Climate change impact on human health part1

Even if some politician on this world still ignore the fact of climate change, it takes place. Let us short recapitulate the effects.

Earth has several gases in its atmosphere that trap heat, including carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). These three gases, and others, retain heat and make the climate of the earth what it is, and the one in which all life that exists depends on for survival.

Many forces contribute to the Earth’s average overall temperature, including…

    Its orbit around the sun, which is more elliptical than circular.

    How hot the sun is – its temperature varies over time.

    How reflective the Earth’s surface is (white stuff, like ice caps, reflect light).

…but the temperature of our planet is most substantially influenced by the amount of greenhouse gas in the atmosphere.

When greenhouse gases trap heat, they raise the temperature of air, but also of water, and especially water in the oceans.

Where is global warming going?

Greenhouse gas make that we have higher temperatures and the air contains more water. This brings heavier snow and rain falls.

But carbon dioxide has other effects on our planet that may be just as important for our health as its effects on the climate.

About 30% of the carbon dioxide released into the atmosphere from human activities, such as burning fossil fuels, is absorbed into the world’s oceans. As it gets absorbed, it produces carbonic acid, which makes the world’s oceans more acidic.

Plants breathe in carbon dioxide and breathe out oxygen. When concentrations of carbon dioxide in the air rise, plants change in ways that have consequences for health.

The largest modifier of the health impacts of climate change is human behaviour, including the policies we create to protect health from climate change. It is important to understand the three main ways through which human action can reduce the effect of climate change on human beings:

–             Through adaptation policies and actions to protect health from climate impacts (the black  area in the graph below).

–             Through mitigation, such as reducing emissions in the first place (the dark blue area).

–             Through health co-benefits – reaping health gains from climate-friendly policies and    individual behaviour (the light blue area).

Heat related health issues

Most people enjoy a warm summer’s day, but even for those who love sun and heat the most, very hot temperatures can be dangerous. In recent years, severe heatwaves around the world have led to the deaths of tens of thousands of people External link, either from the effects of heat itself or because of air pollution that heatwaves can generate. In the future, heat-related illnesses are likely to get even worse.

Heat stroke and heat exhaustion will become much more common as temperature rise, especially for those who live in tropical regions or who work outdoor. These has serious repercussions for the elderly and for the obese, who have more difficulties shedding excess heat. People at risk with heart failure and individuals with diabetes are also at increased risk.

Human cooling mechanism:


By burning fossil fuels, we emit ozone to the environment.

Inhaling ozone is bad for our lungs. When ozone contacts our lungs, it causes inflammation that makes it hard to breathe for all people, but especially those with existing lung diseases such as asthma and chronic obstructive pulmonary disease (COPD).

Ozone is formed when by-products of fossil fuel combustion, including oxides of nitrogen (NOx) and volatile organic compounds (VOCs) are exposed to ultraviolet radiation from the sun, as is shown in the figure below.

Wildfires and particulate matter

Because climate change causes heatwaves and more severe droughts, it creates conditions favourable to wildfires. During a particularly hot and dry spell in eastern Europe in 2010, thousands of fires burned an area of forest roughly the size of Indiana (38,600 square miles or ~100,000 square kilometres) burned. The smoke from the fires, however, would have stretched from San Francisco to Chicago. The air pollution produced by the fires killed tens of thousands of people.

When forests burn, they produce smoke that is comprised of many toxic substances, as shown in the image below.

Harmful substances in smoke from wildfires includes acrolein (a lung irritant), carbon monoxide (which can be fatal at high concentrations); formaldehyde, benzene, and polyaromatic hydrocarbons, or PAHs (all of which can cause cancer); and particulate matter (PM).

PM2.5 refers to particulate matter that is 2.5 microns in diameter or smaller in size. You may also see references to PM10, 10 microns in size, which is considered less harmful but can still be dangerous.

Very fine beach sand is about 90 microns in size. Human hair is about 50-70 microns in size. PM ten is under 10 microns, and PM two point five is under 2.5 microns.

PM2.5 is about 1/20th the width of a human hair. Research on PM2.5 has clearly demonstrated that when people breathe it in, it can be deadly, particularly by causing heart attacks and strokes. Worldwide, PM exposures is responsible for millions of deaths each year. PM exposure has also been associated with preterm birth, lung cancer, and a host of other diseases. Exposure to air pollution is the 4th highest-ranking risk factor for death in the world.

Allergies and Asthma

Pollen is a major contributor to seasonal allergies and can cause asthma attacks. Warming temperatures have substantially lengthened the season during which plants that produce allergenic pollen can survive.

At the same time, higher carbon dioxide concentrations in the air are contributing to greater pollen output from ragweed plants.

The pollen production per ragweed plant was 5 grams in the year 1900, 12.5 grams in the year 2000, and will be over 20 grams in the year 2060.

Figure courtesy of Harvard. Data from Rising CO2 and pollen production of common ragweed (Ambrosia artemisiifolia L.), a known allergy-inducing species: implications for public health.

The data shown in the graph are based upon experiments in a lab in which ragweed plants were grown under different carbon dioxide concentrations (280, 370 or 600ppm). The higher the carbon dioxide concentration, the more pollen was produced. Remember, today the atmospheric carbon dioxide concentration is well above 400ppm, which means the amount of pollen produced by ragweed plants may be twice than that at the start of the 20th century.

Other allergenic plants are influenced by elevated carbon dioxide, including poison ivy. Poison ivy has been shown to grow larger and produce more allergenic urshiol (the compound in poison ivy responsible for causing an allergic reaction) when grown under higher carbon dioxide concentrations

The Basics of Vector-borne Disease

Insects are cold blooded creatures (or “ectotherms”), and so must seek out warmer or cooler environments to regulate their body temperatures. The intensification of the water cycle with climate change is particularly relevant to mosquito reproduction which occurs in water. The parasites and viruses carried by insect vectors also are temperature sensitive.

Rainfall can substantially influence risk of vector-borne disease. Research on Dengue in Guangzhou China, Taiwan and elsewhere documents that rainfall is associated with dengue outbreaks. Rain creates pools of water that can be breeding habitat for juvenile mosquitos. However, too much rain can wash away these pools, and with them, the developing mosquitos.

Somewhat counterintuitively, droughts may also promote vector-borne disease outbreaks. During droughts, people may be more likely to use containers to store water, and mosquitos can breed in these containers.

Warming combined with changes in the water cycle have raised concern about how climate change may influence the spread of vector-borne diseases.

Here we will focus on malaria in the next article. Let’s move now on to waterborne diseases.

Waterborne Disease

Greenhouse gas emissions arguably have equal if not greater relevance to the distribution and spread of waterborne diseases as vector-borne diseases around the world. From Vibrio bacteria that cause cholera and other diseases, to ciguatera fish poisoning and shellfish poisoning and harmful algal blooms, warming temperatures and more intense precipitation may favour waterborne disease outbreaks.

The graphic below illustrates how climate related events, such as heavy precipitation, can contribute to outbreaks of waterborne disease. Rainfall washes pathogens contained in animal and human excrement into sewer systems and eventually into local water bodies where water may be drawn from for drinking or crop irrigation. Warmer temperatures may promote growth of pathogens.

Cities and Sewers

Some cities have drain pipes that carry stormwater run-off and sewage together. These so-called combined sewer systems can be found in many cities around the world, particularly those that had systems built in the late 19th and early 20th centuries. At the time of their construction, the amount of sewage and rainfall were less than today. Engineers accounted for the potential of population growth but not necessarily for the heavier downpours occurring with climate change.

When the combined sewer pipes reach capacity, the sewer systems have outfall pipes that drain into local waterbodies to prevent sewage backing up into peoples’ homes and onto streets (see figure below).

Research on cities and regions in the United States with combined sewers may be more likely to have E. coli contaminated water and higher rates of emergency room visits after extreme rainfall events. (For further studies see Patz et al. 2008 External link, Kleidorfer et al. 2009. 2009  and Nilsen et al. 2011).

Even cities with combined sewer systems, however, have been able to substantially reduce discharges of untreated sewage through a variety of actions. These include planting more vegetation and reducing the number of paved surfaces (which keeps more storm run-off out of the sewer system). Sound familiar? It should – these are the same interventions that prevent urban heat islands and so they provide a double dividend to health.

Regardless of sewer system design, heavier rainfall has been shown to promote outbreaks of waterborne diseases, including hepatitis A, cryptosporidiosis, Vibrios, and leptospirosis as well as enteric pathogens, such as E. coli that causes diarrheal disease.

In parts of the world without sewer systems heavier rains also can promote waterborne disease outbreaks but so too can a lack of rain. Infectious pathogens may be more likely to contaminate freshwater supplies when, for instance, water is scarce.


This article shows a part of the health problems we have, and which will rise by the climate change. In the next article, which will be published within the next two weeks, we would like to complete the picture and to draw some conclusion out of it.

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