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Introduction - What is Global Warming
Global warming refers to a general rise in the Global Mean Surface Temperature across the Earth. Natural variations in climate between locations on the earth and over periods of time make it difficult to identify general changes except over a long time scale and a large area. A temporary rise or fall in temperature in one place is not evidence for or against a change in the world's temperature.
Global Mean Surface Temperature (GMST) is a measure of the combined land-surface, air and sea surface temperatures. These measurements are taken from a combined average of thousands of thermometers in every country, worldwide, recording temperatures in standard boxes called Stevenson Screens. Work carried out by NASA and the University of East Anglia suggests that the GMST has increased by about 0.5°C since the late 19th century and by about 0.3°C over the last 40 years, which is the period with most reliable data. (NASA GISS, 2004)
Carbon dioxide emissions play an important part in this temperature rise as they act as "greenhouse gases." This means that as the emissions build up in the atmosphere this traps heat generated on Earth, which adds to the effect of the sun's rays and raises the global temperature. (Blake, S., 1998, pp. 70-73)
Measurements of atmospheric CO2 levels taken in Colorado and Antarctica show that the levels have increased sharply over the last fifty years. This increase has matched the general increase in GMST. (Blake, S., 1998, pp. 151-152)
If no steps are taken to reduce global production it is predicted that the amount of CO2 in the atmosphere by the year 2100 will be more than double the current level, and the rate of emission will have almost tripled. Using computer based climate models it has been shown that this increase will have the effect of raising the GMST by between 1.0°C and 3.5°C. (Blake, S., 1998, pp. 154-155)
Blake, S et al., (1998) S103 Discovering Science. Block 2: A Temperate Earth The Open University, Milton Keynes.
NASA Goddard Institute for Space Studies, "NASA GISS: Surface Temperature Analysis" http://www.giss.nasa.gov/data/update/gistemp/, [2004, accessed 15 November 2004]