London: A large-scale volcanic event caused the Ice age during the Jurassic period nearly 170 million years ago, say researchers.

An international team of experts, including researchers from University of Exeter, found evidence of a large and abrupt cooling of the Earth’s temperature during the Jurassic Period which lasted millions of years.

The scientists found that the cooling coincided with a large-scale volcanic event – called the North Sea Dome – which restricted the flow of ocean water and the associated heat that it carried from the equator towards the North Pole region.

The team suggest that it is this volcanic event, preventing the ocean flow, rather than a change in CO2 in the atmosphere (which causes today’s climate change), that led to an extended ice age in a period more synonymous with very warm conditions.

“We tend to think of the Jurassic as a warm ‘greenhouse’ world where high temperatures were governed by high atmospheric carbon dioxide contents. The new study suggests that re-organisation of oceanic current patterns may also have triggered large scale climate changes,” explained professor Stephen Hesselbo.

Rather than the seven continents that cover Earth’s surface today, during the Jurassic Period, there was one single “supercontinent” called Pangaea.

This “supercontinent” had a broad seaway across it that connected a north polar sea to a warm equatorial ocean.

The team of scientists spent 10 years constructing a record of seawater temperature change using fossil mollusc shells.

They found that during the same period that the North Sea Dome event occurred, the Earth experienced a significant and fast cooling in temperature.

The team have hypothesised that this volcanic event restricted the poleward flow of ocean water and associated heat, flipping the northern hemisphere from a very warm climate to a cold climate state.

The evidence indicates that this cold period lasted many millions of years, until the North Sea Dome subsided.

“This work suggests a mechanism at play that may also have been important for driving other climate change events in the Jurassic and at other times in Earth history,” added Hesselbo in a paper that appeared in the scientific journal Nature Communications.