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The period 900 - 1200 AD has been called the Little Climatic Optimum. It represents the warmest climate since the Climatic Optimum. During this period, the Vikings established settlements on Greenland and Iceland. The snow line in the Rocky Mountains was about 370 meters above current levels. A period of cool and more extreme weather followed the Little Climatic Optimum. A great drought in the American southwest occurred between 1276 and 1299. There are records of floods, great droughts and extreme seasonal climate fluctuations up to the 1400s.
From 1550 to 1850 AD global temperatures were at their coldest since the beginning of the Holocene. Scientists call this period the Little Ice Age. During the Little Ice Age, the average annual temperature of the Northern Hemisphere was about 1.0 degree Celsius lower than today. During the period 1580 to 1600, the western United States experienced one of its longest and most severe droughts in the last 500 years. Cold weather in Iceland from 1753 and 1759 caused 25 % of the population to die from crop failure and famine. Newspapers in New England were calling 1816 the year without a summer.
The period 1850 to present is one of general warming. Figure 7x-1 describes the global temperature trends from 1880 to 1999. This graph shows the yearly temperature anomalies that have occurred from an average global temperature calculated for the period 1951-1980. The graph indicates that the anomolies for the first 60 years of the record were consistently negative. However, beginning in 1935 positive anomolies became more common, and from 1980 to 1999 the anomolies were between 0.2 to 0.4° Celsius higher that the average for the 119 year period of study.
The idea of a global or hemispheric "Medieval Warm Period" that was warmer than today however, has turned out to be incorrect
Originally posted by The_Doctor
seriously they found ancient palm trees under Antarcticas ice
Originally posted by thermopolis
If man is responsible for global warming then how the "heck" does such a genius as AL GORE explain the warming period between 750 and 1200 AD?
Originally posted by Nygdan
[Al Gore is not a climatologist, he is a politician, everyone recognizes this.
Originally posted by Two Steps Forward
I can't believe this is still being argued, but maybe that's because I'm overly optimistic about the learning ability of the average human being.
As far as previous warming periods, there have been many periods in which global climate has warmed. Climate can be driven by orbital forcing mechanisms, such as changes in obliquity, eccentricty, etc. None of those factors explain the current warming trend, which 'just happens' to coincide with man-made increases in global atmospheric CO2 concentrations.
by benevolent tyrant:
An example of this is to recognize, for example, that the ocean levels will be rising. We know this is coming. The Southern ice packs are melting in Antarctica and this will, eventually lead to sea levels rising.
As glaciologist Keith Echelmeyer of the University of Alaska's Geophysical Institute noted in September 1997 ( when Vice President Albert Gore made an issue of glacier recession in Glacier National Park): "To make a case that glaciers are retreating, and that the problem is global warming, is very hard to do. The physics are very complex. There is much more involved than just the climate response." Echelmeyer pointed out that, in Alaska, some large glaciers continue to advance in the very same areas where most are retreating.
The AP story doesn't say (and perhaps the Meier research paper doesn't say either) how the rate of glacier recession varied over the last century. If recession was initially rapid and then slowed, then it is very likely the result of the rapid rise in temperature between 1860 and 1940 as the Earth recovered from the Little Ice Age--and not from any global warming due to higher concentrations of CO2.
And indeed there is some evidence of that. [Added July 7, 2005] The IPCC report Climate Change 2001 (p.128) -- based mainly on data from the World Glacier Monitoring Service in Zurich, Switzerland -- noted that until 1940 major mountain glaciers aroung the world were retreating. After 1940, however, about half of these same 20 glaciers stopped retreating and some were advancing.
The term "scientists" is often used in describing signatories, but the petition  did not require signatories to have a degree, or a degree in a scientific field, or to be working in the field in which the signatory had received a degree. The signatory was not asked to provide the name of his/her current or last employer or job. The distribution of petitions was relatively uncontrolled: those receiving the petition could check a line that said "send more petition cards for me to distribute".
In 2005, Scientific American reported: 
Scientific American took a sample of 30 of the 1,400 signatories claiming to hold a Ph.D. in a climate-related science. Of the 26 we were able to identify in various databases, 11 said they still agreed with the petition —- one was an active climate researcher, two others had relevant expertise, and eight signed based on an informal evaluation. Six said they would not sign the petition today, three did not remember any such petition, one had died, and five did not answer repeated messages. Crudely extrapolating, the petition supporters include a core of about 200 climate researchers – a respectable number, though rather a small fraction of the climatological community.
One newspaper reporter said, in 2005:
In less than 10 minutes of casual scanning, I found duplicate names (Did two Joe R. Eaglemans and two David Tompkins sign the petition, or were some individuals counted twice?), single names without even an initial (Biolchini), corporate names (Graybeal & Sayre, Inc. How does a business sign a petition?), and an apparently phony single name (Redwine, Ph.D.). These examples underscore a major weakness of the list: there is no way to check the authenticity of the names. Names are given, but no identifying information (e.g., institutional affiliation) is provided. Why the lack of transparency?
Originally posted by zappafan1
Two Steps Forward: Wiki???? Where practically anyone can edit it?
Anyway, when Scientific American vets the entire list