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<b>Earth Gets a Warm Feeling All Over</b><br /><br />LINK<br /><br />Last year was the fourth warmest year on average for our planet since the late 1800s, according to NASA scientists. <br /><br />To determine if the Earth is warming or cooling, scientists look at average temperatures. To get an "average" temperature, scientists take the warmest and the coolest temperatures in a day, and calculate the temperature that is exactly in the middle of those high and low values. This provides an average temperature for a day. These average temperatures are then calculated for spots all over the Earth, over an entire year. <br /><br />Scientists use temperatures taken on land and on surfaces of the oceans. Weather stations provide land measurements, and satellites provide sea surface temperature measurements over the ocean. These data are computed by NASA. The end result recreates and calculates global temperatures, and helps scientists study climate change. Makiko Sato of NASA's Goddard Institute for Space Studies (GISS), New York, converted all the data into readable global temperature maps that provided the means to see the warming.<br /><br />James Hansen of NASA GISS analyzed the data and said that the 2004 average temperature at Earth's surface around the world was 0.48 degrees Celsius or 0.86 Fahrenheit above the average temperature from 1951 to 1980.<br /><br />Global temperatures vary from year to year and place to place, but weather stations and satellite data provide accurate records. By recording them over time, scientists develop a record of the climate, and have been able to see how it's been changing. <br /><br />Some of the changes in climate are due to short-term factors like large volcanic eruptions that launched tiny particles of sulfuric acid into the upper atmosphere (stratosphere) in 1963, 1982, and 1991. These natural events can change climate for periods of time ranging fro