Physiological Determinants of Global Health

Malaria and Climate Change

Scientific consensus around human induced climate change is such that all major scientific organizations are in agreement that human activities are impacting global climate by increasing the atmospheric levels of carbon dioxide.¹¹ The following paragraphs supply background information for the teacher.

The atmosphere is a soup of gases, primarily nitrogen (78%), oxygen (21%) and a longer list of minor gases (1%). One of these minor ingredients is carbon dioxide. CO₂ is a simple molecule. It exists as a gas at the standard temperature and pressure found on Earth’s surface. As a gas, CO₂ is one turn in the carbon cycle, returning photosynthetic products back to the atmosphere after respiration, decomposition or combustion. But what makes this gas of special concern? We must first look at the nature of the carbon atom.

Carbon is a non-metal, with an atomic number of six and an atomic weight of 12 (rounded). The most common, and stable isotope ¹²C contains six protons, six neutrons and six electrons swirling around in two orbitals. It is a quadravalent atom; meaning it needs to share four electrons to achieve stability. Being able to form four covalent bonds allows Carbon to create an endless variety of molecules. This factor is what makes it the critical element for our own biological chemistry. Carbon creates the complex structures that form our being, from the backbone of our DNA to the twisted proteins that comprise our bodies. One of the simplest forms in which we find carbon is in carbon dioxide. A single carbon atom bonds with two oxygen atoms, each doubled bonded, resulting in a molecule that looks similar to a Mickey Mouse head balloon.

Ignoring carbon dioxide for just a moment, let’s shift our focus to energy. While we tend to think of planet Earth as a closed system this is not the case. In addition to intergalactic immigrants, such as comets, meteorites and falling dust, every day the Earth is bathed in electromagnetic energy emitted by the Sun. It is the primary energy source for all life on Earth, mainly comprised of visible light passing through the atmosphere and hitting the planet’s surface where it is absorbed. Later on, it is radiated back into space as infrared radiation (IR). The longer wavelengths of IR light do not pass as easily through the atmosphere and some of them are reflected back towards the planet’s surface where they continue to warm the planet. When the amount entering and leaving remain constant the planet’s climate remains stable.

Carbon dioxide in the atmosphere is the main gas that acts to trap the IR radiation responsible for reflecting radiant heat back to the Earth, effectively trapping heat that would otherwise escape into space. This is known as the greenhouse effect. Like Goldilocks’ porridge, our planet is found in a region of habitability where things are not too hot and not too cold. This is a good thing, for it keeps the planet in a temperature zone that allows for the existence of liquid water at the surface - a requirement for life. The planet Venus, however, is an example of the same effect out of control, with average surfaces temperatures on Venus over 860˚ F (460˚C). The Three Bears would complain about more than just chairs and mush if they lived on Venus. Currently, the concentration of CO₂ is at 402 parts per million (ppm) levels not seen on Earth for over 3 million years.¹²

Many human activities contribute to climate change, including the combustion of fossil fuels, clearing of forest habitats and industrial processes such as making steel or concrete. All of these activities release CO₂ into the atmosphere. Using the analogy of an additional blanket on a bed, more CO₂ in the atmosphere causes more heat to be trapped on Earth, causing an increase in the average global temperature.

Climate change contributes to changes in ecosystems. These different examples are all insect related examples that have been recorded in the last ten years. First northbound songbird migrations in the northeastern United States are arriving earlier than previously recorded. This change is hypothesized to synchronize with earlier hatches of insects, a main food source for hatchlings.¹³ A second example of insect populations potentially affected by climate change is the reduced range of honeybees in Europe and North America. The southern edge of their habitat has been shrinking, while their northern edge has not been expanding.¹⁴

It is common knowledge that California is in the middle of its 4^th year of drought, now officially classified as a critical situation and a State of Emergency. What is not as well known is that while widespread and certainly damaging, these regional events are not sufficient as evidence for climate change. The drought however is an example of a high interest news event that can help my students both access this topic as well as discuss the kinds of changes they are observing that impact their own lives..

How will these changes affect mosquito habitat and range? Two specific example provide clues. Nairobi, the capitol city of Kenya was founded in part due to it’s elevation of 1661m, high enough and cool enough to prevent the breeding of Anopheles.¹⁵ How will this city be affected as climate changes and many places experience warming conditions? Will Anopheles now be able to survive where it has not been before? 

Another example is the recent reemergence of malaria on the Korean Peninsula, which has been attributed to climate change, as warmer temperatures provide a longer season for the mosquitos to live.¹⁶