There is some climate information that has only been available in great detail since the advent of satellites in the 1960s. Sea ice extend would be one example, with good information only available since 1979. Snow cover over the globe would be yet another example with a reliable database only going back to 1966. In those 44 years of records, December 2009 ranked as having the second highest aerial extent of snow cover over the Northern Hemisphere. Last month recorded peak snow coverage of nearly 46 million square kilometers (18 million square miles) with an average of 43 million square kilometers (17 million square miles) for the entire month.
Taken alone, North America set a record average December extent with nearly 16 million square kilometers (6 million square miles) of the continent covered by snow. To give some perspective to the abundance of snow cover, on several occasions, nearly two-thirds of the lower 48 states were snow covered last month.