ANTHROPOGENIC CLIMATE CHANGE
Like any other species, humans have always affected, and in turn been affected by, their environment. But with the dawn of agriculture, the ability of H. sapiens to alter the Earth increased dramatically, and reached even greater levels during the Industrial Revolution, which began in the mid- to late 1700s. Since that time, habitat destruction, invasive species introductions, and extinctions have continued and accelerated. But in the last few decades it has become increasingly apparent that industrialization is driving another and potentially greater threat to the Earth’s biota – anthropogenic climate change or global warming. Certain gases in the Earth’s atmosphere trap the sun’s radiation, preventing it from being reradiated, a phenomenon known as the “greenhouse effect.” It is this greenhouse effect that keeps the Earth’s temperature high enough to support life. But since the Industrial Revolution, fossil
fuel use has increased the amount of greenhouse gases, particularly CO2, in the atmosphere. Evidence has increasingly pointed to this rise in greenhouse gas emissions (Fig. 8.12) as a
major factor in global climate change and an overall warming trend that has the potential to cause catastrophic disruption of the Earth’s biosphere.
Figure 8.12: Fossil fuel related carbon dioxide (CO2) emissions over the 20th century. (Wikipedia ‘Global warming;’ Attribution: U.S. Environmental Protection Agency)
Studies of the potential effects of increased atmospheric CO2 go back over a century. In 1896, Swedish physical chemist Svante Arrhenius suggested, and attempted to calculate, how changes in atmospheric CO2 levels could affect temperatures at the Earth’s surface via the greenhouse effect. While the details of his predictions were inaccurate, Arrhenius was one of the earliest scientists to show that the possibility of anthropogenic global warming should be taken seriously.
Debate among climate scientists regarding the potential role of atmospheric gases in climatic change continued throughout the 20th century. By the early 1970s, it was apparent that aerosols were increasing in the atmosphere, but there was disagreement regarding whether these increased aerosols would likely result in global warming or cooling. Although the scientists who predicted cooling were a small minority, their views were exaggerated by the mainstream media. By the 1980s, it was becoming increasingly clear that any cooling effect that might result from atmospheric aerosols would be negligible compared to the heating
of the Earth’s climate due to atmospheric CO2 levels. Climate models indicated a positive relationship between atmospheric CO2 and global temperatures. In 1985, a Franco-Soviet study of Antarctic ice cores, led by Claude Lorius, showed that past temperatures and CO2 levels had tracked each other closely, providing important evidence for a CO2-temperature relationship independent of computer climate models.