Volcanic eruptions throw up dust, ash and sulphur dioxide
Outpourings of volcanic ash from Iceland in the 17th Century contributed to a period of famine and hardship in Scotland, according to experts.
A major eruption in 1695 saw large parts of the country affected by a "sulphurous fog".
Prof Alastair Dawson, writing in the latest Scottish Environment Protection Agency magazine, said it came at a time of climatic change.
Dust in the atmosphere dimmed sunlight causing crops to fail.
Prof Dawson, of the University of Aberdeen, writes in Sepa View: "We cannot be sure what the precise effect of this eruption was on Scotland's climate but we do know that the years between AD 1693-1700 were characterised by widespread famine.
"They later became known as the 'King William's Dear Years'.
"A contemporary account of this time describes how it was common for people to bring in the crops in the frosts and snow between November and February."
But he said many crops simply rotted in the fields.
The effect of eruptions on the Highlands and Islands during the 17th Century has been investigated by other academics.
A research paper called: Endemic stress, farming communities and the influence of Icelandic volcanic eruptions in the Scottish Highlands is held in the Lyell Collection of the Geological Society.
In an interview on solar activity with the BBC News Scotland website last April, Gareth Jones - a climate research scientist at the Met Office - said volcanic ash was an important factor in influencing temperatures.
He said volcanic eruptions throw up dust, ash and sulphur dioxide.
In the upper atmosphere, the sulphur dioxide becomes droplets of sulphuric acid and this creates a veil, dimming sunlight.
Mr Jones said volcanoes were more active in the 17th and 18th Centuries than they are today.