Global temperature measurements show that the earth has warmed significantly since the early 20th century, and especially since the mid-1960s. Record-breaking global temperatures have become common, with 2005, 2010, 2014, and 2015 each setting successive high-temperature records. Of note, 15 of the 16 warmest years since 1880 have occurred during the 21st century. During 2015, the global land temperature was 0.9° C warmer than the 20th century average. Mean global ocean temperatures also set new records in 2015, with an annual average temperature 0.74° C above the 20th century average. As of this writing, 2016 is on track to approach or exceed the records just set in 2015.
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The rising atmospheric and ocean temperatures have led to a large number of effects that include changes in storm frequency, drought, and flood, as well as large-scale ice losses in Greenland, Antarctica, and the vast majority of the other glaciated regions on earth, as well as dramatic thinning or disappearance of Arctic ocean sea ice. The melting of land-based glacial ice and the thermal expansion of the warming oceans has produced approximately 80 mm of global average sea level rise since 1993, and the sea level currently is rising at a global average rate of 3.5 ± 0.4 mm/year.
Although politicians quibble, among scientists there is a general acceptance that climate change is, at least in part, man-made. The culprit is the rising atmospheric level of greenhouse gases, particularly carbon dioxide (CO2) released through the burning of fossil fuels (
Fig. 8.1A ), as well as ozone (an important air pollutant, discussed later), and methane. These gases, along with water vapor, produce the so-called “greenhouse effect” by absorbing energy radiated from Earth’s surface that otherwise would be lost into space. The annual average level of atmospheric CO2 (about 401 ppm) in 2015 was higher than at any point in approximately 650,000 years and, without changes in human behavior, is expected to increase to 500 to 1200 ppm by the end of this century—levels not experienced for tens of millions of years. This increase stems not only from increased CO2 production but also from deforestation and the attendant decrease in carbon fixation by plants. Depending on the computer model used, increased levels of greenhouse gases are projected to cause the global temperature to rise by 2°C to 5°C by the year 2100 (
Fig. 8.1B ). The health consequences of climate change will depend on its extent and rapidity, the severity of the ensuing consequences, and humankind’s ability to mitigate the damaging effects. Even in the best-case scenario, however, climate change is expected to have a serious negative impact on human health by increasing the incidence of a number of diseases, including the following:
Cardiovascular, cerebrovascular, and respiratory diseases, all of which will be exacerbated by heat waves and air pollution.
Gastroenteritis, cholera, and other foodand waterborne infectious diseases, caused by contamination as a consequence of floods and disruption of clean water supplies and sewage treatment, after heavy rains and other environmental disasters.
Vector-borne infectious diseases, such as malaria and dengue fever, resulting from changes in vector number and geographic distribution related to increased temperatures, crop failures, and more extreme weather variation (e.g., more frequent and severe El Niño events).
Malnutrition, caused by changes in local climate that disrupt crop production. Such changes are anticipated to be most severe in tropical locations, in which average 1958-2015 Correlation Coefficient: 0.90947 –0.4 –0.2 0 0.2 0.4 0.6 0.8 A Global temperature anomaly (° C)