Cosmic rays, being shot across the universe when a star dies and explodes then rain ions down onto Earth, could spark a new Ice Age.
The charged particles from cosmic rays pull water and sulphuric acid together to form clusters, and when these clusters get large enough they can form clouds.
And as more clouds form, the climate cools which can have an impact on long term weather cycles, researchers have said.
The study, which involved observing cosmic rays from the sun hitting the Earth’s atmosphere, found the phenomenon is linked to the Medieval Warm Period around year 1000AD and the Little Ice Age which spanned from the 13th to 17th century.
During the Little Ice Age, the River Thames regularly froze over during the winter.
Dr Henrik Svensmark, lead author of the study, said: “Finally we have the last piece of the puzzle explaining how particles from space affect climate on Earth.
“It gives an understanding of how changes caused by Solar activity or by supernova activity can change climate.”
Dr Hamish Gordon, from the Institute for Climate and Atmospheric Science at the University of Leeds, said: “This is an interesting and plausible result, and if it stands up to more detailed scrutiny it may prove an important contribution to aerosol microphysics.”
The sun follows cycles of roughly 11 years where it reaches a solar maximum and then a solar minimum.
During the former, the Sun gives off more heat, and less in the latter.
Currently, we are in a solar minimum, and the researchers say that this will lead to a colder planet.
The team state: “When the Sun is lazy, magnetically speaking, there are more cosmic rays and more low clouds, and the world is cooler.”