Youngstown, Ohio: This could end up being the coldest July on record

The average temperature for the Valley for the month so far is 65.9 degrees, 3.7 degrees lower than average, according to National Weather Service statistics.

If it doesn’t warm up, this would be the coldest July on record.

What caused The Arctic Warming of 1919-1939?

In recent years attention is being directed more and more towards a problem which may possibly prove of great significance in human affairs, the rise of temperature in the northern hemisphere, and especially in the Arctic regions. (Brooks, 1938)

At the time of the writing of these lines in 1938, the Arctic had got as warm as in the first decade of the 21st Century. How much do we know about the mechanism that caused the previous arctic warming? Not very much, as Bronnimann et a. acknowledged