2. Global Warming

    • Invisible gases help to warm the planet by trapping the Sun’s heat and preventing some of it from being reflected back into space; this process is commonly known as the greenhouse effect.

    • Warming of the Earth’s surface and lower atmosphere by the greenhouse effect keeps the Earth from becoming a frozen ball of ice.

    • Carbon dioxide and other heat-trapping gases, such as methane and nitrous oxide, have been increasing in the atmosphere for more than a century as wastes from industry and automobiles are added in the air.

    • By burning coal and oil, humans have increased the amount of carbon dioxide in the Earth’s atmosphere by 30 percent since the industrial revolution.

    • Rising seas, retreating glaciers, melting ice caps, unseasonable warmth and cold, and unusually intense rains, snowstorms and floods are all recent signs of increased temperatures on the Earth.

    • In the 1990s, our world became hotter than it has been for at least a thousand years; most scientists attribute at least some of the recent rise in temperature to greater emissions of greenhouse gases by human activity.

    • Supercomputer models forecast that the Earth will become noticeably hotter as the result of the unrestrained emission of heat-trapping gases by humans over the next 100 years. But uncertainties in the role of oceans, water vapor and clouds result in a wide range for the predicted temperature increase and possible climate change.

    • The amount of the Sun's life-sustaining radiation that reaches the Earth, known as the solar constant, varies over the 11-year solar cycle of magnetic activity. Greater activity on the Sun makes our planet hotter, and lower solar activity results in a colder Earth.

    • Natural variations in the intensity of the Sun’s radiation can explain many of the temperature fluctuations observed during past centuries, but global warming by heat-trapping gases, emitted by human activity, is required to explain the sharp rise in global temperatures during the 1990s.

    • If current emissions of carbon dioxide and other greenhouse gases go unchecked over the next 100 years, global warming could produce agricultural disaster in the world’s poorest countries, rising seas with coastal flooding throughout the world, and the spread of diseases carried by mosquitoes.

    • The politicized debate over global warming is hampered by scientific uncertainties in predicting its future consequences, and by persons who selectively adopt the scientific forecasts that bolster their case.

    • An international agreement to limit the human emission of heat-trapping gases, known as the Kyoto Protocol, is unlikely to be ratified by rich industrial nations because it is perceived as a threat to their economies and also because fast-developing poor countries are exempt from mandatory emission constraints.

Copyright 2010, Professor Kenneth R. Lang, Tufts University