I read that temperatures were about 4 degrees warmer than now about 1000 years ago, then they cooled to the little ice age in the 17th -18th century and have warmed up since then. What was the  cause of the higher temperatures 1000 years ago and the little ice age?

Published by Joseph Cotruvo, President at Joseph Cotruvo & Associates, Water , Environment and Public Health

I read that temperatures were about 4 degrees warmer than now about 1000 years ago, then they cooled to the little ice age in the 17th -18th century and have warmed up since then. What was the  cause of the higher temperatures 1000 years ago and the little ice age?