Trees, climate change and health: Part 1

 “The warming of the planet will be gradual, but the effects of extreme weather events (more storms, floods, droughts and heat waves) will be abrupt and acutely felt. Both trends can affect some of the most fundamental determinants of health: air, water, food, shelter and freedom from disease”. This is a statement made by the Director General of the World Health Organisation Dr Margaret Chan during UN led celebrations of the world environment day a couple of years ago. Her statement followed worldwide concerns about the impacts of climate change on the quality of life on the planet.

Coming across this statement only recently, I felt stirred to shed some light on her statement by explaining the relationship between climate change, human health and well being. In the same light, I was challenged put forward my thoughts on how an act as simple as planting a tree can go a long way to alleviate the effects of climate change on people’s health. Since climate change is attributable to unsustainable human exploitation of natural resources, my belief is that human action towards the restoration of the integrity of our natural environment can contribute significantly to alleviating the impact of climate change on human life. I will begin first by explaining the relationship between climate change and health.

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The environmental consequences of climate change, both those already observed and those that are anticipated, such as, changes in rainfall resulting in flooding and drought, heat waves, more intense cyclones and storms, and degraded air quality, affect human health and well being both directly and indirectly. Directly through impacts of thermal stress, and death/injury in floods and storms and indirectly through changes in the ranges of disease vectors (e.g. mosquitoes), water-borne pathogens, water quality, air quality, and food availability and quality.

Exposure to heat waves and death or injury from extreme weather is the more common direct impacts of climate change. Although we are in a part of the world (Tropics) where heat exposure is not a noteworthy challenge since we are used to raised temperatures, certain members of our community are less tolerant thereby putting them at risk from increased temperatures. The elderly and those who suffer from cardio-vascular and respiratory disease are less tolerant to high temperatures. This makes them likely to suffer more at the hands of climate change. Floods and cyclones can result in death or serious injuries to people as well. On the other hand, the trauma caused by these events on children may result in prolonged psychological damage. Mental health effects such as depression and anxiety may occur after these extreme events.

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Extreme weather events like cyclones, floods and drought also have far reaching indirect effects on people’s health and well being. They result in high temperature, water scarcity and water abundance which are all related to diarrhoeral diseases. After a cyclone or flood-event, rates of diarrhoeal disease, including cholera, may increase, especially in areas where sanitation facilities are poor. Heavy rainfall, even without flooding, may increase rates of diarrhoeal disease as latrines or sewage systems overflow. In Zimbabwe, high density residential areas such as Mbare, Chitungwiza and Tafara/Mabvuku are commonly affected. The cholera outbreak of 2009 bears testimony to this.

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Heavy rains lead to increased runoff which may result in the contamination of water sources. Perennial water shortages in Zimbabwe have led to many families making use of wells and other open water sources which are highly prone to contamination as a result of runoff. Water scarcity for personal hygiene and washing of food puts many Zimbabweans at high risk of diarrhoeal diseases and other illnesses related to poor hygiene.

The combination of high temperatures and rainfall resulting from climate change is likely to increase the spatial and temporal distribution of vector borne diseases such as malaria. After an intense rainfall event or a flood event, rates of vector borne diseases such as malaria can increase as mosquitoes breed in stagnant or slow moving pools of water. Viral and bacterial diseases may also increase because virus and bacteria replication rates are sensitive to temperature.

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High temperatures and water scarcity can put food harvests at risk while flood events can also destroy harvests. Low food yields may ultimately exacerbate undernutrition and lead to adverse health outcomes (especially physical and mental development of children). As rates of malnutrition increase, populations become more susceptible to other diseases. In Zimbabwe where HIV and AIDS is prevalent, poor nutrition coupled with HIV induced poor immunity levels put a large percentage of the population at risk of death.

Climate change affects temperature, humidity and wind which in turn affect the formation, transportation and dispersion of air pollutants. Climate change may therefore influence pollutant concentrations, which may affect health as air pollution is related to cardio-respiratory health. Exposure to high levels of ground-level ozone, for example, which is formed from the exhaust of transport vehicles, increases the risk of exacerbations of respiratory diseases such as asthma. Respiratory allergies and diseases may become more prevalent because of increased human exposure to pollen (due to altered growing seasons), molds (from extreme or more frequent precipitation), and dust (from droughts).

Addressing the effects of climate change on human health is especially challenging because both the surrounding environment and the decisions that people make influence health. However, given the aforementioned impacts of climate change on health, it is prudent to suggest that activities taken to ensure environmental sustainability and reduce greenhouse gas emission have several potential benefits for health as well.

One of the most gainful and holistic ways of tackling climate change while contributing to public health is through planting trees. While I am in no way suggesting that tree planting or good environmental stewardship can replace the provision of basic services such as primary health care, nutrition programmes, and adequate water supply and sanitation, I believe that completely ignoring the value of a healthy planet on human health and well being is potentially calamitous. I shall elaborate on the value of trees in the fight against climate change and the protection of human health and well being in the coming post.