At http://phys.org/print323856790.html … there is a report on study that derives from an ice core section. It was analysed for various chemical traces in a laboratory (several cores from different locations on Antarctica) and the results are said to be an accurate and precise recontruction of historic volcanic sulphate emissions – in the southern hemisphere.
It is published in Nature Climate Change and is a record of the last 2000 years. The Phys Org piece doesn't tell us much about the implications but over at http://tallbloke.wordpress.com/2014/07/06/new-ice-core-sulphate-records-… … which appears to refer to volcanic aerosols causing an opaque sky. Tall Bloke does not mention heavy meteoric activity as a possible source of atmospheric dust – but we can't have everything. What emerges from his take on the study is that massive volcanoes in 1257 and 1488 did not deposit as much sulphate as expected – therefore they had a weaker cooling effect than previously claimed. This is important as in 1258AD there was supposed to have been lots of dust in the atmosphere that led, due to crop failure to a major famine event in Britain. Tall Bloke, however, says that climatic variations at these times were really due to solar factors – or that the role of the Sun running in the background had a bigger role to play than climate scientists allow.