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+d- t tt., t 'S5S k _ ? ? S,P i F i Flt qt, 1. INTRODUCTION 6 A. UNDERSTANDING CLIMATE CHANGE Scientists around the globe have been working to- gether for decades to track the increase of greenhouse gases in the Earth's atmosphere, rising temperatures and extreme weather. They agree that the planet is warming much more than under natural conditions, and the cause is human activity - primarily the burning of fossil fuels. Earlier this year, the Intergovernmental Panel on Climate Change (IPCC), which includes hundreds of scientists worldwide and was awarded the Nobel Peace Prize last month, issued three new reports on climate change. The key statements are: "Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level." "Most of the observed increase in globally averaged temperatures since the mid-201h Century is very like- ly due to the observed increase in [human-caused] greenhouse gas concentrations." How greenhouse gases work to raise temperatures: Three greenhouse gases produced by natural processes and human activity - carbon dioxide, methane and nitrous oxide - make up less than I percent of Earth's atmosphere, but they exert powerful control over global temperatures. The greenhouse gases absorb the sun's heat as it radiates back from the Earth's surface toward space, and trap that heat in the atmosphere. Over the past 650,000 years, the average concentra- tions of greenhouse gases maintained by nature gave the planet a balanced climate that fostered bountiful ecosystems and eventually civilization and agricul- ture. Greenhouse gas concentrations went up and down with the natural cycle of ice ages, but were never higher than 300 parts per million (ppm). The last century and a half of industrialization changed the balance. Billions of tons of carbon, once safely stored deep underground in the form of coal, oil and gas, are being released into the atmosphere. About 80 percent of human-produced greenhouse gases are released from the burning of fossil fuels. The other 20 percent comes from burning tropical forests and from agriculture and landfills. In the air or by combustion, carbon mixes with oxygen to form carbon dioxide, or COV Of all greenhouse gas emissions resulting from human activity, CO2 makes up about 75 percent. Worldwide, we are releasing 7 billion tons of carbon per year into the atmosphere. Ice cores drilled in Antarctica show that greenhouse gas concentrations started spiking in the late 1800s, at the time of the Industrial Revolution. At that time, the atmosphere held 280 ppm of CO 2' By 2006, CO2 concentrations reached 382 ppm, a 35 percent increase and by far the highest level in all of human history. In the last decade alone, we increased the concentration of CO2 in the atmosphere by 19 ppm. As a result, the global average temperature increased by 1.4 degrees Fahrenheit (F.) in the last century. That may not seem like much, but scientists are observ- ing many examples of rapid, destructive changes in ecosystems worldwide from that increase. Scientists project the global temperature will continue to rise - the question is by how much. The IPCC developed a range of future scenarios based on no new policies to stabilize or reduce greenhouse gas emissions. Under these "business as usual" scenarios, greenhouse gas concentrations could reach 600 to 1,000 ppm by the end of this century, resulting in global temperature increases of 3.6 to 10.4 degrees F.