https://www.eurekalert.org/pub_releases/2020-01/uoe-asi012020.php
21-Jan-2020
Arctic sea ice can't 'bounce back'
University of Exeter
Arctic sea ice cannot "quickly bounce back" if climate change causes it
to melt, new research suggests.
A team of scientists led by the University of Exeter used the shells of
quahog clams, which can live for hundreds of years, and climate models
to discover how Arctic sea ice has changed over the last 1,000 years.
They found 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 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 "unforced" (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 Dr Paul Halloran, of 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.
"Our study shows 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.
"Today, the climate driver isn't weak volcanic or solar changes - it's
human activity, and we are now massively forcing the system."
Co-author of the study Professor Ian Hall, from Cardiff University,
said: "Our results suggest that climate models are able to correctly
reproduce the long-term pattern of sea ice change.
"This gives us increased confidence in what climate models are telling
us about current and future sea ice loss."
When there is lots of sea ice, some of this drifts southwards and, by
releasing fresh water, can slow the North Atlantic Ocean circulation,
otherwise known as the Atlantic Meridional Overturning Circulation (AMOC).
The AMOC brings warm water from the tropics towards the Arctic, so
slowing it down cools this region and allows sea ice to grow further.
So, 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.
Quahog clams are thought to be the longest-living non-colonial animal on
Earth, and their shells produce growth rings which can be examined to
measure past environmental changes.
Dr Halloran is part of the Global Systems Institute, which brings
together experts from a wide range of fields to find solutions to global
challenges.
The new study is part of a project including Cardiff University, the Met
Office and an international team working on climate model simulations of
the last millennium. The work was funded by the Natural Environment
Research Council.
###
The paper, published in the journal Scientific Reports, is entitled:
"Natural drivers of multidecadal Arctic sea ice variability over the
last millennium."
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