Arctic sea ice can't 'bounce back': Study

The melted sea ice in the Arctic cannot "quickly bounce back" even if climate change is slowed or reversed, according to a study.

Scientists led by the University of Exeter in the UK used the shells of quahog clams, which can live for hundreds of years, and produce growth rings that can be examined to measure past environmental changes.

They also analysed climate models to discover how Arctic sea ice has changed over the last 1,000 years.

The team found that sea ice coverage shifts over timescales of decades to centuries -- so shrinking ice cannot be expected to return rapidly if climate change is slowed or reversed.

The study, published in the journal Scientific Reports, examined whether past ice changes north of Iceland were "forced" -- caused by events such as volcanic eruptions, and variations in the Sun's output -- or part of a natural pattern.

At least a third of past variation was found to be "forced" -- showing the climate system is "very sensitive" to such driving factors, according to lead author Paul Halloran from the University of Exeter.

"There is increasing evidence that many aspects of our changing climate aren't caused by natural variation, but are instead 'forced' by certain events," he said.

The study underlines the large effect that climate drivers can have on Arctic sea ice, even when those drivers are weak as is the case with volcanic eruptions or solar changes, the researchers said.

"Today, the climate driver isn't weak volcanic or solar changes -- it's human activity, and we are now massively forcing the system," Halloran said.

"Our results suggest that climate models are able to correctly reproduce the long-term pattern of sea ice change," said co-author of the study, Ian Hall, a professor at the Cardiff University in the UK.

When there is lots of sea ice, some of it drifts southwards, the researchers said.

By releasing fresh water, this process can slow the North Atlantic Ocean circulation, otherwise known as the Atlantic Meridional Overturning Circulation (AMOC), they said.

The AMOC, researchers noted, brings warm water from the tropics towards the Arctic, so slowing it down cools this region, and allows sea ice to grow further.

With less ice, the AMOC can bring in more warm water -- a so-called "positive feedback" where climate change drives further warming, and sea ice loss.