Climate Change and Human Health

27 April 2008

We were recently asked to "describe a disease or disorder thought to be caused in part by human induced climate change" and to "discuss what portion of its variation is environmental". We chose infectious diseases as our focus. Dr. Robert Shope classified infectious diseases by the number of factors that characterize their spread. A two-factor disease, such as Measles, requires only the Morbillivirus and a human host. As such, two-factor diseases tend to persist wherever human to human transmission is possible, which is truly anywhere two or more people exist and interact and have contact with anyone else. Thus, two-factor diseases tend not to vary greatly with changing environment (Shope, 1991). Though, one dangerous exception can be found in Cholera, a dangerous water-borne illness caused by Vibrio cholerae infection. Incidence of Cholera epidemics increase when harsh storms strike low lying regions. It acts as a 'faux' three-factor disease through fecal/oral transmission amongst members of a community.

However, a true three-factor disease, such as Dengue, uses an intermediate. Flavivirus requires a mosquito (such as Aedes aegypti) to infect a human host. As the intermediate is sensitive to such conditions as mean temperature, humidity and length of breeding season, Dengue and many other similar three and four-factor diseases can and likely will become more widespread with GCC (Shope, 1991). Indeed, as growth zones shift farther North, disease-transmitting insects persist longer and across more inhabited ranges.

Dr. Shope added, "In the special case of segmented genome viruses, ecological overlap of populations creates an abundant opportunity for reassortment of genes that could increase the virulence of the progeny virus. There is no way to anticipate these events, but their potential argues for maintaining a strong biomedical infrastructure and watching closely for new diseases." (Shope, 1991). Thus, human-induced GCC can also yield new viruses by allowing existing ones to overlap and exchange genes in a newly found environment common to both.

The spread of two-factor diseases, such as Cholera, can be effected by climate change. Our immune response to them is generally qualitative. Malaria and other 'three plus' factor diseases, while also responsive to climate change, have a quantitative effect with respect to the genes of their hosts and the environmental factors that promote or inhibit their progress (Mackinnon et al. 2005). Our best defense is to combine strategies that decrease climate change with efforts to monitor the growing ranges and changes available to such diseases.

Mackinnon MJ, Mwangi TW, Snow RW, Marsh K, Williams TN. 2005. Heritability of malaria in Africa. Public Library of Science: Medicine 2(12):e340.

Shope, R. E. 1991. Global climate change and infectious diseases. Environmental Health Perspectives 96: 171-74.
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Response to Dr. Walker's questions

10 April 2008

Our teacher, Dr. Walker, assigned us to briefly discuss what we have learned based on specific interviews (given and read) and chapter 18 (The Cambrian Explosion and Beyond)...

As Nathan said in his response, discussing evolution without thinking of the environment...is really just a waste of time. The only way evolution exists, functions, is because of the environment. That is one thing I hadn't considered before this project, the huge changes our earth has gone through and how it has affected varying species. I actually really enjoyed reading chapter 18 on the Cambrian Explosion. As a kid, like most, this type of stuff was really the most interesting part of science. Imagining old animals, extinctions, and drifting of land masses was amazing! The section on mechanisms for extinction was particularly interesting, and really explained the material fairly and well. As we all know most people do not accept evolution. I have read differing views, and I can see some validity in all areas, empirical or not...but when looking at the facts of the environments history (which we can physical examine!) and how that affects an ever changing present number of species, it seems almost incomprehensible to deny this compelling evidence.

Response to Dr. Walker's questions

10 April 2008

This post is my personal response to our professor’s questions – “what have I learned?” and “why it is important for an environmental scientist to know about evolution?”.

Briefly, I learned from our interview with Dr. Scholes and my readings of Dr. Barnosky’s findings the importance of establishing realistic parameters in evolutionary research. Whether these parameters are temporal, spatial or functional, too broad a range can disguise (“average out”) important results while too narrow a range can yield too small a sample to demonstrate any result at all. Dr. Barnosky tested ever larger ranges of time until one proper to his team’s research interests was found; they broadened the spatial range until it was greater than a single population being studied, yet smaller than an entire biome. Only then did relevant trends become apparent. When I consider the public discourse regarding our impact upon the environment and biodiversity, these methods highlighted instances of flawed reasoning, many of which I was guilty of prior to these experiences.

Additionally, I learned that human activities generally impact the biosphere through greater rates of extinction and the results of such extinction events. Speciation as a result of our impact upon the climate is very unlikely, perhaps impossible, due to the brief range of time we are likely to affect the environment. That very fact is startling as it reminded me of the average lifespan of mammalian species Dr. Barnosky mentioned and our place within it.

Finally, I think it is essential that an environmental scientist be well educated in the mechanisms, trends and effects of evolution, as the environment is in part comprised of all of the living forms within it. Knowledge of evolution is required to understand why the environment was as it was, why it is what it is today, why it is changing, and what it may be in the future. I think that any approach to environmental science in the absence of evolution is like trying to understand a machine comprised of a vast number of unpredictable parts, with no knowledge of what force causes the whole to operate as it does. In this way evolution is a force applied to a ‘medium number system’ (Weinberg 2001) thus, understanding evolutionary forces exempts an environmental scientist from having to know every single part and action amongst this vast number – the trends applied to an appropriately chosen sample are sufficient as the theory of evolution is one of the most successful scientific generalizations ever developed.

-nrw

Weinberg, GM. An Introduction to General Systems Thinking. New York: Dorset House Publishing; 2001. 20 p.