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Benjamin Franklin once famously wrote that "in this world nothing can be said to be certain, except death and taxes."2 Had Franklin lived in modern times, he might well have amended his notorious quip to state that only three things can be counted as certainties in this world: death, taxes, and climate change. Over the last century, the continuing development of scientific technology and research has forced scientists and policymakers to wrangle with two incontrovertible facts. First, the Earth's climate is changing due to increased levels of atmospheric carbon dioxide and other greenhouse gases.3 Second, these changes are directly attributable to human activity.4
But what constitutes the phenomenon of climate change, and how has it transformed from a groundbreaking scientific theory to a major issue shaping global and national policy today? Modern understanding of climate change began in the 1950s with the work of Dr. Charles Keeling, an American scientist at the Scripps Institute of Oceanography.5 At the start of Dr. Keeling's scientific career, the environmental impact of humanity's increasing reliance on fossil fuels was little more than a curiosity, a question for which scientists simply did not possess the methodology to produce an answer.6 No technology existed that would allow scientists to determine whether increased use of fossil fuels was causing a commensurate increase in carbon dioxide emissions.7 But "as a young researcher, Dr. Keeling built instruments and developed techniques that allowed him to achieve great precision" in measuring carbon dioxide levels.8
In 1956, Dr. Keeling employed those instruments and techniques to pursue research that would lead to a major scientific breakthrough.9 He began taking air samples to measure their volume of carbon dioxide,10 and, through analyzing these samples, he "discovered that the earth itself was breathing":11 that plants in the Northern Hemisphere took in carbon dioxide while they grew in the spring and summer months and then released it back into the environment as they died during the colder winter months.12 This cycle of growth and decay accounted for some seasonal fluctuation in environmental carbon dioxide levels, but, after establishing a permanent research outpost at Hawaii's Mauna Loa Observatory, Dr. Keeling made a far more troubling discovery.13
Analyzing data collected from the Mauna Loa Observatory over a period of years, Dr. Keeling learned...