Climate Impacts: Field of Action Human Health

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Human health can be affected by climate change.
Source: Miss X/

Humans react sensitively to extreme weather events. Heat is a direct burden on human health and can lead to severe diseases of the cardiovascular system and, in extreme cases, to death. In addition, climate change favours allergies and pathogens or their vectors. Sunny years increase the risk of UV-related health damage.

Table of Contents


Heat stress

Extreme heat events can have a direct impact on human health, and their effect depends crucially on their frequency, intensity and duration. In addition, the body's ability to adapt can be impaired by pre-existing conditions (e.g. diabetes) and consumption of medications and stimulants. The human cardiovascular system in particular is severely stressed by extremely high temperatures and, in extreme cases, can lead to death.

Older people are particularly affected by heat stress, as the adaptation process for thermoregulation of body temperature slows down with advancing age and the ability to release physical heat decreases. With demographic change and an ageing society, the risk potential in the population is therefore increasing.

Stress, mental disorders, anxiety or depression can occur as further health burdens. Heat stress reduces physical performance and thus also has a negative impact on social productivity in industry and commerce.

Heat stress will increase. This is not only due to the increasing number of heat periods per year and their longer duration. The densification of inner cities and the increasing concentration of the population in growing conurbations also contribute to this. The densification of inner cities will further increase the heat island effect, while the growth of cities into the surrounding countryside will increase the area of heat islands.

Indicator from the Monitoring on the DAS: Heat exposure and Public awareness, Heat-related mortalities


Allergic reactions due to pollen

Allergies are increased reactions of the immune system to certain foreign substances (allergens). They are the most common chronic diseases in Germany and thus a relevant public health issue. The most common triggers of allergies in Germany are pollen from early-blossoming trees such as hazel, alder and birch, as well as from grasses and herbs. They can trigger respiratory diseases such as hay fever and asthma. The associated physical impairments reduce the quality of life of those affected and lead to reduced performance.

As a result of a climate change-induced increase in average air temperatures, the flowering period of certain plants (e.g. hazel, alder) and thus the pollen season now begin much earlier than in the past 20 to 30 years. Phenological observations have shown that the start of hazel and alder flowering was up to 26 days earlier between 1961 and 2017; the start of flowering of birch and grasses was also shifted forward by an average of one to one and a half weeks between 1991 and 2017. For grasses and herbs in particular, a lengthening of the pollen season is also observed in the course of climate change. Accordingly, the period of suffering for people with pollen allergies is lengthening. In some years, one pollen season already goes directly into the next, i.e. the probability of a continuous pollen count over the entire year increases with climate change. Pollen allergy sufferers will thus miss the allergy-free break.

It is also expected that plants will release more and more potent allergenic pollen in the future with an increase in carbon dioxide concentration in the air and higher air temperatures. In addition to this changing "pollen load" the pollen spectrum is also changing with climate change and shifting vegetation zones. As air temperatures rise, plants that were previously not native to Germany, some of which have a very high allergic potential, migrate and spread rapidly, such as the common ragweed (Ambrosia artemisiifolia). Ragweed blooms between August and the first frost. Each plant can release up to one billion flower pollen and this pollen is much more aggressive than the pollen of native plants. Even a concentration of more than ten pollen grains per cubic metre of air can trigger severe allergic reactions.

Indicator from the Monitoring on the DAS: Contamination with pollen of ragweed


Potentially harmful microorganisms and algae

Naturally occurring microorganisms and algae (protozoa, bacterial strains, algal or fungal species) in the environment can affect human health. Among the better known water-borne and potentially dangerous bacteria are cyanobacteria ("blue-green algae"). There are several thousand different species of "blue-green algae", but only some of them (in the Baltic Sea e.g. Aphanizomenon, Nodulariadia) produce toxins such as peptides and alkaloids. Since the quantities produced are only very small under normal circumstances, there is no danger to humans. However, there is a health hazard if the toxins are present in the water in higher concentrations. The concentration of toxins in the water is very high during the "bloom".

The bloom of cyanobacteria is enhanced or made possible by favourable development conditions, such as a high sea surface temperature. Especially in nutrient-rich waters, they can proliferate en masse when temperatures are warm. A climate change-induced increase in water temperatures thus favours the emergence of an algae bloom.

At high concentrations, the toxins can cause skin irritations in humans and, if swallowed, nausea and vomiting. They also hinder breathing and are particularly dangerous for weakened persons. In some summers, this results in the closure of bathing waters.

In addition to cyanobacteria, species of the bacterial genus Vibrio, which occur naturally in brackish and seawater, also have an impact on human health. They can cause deadly infections, with the potential for infection depending on water temperature. As the oceans warm, the number of infections caused by vibrios could increase. In addition, the population as a whole is getting older and thus potentially more sensitive.

Indicator from the Monitoring on the DAS: Contamination of bathing waters with cyanobacteria – case study


UV-related health impacts

A direct health hazard is increased ultraviolet (UV) radiation, the most energetic part of optical radiation. It is not visible to humans. The sun is the natural source of UV radiation. Increased UV radiation has short-term (acute) and long-term (chronic) effects on the human body. Short-term effects include sunburn on the skin and conjunctivitis on the eye. Long-term effects include premature skin ageing, skin cancer and cataracts, a clouding of the lens in the eye. The rate of new skin cancer cases has been steadily increasing for decades in Germany and worldwide.

Climate change could exacerbate the situation because the number of hours of sunshine is increasing and cloud cover is decreasing. Analyses of the data of the UV monitoring network by the Federal Office for Radiation Protection (BfS) show that in years with a high sunshine duration, the daily sums of the sunburn-effective UV irradiance summed up over the year are also increased. This combined with the fact that the population spends more time and longer outdoors at higher temperatures, increases UV radiation exposure and raises the risk of skin cancer. Future development is uncertain so far, especially with regard to the future development of cloud cover.

Complex interactions between greenhouse gases, climate change and the stratospheric ozone layer can strongly influence a recovery of the ozone layer. The ozone layer is the layer in the stratosphere that more or less absorbs solar UV radiation. Low-ozone events have occurred more frequently in the northern hemisphere in the last two decades and can result in significantly increased UV exposure of the population.


Other climate impacts

Distribution and frequency of possible vectors: In Germany, mainly ticks and small mammals (e.g. rodents) play a role as disease vectors. Native mosquitoes can also transmit the West Nile virus. Shield ticks in particular could benefit from climate change. This would manifest itself, among other things, in an extension of their activity period or in the further spread and increase in frequency of previously less widespread tick species. Furthermore, the increasing spread of hitherto non-native vectors, such as the Asian tiger mosquito, could be relevant.

Indicator from the Monitoring on the DAS: Pathogen carriers – case study

Respiratory problems (due to air pollution): Climate change affects local pollutant concentrations and the resulting exposure of sensitive populations in many ways. The concentration of ground-level ozone in the air could increase. Exposure to air pollutants in inner cities could also increase further, partly due to the increasing number of hot days and the associated reduced air circulation. If winters become milder and the concentration of particulate matter increases in summer in inner cities, the annual peaks of exposure could shift from winter to summer.

Injuries and deaths due to extreme events: As the frequency and intensity of extreme weather events increase, so does the risk of people being injured or killed. Heat extremes cause a particularly high number of deaths.

Impact on the health system: Climate change could increase the number of cases of disease. Increasing and more intense extreme weather events could mean that health facilities are temporarily unable to fully perform their tasks because they are overloaded or the necessary infrastructure fails. Climate change requires investments in the health system, especially in education and training of employees, prevention campaigns, research and the reliability of infrastructures.