Old Rocks
Diamond Member
The Earth is presently warming, but we do not know if that is a normal thing. I know in researching the history of Greenland for my book Newbeard the Great, I found out that there were reports of people being able to circumnavigate Greenland prior to the voyage of Columbus. Today that is impossible because of the ice sheet to the north of Greenland. Could it be that conditions in that area were warmer a thousand years ago???
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Ice Isotopes
Analyses of stable isotopes in glacial ice provide records of climate changes at high resolution over long time periods. In the low latitudes, this signal is a combination of temperature and hydrologic variables. In the polar ice sheets, the signal is primarily driven by temperature.
Isotope records from Tibet and the Andes show that the climate of the 20th century was unusual with respect to the preceding 2,000 years. Current understanding does not allow us to separate the temperature part of this signal rigorously, but all evidence indicates Tibet warmed over the last century. Andean climate changes have patterns over space and time that are not yet understood.
Greenland had a pronounced period of warmth around A.D. 1000, a cool period from 1600 through 1900, and a modest 20th century warming. Some coastal sites in Antarctica show 20th century warming but interior sites do not. No Antarctic sites show a warming during medieval times.
Surface Temperature Reconstructions for the Last 2,000 Years