This is why I fear all the volcanic eruptions we’re seeing today.
“The Little Ice Age began in the 1300s due to the cooling effect of massive volcanic eruptions,” says this article on BBC news (30 Jan 2012).
A study led by Dr Gifford Miller at the University of Colorado in Boulder found four explosive volcanic eruptions between about 1250 and 1300 that would have blasted huge clouds of sulphate particles into the upper atmosphere, cooled the Earth for centuries, and triggered glacial expansion.
Although the temperature declined less than 1C globally, parts of Europe cooled more than that, particularly in the winter, which explains the thick layer of ice that formed on the River Thames during so many winters at the time.
Studying ancient plants and glacial sediments at several sites in Canada and Iceland, the scientists determined that the cooling began fairly abruptly between 1250 and 1300, then fell another notch between 1430 and 1455.
Analysis of the later phase of the Little Ice Age also suggests that changes in the Sun’s output, particularly in the ultraviolet part of the spectrum, would also have contributed cooling.
Thanks to Winona Campbell for this link