From www.friendsofscience.org comes this section:
MYTH 1: Global temperatures are rising at a rapid, unprecedented rate.
FACT: Accurate satellite, balloon and mountain top observations made over the last three decades have not shown any significant change in the long term rate of increase in global temperatures. Average ground station readings do show a mild warming of 0.6 to 0.8C over the last 100 years, which is well within the natural variations recorded in the last millennium. The ground station network suffers from an uneven distribution across the globe; the stations are preferentially located in growing urban and industrial areas (“heat islands”), which show substantially higher readings than adjacent rural areas (“land use effects”).
There has been no catastrophic warming recorded.
MYTH 2: The “hockey stick” graph proves that the earth has experienced a steady, very gradual temperature increase for 1000 years, then recently began a sudden increase.
FACT: Significant changes in climate have continually occurred throughout geologic time. For instance, the Medieval Warm Period, from around 1000 to1200 AD (when the Vikings farmed on Greenland) was followed by a period known as the Little Ice Age. Since the end of the 17th Century the “average global temperature” has been rising at the low steady rate mentioned above; although from 1940 – 1970 temperatures actually dropped, leading to a Global Cooling scare.