Our discussion of biogeochemical cycles shows that they interact strongly, and that they are being substantially altered by human activities. The acidity of precipitation, for example, is a result of the combined influences of SO2, NO3-, and NH3. Nitrate is a powerful oxidant. By oxidizing iron, NO3-influences the cycling of both iron and arsenic in lakes, increasing the mobility of arsenic, a toxic element of considerable importance in the United States.
Human alterations of several global biogeochemical cycles are also warming Earth's climate. One result of this global warming is increasing outbreaks of many diseases. Winter cold typically kills pathogens, sometimes eliminating as much as 99 percent of a pathogen population. If climate warming reduces this population bottleneck, some diseases will become more common. For example, dengue fever is now spreading to higher latitudes where it was formerly absent. Several plant diseases are more severe after mild winters or during periods of warmer temperatures. For example, during a 39-year study in Maine, beech bark cankering caused by a fungus (Nectria spp.) was worse after mild winters or dry autumns. These conditions favor the survival and spread of the beech scale insect, which weakens the trees and predisposes them to fungal infection. The spread of this infection poses a serious problem for the timber industry.
The 1990 Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) paid little attention to risks to human health. In contrast, IPCC's 1996 Assessment Report gave detailed consideration to the potential effects of climate change on human health. Our increasingly interconnected global society enables disease organisms to travel rapidly around the world, as in the case of the SARS virus, which was carried by infected people from China to Canada within a few days. The combination of human mobility and climate warming poses serious challenges to human health throughout the world.
Was this article helpful?
This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.