Snowflakes falling through the atmosphere have the same temperature as the surrounding air. The ice formed from these snowflakes conducts heat very badly, and its original temperature is retained for thousands of years. Shown are (A) The temperature of air over Greenland in the last 8,000 years where the so-called Holocenic Warming (3,500 to 6,000 years ago) is visible; (B) Our epoch, showing the Middle Ages Warming (900-1100) and the Little Ice Age (1350-1880).
Source: D. Dahl-Jensen, et al., 1998. "Past Temperatures Directly from the Greenland Ice Sheet." Science, Vol. 282, No. 9 (October), pp. 268-271