Global warming is the increase in the average temperature of the Earth's near-surface air and oceans since the mid-20th century and its projected continuation. Scientists have determined that a number of human activities are contributing to global warming by adding excessive amounts of greenhouse gases to the atmosphere. Greenhouse gases vary in their ability to absorb and hold heat in the atmosphere, but there are also wide differences between naturally occurring gases. For example, nitrous oxide absorbs 270 times more heat per molecule than carbon dioxide, and methane absorbs 21 times more heat per molecule than carbon dioxide. Greenhouse gases accumulate in the atmosphere and trap the heat that normally would exit into outer space. While many greenhouse gases occur naturally and are needed to create the greenhouse effect that keeps the Earth warm enough to support life, human use of fossil fuels is the main source of excess greenhouse gases. By driving cars, using electricity from coal-fired power plants, or heating our homes with oil or natural gas, we release carbon dioxide and other heat-trapping gases into the atmosphere. Deforestation is another significant source of greenhouse gases, because fewer trees means less carbon dioxide conversion to oxygen.
During the 150 years of the industrial age, the atmospheric concentration of carbon dioxide has increased by 31 percent. Over the same period, the level of atmospheric methane has risen by 151 percent, mostly from agricultural activities such as raising cattle and growing rice.
Global temperatures are expected to increase 3.5 to 8 degrees Fahrenheit by 2050. Rising temperatures will alter global weather patterns that have a direct effect on water supplies and agriculture. Deserts will expand, the frequency and severity of droughts and deadly heat waves will increase, and snow will disappear in most areas—except on the very highest mountain peaks. Sea levels worldwide are expected to rise between 7 to 23 inches by 2100, and will continue to rise for at least the next 1,000 years.
According to a report In the strongest language ever used by the IPCC, the report says that human activity “very likely” has been the primary cause of global warming since 1950. (The term “very likely” indicates more than 90 percent certainty.)
The report summary also says that human activity has been a major contributor to climate change since the Industrial Revolution, which began around 1750.
