Even as Europe and Siberia was experiencing its coldest November in decades, NASA's Goddard Institute for Space Studies announced that 2002 was the second warmest in climate recording history (Figure 1). Is that true, or is something else involved? NASA asserts:

The 2002 meteorological year is the second warmest year in the period of accurate instrumental data (since the late 1800s). The global surface temperature for 12 months from December 2001 through November 2002 is 0.51°C above the climatological mean (1951-1980 average) in the GISS analysis, which uses meteorological station measurements over land and satellite measurements of sea surface temperature over the ocean.

But there is something NASA isn't telling you. This data comes from ground based temperatures --- usually measured by thermometers at airports. That presents a problem. Besides being moved a few times in their history and data being taken by an infinite number of people, all but a few of these stations in the first half of the twentieth century were surrounded by open countryside. The cities served by these airports  expanded beyond the airports in the latter half of the twentieth century -- especially from the mid-1970s on. The airports, and therefore the thermometers, are now surrounded by asphalt, tar-paper roofs and tall buildings that trap heat.

The surrounding or ambient temperature has therefore increased substantially because dark non-living surfaces trap and radiate more energy than living green surfaces. This is called the heat-island effect. When the ground data is compared against satellite data from nine geo-stationary microwave measuring sensors that sum the total tropospheric (about 5 miles deep) temperatures for the entire world the results are quite different, as depicted in Figure 2.

Global warming advocates claim a 5 mile deep mass of air is too much to determine if we have global warming. Global warming skeptics say it doesn't matter. If there is real warming, then the entire troposphere should warm. So far that warming is minimal and can be explained by the recovery from the little ice age in the 1700s when it was a full degree cooler than now. Besides, skeptics claim, the earth was a full degree warmer than today around 1200, during what is known as the climatic optimum, when the Vikings colonized and raised crops in Greenland.

The heat island effect is well known by NASA, and climatologists have attempted to correct the data for the United States. When that is done, the data for the United States more closely matches the satellite data. However, except some correction for Europe, little correction has been made for the rest of the world's data. Therefore, the data shown by NASA is highly skewed towards artificial warming. Besides, just how much correction can be used for the ground data? How do they know when enough correction has been applied since there is no benchmark to compare too? Fact is, the scientists can't know how much correction to apply. Therefore, any correction they apply is merely a best guess estimate.