Medieval weather records, including details from monks' diaries are helping experts work out how and why climates have changed over the past 500 years.
Edinburgh University scientists found the historic data, such as harvest records, matched modern computer simulations of climate patterns.
Researchers have assembled climate models to account for past events.
They expect the models to work well for forecasting future climate conditions, especially predicting temperatures.
Greenhouse gas emissions will have more of an impact in shaping future climate change.
Professor Gabi Hegerl, of Edinburgh University's school of geosciences, said current human behaviour is "definitely going to shape the climate in a significant and visible way".
She said: "Our work shows that external influences on the weather are important, and that even small changes in factors outside the climate system have a significant effect.
"The climate models seem to be working quite well for the past, so we should expect that, at least when it comes to temperature, they will do well for the future. It indicates that the predictions might be on target."
She added that the archives revealed a considerable amount of interesting information, particularly relating to the last 300 years.
She said: "500 years ago ago, the records were quite sparse, but there is a lot of data going back to the 19th Century and quite a lot of data from the 17th and 18th centuries.
"About 1675 it gets quite sparse. Before that, we're working from monks' diaries and harvest records and all kinds of indirect evidence about whether they experienced warm or cold summers and winters.
"The records are much more accurate when you go past 1675 and the good thing is a lot of interesting things happened after that time.
"About 1700 and the early 19th Century, for example, there were very cold winters. That's been captured quite well in the records."
The computer simulations took account of influences on the weather, such as volcanic activity, variations in the sun's temperature and, more recently, an increase in greenhouse gases.
The study was carried out by the University of Edinburgh in collaboration with the Justus-Liebig University of Giessen in Germany, and the Universities of Bern and Madrid.
The study, supported by the Natural Environment Research Council, the US National Science Foundation and the European Union, was published in the journal Nature Geoscience.