Global Warming
Global warming is the gradual rise of the earth's near-surface temperature over approximately the last hundred years. The best available scientific evidence—based on continuous satellite monitoring and data from about 2,000 meteorological stations around the world—indicates that globally averaged surface temperatures have warmed by about 0.3 to 0.6°C since the late nineteenth century. Different regions have warmed—some have even cooled—by different amounts. Generally, the Northern Hemisphere has warmed to a greater extent than the Southern Hemisphere, and mid to high latitudes have generally warmed more than the tropics.
Since the advent of satellites, it has become possible for scientists to thoroughly monitor the earth's climate on a global scale. To examine the historical climate record, however, scientists have to use earlier, sparser forms of measurement, such as long-standing temperature records and less exact "proxy" data, such as the growth of coral, tree rings, as well as information from ice cores, which contain trapped gas bubbles and dust grains representative of the climate in which they were deposited. The bubbles in these cores contain oxygen, particularly oxygen isotopes 180 to 160, which are sensitive to variations in temperature. From the ratio between these isotopes at varying ice depths scientists can reconstruct a picture of the temperature variations over time in specific locations. Greater measurement uncertainty surrounds the earlier parts of this record because of sparse coverage (especially in ocean regions). Despite this uncertainty, the balance of scientific evidence confirms that there has been a discernable warming over the last century.
Since the advent of satellites, it has become possible for scientists to thoroughly monitor the earth's climate on a global scale. To examine the historical climate record, however, scientists have to use earlier, sparser forms of measurement, such as long-standing temperature records and less exact "proxy" data, such as the growth of coral, tree rings, as well as information from ice cores, which contain trapped gas bubbles and dust grains representative of the climate in which they were deposited. The bubbles in these cores contain oxygen, particularly oxygen isotopes 180 to 160, which are sensitive to variations in temperature. From the ratio between these isotopes at varying ice depths scientists can reconstruct a picture of the temperature variations over time in specific locations. Greater measurement uncertainty surrounds the earlier parts of this record because of sparse coverage (especially in ocean regions). Despite this uncertainty, the balance of scientific evidence confirms that there has been a discernable warming over the last century.
