drilling boreholes into the land and sampling at different depths. A data set published in 2020 by the University of Alaska Fairbanks found that 13 of the 14 borehole sites in Alaska have increased in temperature at both 49 and 85 foot depths.39 This warming allows for several things to occur—not only does it release frozen biomass in these areas which can have implications for human health, but it releases trapped greenhouse gases like methane and carbon dioxide into the atmosphere.40
Example 1. Unlocking the Viral Vault
Glaciers can act as time capsules for many things, including viruses and biological materials. Ice, especially ice that is deeper in the glacier, can be several hundreds of thousands of years old. Small pockets of ice may host bacterial, viral, and fungal pathogens from the environment or from frozen biological samples.
As climate change causes the recession of glacial ice, there is the potential for viruses to be released. Some cores of glacial ice from a Tibetan glacier had 28 novel virus genera that are calculated to be over 10,000 years old.41 There are concerns that some of these viruses may be influenza virus, the human calicivirus (HuCV), or other strains that might re-emerge.
Example 2. Thawing Permafrost and Anthrax
Illnesses thawing from the ice to infect humans is not just theory. In the Yamel Peninsula, there were cases of increasingly warm periods causing extensive melting of the active layer and some of the frozen soil underneath. In these deeper, more permanently frozen soils there may been organic material including bodies of animals or people who died due to different pathogenic outbreaks. In this particular area of Siberia, one case in 2016 involved the thawing of a reindeer carcass that was infected with and died from anthrax.43 44
Anthrax infections are caused by a soil bacteria called Bacillus anthracis. Anthrax is a soil bacterium that, as part of its life cycle, can release infectious spores. These spores can be inhaled, ingested, or introduced into the body through open cuts. When the spores enter human or animal tissues they become active and produce toxins that can be lethal. When a grazing animal eats grass that is infected with these spores they begin to multiply and spread.
The toxins produced by anthrax can impact the body in a variety of ways depending on the route of introduction. For example, cutaneous anthrax infections are the least dangerous and often result in cutaneous ulcers and blisters.42 Unaddressed cutaneous infections are dangerous and can result in loss of a limb due to extensive tissue damage or, if left unchecked, death. Inhalation or ingestion are more severe. With inhalation related anthrax cases, the anthrax can infest lymph nodes of the chest and alveoli, causing breathing problems and eventual organ failure. These cases are fatal in the untreated and have a 55% survival rate in those who receive prompt medical care.42 Ingested anthrax is also survivable with treatment and exhibits symptoms similar to those of inhaled anthrax.
As the active layer and the layer of permafrost that covered the carcass thawed, the bacteria were able to thaw as well and the bacteria were able to make their way out into the soil. Grazing reindeer consumed the pathogen. As herders tended to these animals and came into contact with infected animals or spores themselves, they became infected. This outbreak ended up killing one person and hospitalizing multiple others. It also resulted in the death of over 2000 reindeer. 43 44
If warming trends continue, it is likely that out breaks like this may occur more frequently in the future. An NPR article cites that across northern Russia there are around 7000 burial grounds that are covered by thin layers of permafrost similar to the one for the infected reindeer.44 It isn’t out of the realm of possibility that other viruses or bacteria may be frozen in the ice.