Global warming is caused primarily by carbon dioxide from burning coal, oil and gas. Certain gases that trap heat are building up in Earth's atmosphere. The primary culprit is carbon dioxide, released from burning coal, oil and natural gas in power plants, cars, factories, etc. (and to a lesser extent when forests are cleared). The second is methane, released from rice paddies, both ends of cows, rotting garbage in landfills, mining operations, and gas pipelines. Third are chlorofluorocarbons (CFCs) and similar chemicals, which are also implicated in the separate problem of ozone depletion (see #5 below). Nitrous oxide (from fertilizers and other chemicals) is fourth. #2 Earth's average temperature has risen about 1 degree F in the past 100 years and is projected to rise another 3 to 10 degrees F in the next 100 years. While Earth's climate has changed naturally throughout time, the current rate of change due to human activity is unprecedented during at least the last 10,000 years. The projected range of temperature rise is wide because it includes a variety of possible future conditions, such as whether or not we control greenhouse gas emissions and different ways the climate system might respond. Temperatures over the US are expected to rise more than over the globe as a whole because land areas closer to the poles are projected to warm faster than those nearer the equator.
#3 There is scientific consensus that global warming is real, is caused by human activities, and presents serious challenges. Scientists working on this issue report that the observed global warming cannot be explained by natural variations such as changes in the sun's output or volcanic eruptions. The most authoritative source of information is the UN Intergovernmental Panel on Climate Change (IPCC) which draws upon the collective wisdom of many hundreds of scientists from around the world. The IPCC projects global temperature increases of 3 to 10 degrees F in the next 100 years and says that human activity is the cause of most of the observed and projected warming.
#4 There's a difference between weather and climate.
Weather refers to the conditions at one particular time and place, and can change from hour to hour, day to day, and season to season. Climate, on the other hand, refers to the long-term average pattern of weather in a place. For example, we might say that the climate of South Florida is warm, moist and sunny, although the weather on a particular day could be quite different than that. Long-term data are needed to determine changes in climate, and such data indicate that Earth's climate has been warming at a rapid rate since the start of intensive use of coal and oil in the late 1800s.
#5 The ozone hole does not cause global warming.
Ozone depletion is a different problem, caused mainly by CFCs (like Freon) once used in refrigerators and air conditioners. In the past, CFCs were also used in aerosol spray cans, but that use was banned in the US in 1978. CFCs deplete the stratospheric ozone layer that protects life on Earth from excess ultraviolet light that can cause skin cancer and cataracts in humans and other damage to plants and animals. An international agreement has phased out most uses of CFCs but the ozone layer is only just beginning to recover, partly because these chemicals remain in the atmosphere for a long time. (Although ozone depletion is not the cause of global warming, there are a number of connections between the two. For example, many ozone-depleting compounds are also greenhouse gases. Some of the compounds now replacing CFCs in order to protect ozone are also greenhouse gases. And ozone itself is a greenhouse gas. In addition, while greenhouse gas build-up causes temperatures close to Earth's surface to rise, it cause temperatures higher up, in the stratosphere, to fall. This stratospheric cooling speeds ozone depletion, delaying the recovery of the ozone hole.)
#6 Global warming will have significant...
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