An international research team studied ancient plants from Iceland and Canada, and sediments carried by glaciers. Scientists conclude that little Ice Age was caused by the cooling effect of gigantic volcanic eruptions, and continued by changes in Arctic ice cover. The global plunge in temperatures was less than 1C, but parts of Europe refrigerated more, mainly in winter, with the River Thames in London frozen densely enough to be negotiable on foot.
The scientists studied a number of sites in north-eastern Canada and in Iceland where small icecaps have expanded and contracted over the centuries. When the ice spreads, plants beneath are killed and entombed in the ice. Carbon-dating can decide how long before this happened. Aerosols from volcanic eruptions usually cool the climate for just a few years. The additional ice in turn reflected more solar emission back into space, and destabilized the Atlantic Ocean circulation usually known as the Gulf Stream.