§ 2. The Basics of Climate Change § 2. The Basics of Climate Change

• Jurisdiction: United States

§ 2. The Basics of Climate Change

Policy makers trying to deal with climate change must deal with complex scientific issues that usually have major uncertainties associated with any conclusions. The most important questions concern whether global warming is occurring and is it substantially related to human generated GHG emissions, particularly carbon dioxide releases from the combustion of fossil fuels. If uncertainties exist, who should bear the burden of proof, those who advocate business as usual or those who advocate GHG reductions? A noted scholar has written "catastrophic risks deserve some kind of precautionary principle." But efforts to avert catastrophic harm should not be used if they give rise to other risks of catastrophic harm. "Even for the Catastrophic Harm Precautionary Principle, the costs matter."²² This advice is well worth pondering when studying

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both the science and proposed solutions for climate change because climate change involves both high risks and high response costs.

The average temperature of the earth has varied within a range of about 3 degrees C for the last 3000 years. Solar radiation varies and correlates well with temperature variations on earth and provides one theory to explain variations in the earth's temperature. Average global surface air temperatures appear to have increased 0.74 degrees Celsius (C) in the last 100 years (1906-2005), which is larger than the prior reported increase of 0.6 degrees C for 1901-2000. However, the earth's average temperature remains about 1 degree C below the warm period about 1000 years ago known as the Medieval Climate Optimum. The earth's temperature subsequently decreased after the year 1200 leading to the period known as the "Little Ice Age" that lasted from about 1350 to 1850. Then the planet gradually warmed to today's temperature.

Climate models show a trend of increasing temperatures since 1840, although most of the human use of fossil fuels did not occur until after 1940. The United States had temperature spikes in the 1920s before hydrocarbon use significantly increased. From the late 1940s to about 1975 CO₂ levels increased while temperatures decreased. Since then temperatures have been increasing.²³ In the late 1960s and early 1970s concern was expressed over the dangers of global cooling. On June 24, 1974, Time Magazine had an article titled "Another Ice Age?" which included the following: "the atmosphere has been growing cooler for the past three...