Global Warming and Climate Change
Global warming and Climate Change refers to an expected rise in global average temperature due to the continued emission of greenhouse gases produced by industry and agriculture which trap heat in the atmosphere. Higher temperatures are expected to be accompanied by changing patterns of precipitation frequency and intensity, changes in soil moisture, and a rise of the global sea level.
Greenhouse gases in the atmosphere act like the glass in the greenhouse: they are transparent to sunlight, which warms the Earth, but they prevent some heat from escaping into space, keeping Earth warmer than it otherwise would be. A majority of this greenhouse effect is natural, maintaining Earth’s average temperature at about 60oF (15oC). Without the natural greenhouse effect, Earth’s average temperature would be closer to 0oF (-18oC).
The atmospheric concentrations of several greenhouse gases are rising as a result of human activity. Carbon dioxide, the most important human-made greenhouse gas, is released primarily by the burning of fossil fuels like coal, oil, and natural gas. Its concentration has risen by nearly 30% over its value in pre-industrial times. Concentrations of other greenhouse gases have also risen; methane levels have more than doubled and nitrous oxide levels are increasing as well.
There is a world-wide consensus among climate scientists that global average temperature will rise over the next 100 years if the release of greenhouse gases from human activity continues to grow. Assessments by the U.S. National Academy of Sciences and the United Nations’ Intergovernmental Panel on Climate Change (IPCC) project that Earth could experience the fastest warming in the history of civilization during the 21st century. Specifically, according to the IPCC, Earth may warm by 1.8oF to 6.3oF by the end of the next century, potentially making it warmer than at any time since the evolution of modern humans.
Such a global temperature rise would be associated with significant climate change. The difference in global average temperature between modern times and the last ice age — when much of Canada and the northern United States were covered with a thick ice sheet — was only about 9oF. A temperature rise of similar magnitude could have serious, potentially devastating effects on society and ecosystems.
While the pace and magnitude of future climate change are still uncertain, there is widespread agreement among scientists and government officials on the key aspects of global warming. This consensus led to negotiation and signing of the United Nations Framework Convention on Climate Change at the 1992 Earth Summit held at Rio de Janiero. The treaty embodied a voluntary commitment by industrial countries to return their emissions to 1990 levels by year 2000. The treaty was strengthened in 1997 by addition of the Kyoto Protocol which calls for mandatory reductions of emissions by industrial countries (e.g., 7% below 1990 levels for the U.S. based on average emissions for the period 2008-2012).