Ocean eddies could explain Antarctic sea-ice paradox
Basis for reliable projections of the impacts of climate change in the Antarctic
Date:
February 2, 2022
Source:
Alfred Wegener Institute, Helmholtz Centre for Polar and Marine
Research
Summary:
Despite global warming and the sea-ice loss in the Arctic, the
Antarctic sea-ice extent has remained largely unchanged since
1979. However, existing climate model-based simulations indicate
significant sea-ice loss, contrary to actual observations. As
experts have now shown, the ocean may weaken warming around
Antarctica and delay sea-ice retreat.
FULL STORY ========================================================================== Despite global warming and the sea-ice loss in the Arctic, the Antarctic
sea- ice extent has remained largely unchanged since 1979. However,
existing climate model-based simulations indicate significant sea-ice
loss, contrary to actual observations. As experts from the Alfred Wegener Institute have now shown, the ocean may weaken warming around Antarctica
and delay sea-ice retreat. Given that many models are not capable of
accurately reflecting this factor and the role of ocean eddies, the
study, which was just published in the journal Nature Communications,
provides the basis for improved simulations and forecasts of the future development of the Antarctic.
========================================================================== Global warming is progressing rapidly, producing effects that can be
felt around the world. The impacts of climate change are especially
dramatic in the Arctic: since the beginning of satellite observation in
1979, the sea ice has declined massively in the face of rising global temperatures. According to the latest simulations, the Arctic could
be consistently ice-free in summer before 2050, and in some years even
before 2030.
Yet on the other side of the planet in Antarctica, the sea ice seems
to have evaded the global warming trend. Since 2010, there have been
more interannual fluctuations than in the previous period. However,
apart from a significant negative excursion in the years 2016 to 2019,
the long-term mean sea-ice cover around the Antarctic continent has
remained stable since 1979. As such, the observable reality does not
match the majority of scientific simulations, which show a significant
sea-ice loss over the same timeframe. "This so-called Antarctic sea-ice
paradox has preoccupied the scientific community for some time now," says
first author Thomas Rackow from the Alfred Wegener Institute, Helmholtz
Centre for Polar and Marine Research (AWI). "The current models cannot
yet correctly describe the behaviour of the Antarctic sea ice; some key
element seems to be missing. This also explains why the Intergovernmental
Panel on Climate Change, IPCC, concludes that the confidence level for model-based projections of future Antarctic sea ice is low." In contrast,
the models are already so reliable in the Arctic that the IPCC ascribes
a high confidence level to their projections. "With our study, we now
provide a basis that could make future projections for Antarctica much
more reliable." In the course of the study, the team applied the AWI
Climate Model (AWI-CM).
Unlike other climate models, the AWI-CM allows certain key regions like
the Southern Ocean to be simulated in far more detail -- or in other
words, in "high resolution." As a result, mixing processes in the ocean,
caused by smaller ocean eddies with diameters of 10 to 20 kilometres,
can also be directly included.
"We used a broad range of configurations for our simulations. In
the process, it became clear that only those simulations with
a high-resolution description of the Southern Ocean encircling the
Antarctic produced delayed sea-ice loss similar to what we are seeing in reality," says Rackow. "When we then extended the model into the future,
even under a highly unfavourable greenhouse-gas scenario the Antarctic
sea-ice cover remains largely stable until mid-century.
After that point the sea ice retreats rather rapidly, just as the Arctic
sea ice has been doing for decades." As such, the AWI study offers a
potential explanation for why the behaviour of the Antarctic sea ice
does not follow the global warming trend. "There could be a number of
reasons for the paradoxical stability of the sea-ice cover. The theory
that additional melt water from the Antarctic stabilises the water
column and thus also the ice by shielding the cool surface waters from
the warmer deep waters is being discussed. According to another theory,
the prime suspects are the westerlies blowing around the Antarctic,
which have been strengthening under climate change. These winds could essentially spread out the ice like a thin pizza dough, so that it
covers a greater area. In this scenario, the ice volume could already
be declining, while the ice-covered areas would give the illusion of stability," Rackow explains.
AWI's research efforts now bring ocean eddies into the focus. These
could play a decisive part in dampening and thus delaying the effects
of climate change in the Southern Ocean, allowing the ocean to
transport additional heat taken up from the atmosphere north, toward
the Equator. This northward heat transport is closely linked to the
underlying overturning circulation in the upper about 1,000 metres of
the ocean, which in the Southern Ocean is driven by the wind on the one
hand but is also influenced by eddies. While the northward component of
the circulation is growing due to stronger westerlies, the simplified
eddies in low-resolution climate models often seem to overcompensate for
this factor by a southward component toward Antarctica; the explicitly simulated eddies in the high-resolution model display a more neutral
behaviour. Taken together, a more pronounced northerly change in heat
transport can be seen in the high- resolution model. As a result,
the ocean surrounding the Antarctic warms more slowly and the ice cover
remains stable for longer. "Our study supports the hypothesis that climate models and projections of the Antarctic sea ice will be far more reliable
as soon as they are capable of realistically simulating a high-resolution ocean, complete with eddies," says Rackow. "Thanks to the ever-
increasing performance of parallel supercomputers and new, more efficient models, next-generation climate models should make this a routine task." ========================================================================== Story Source: Materials provided by Alfred_Wegener_Institute,_Helmholtz_Centre_for_Polar_and
Marine_Research. Note: Content may be edited for style and length.
========================================================================== Journal Reference:
1. Thomas Rackow, Sergey Danilov, Helge F. Goessling, Hartmut
H. Hellmer,
Dmitry V. Sein, Tido Semmler, Dmitry Sidorenko, Thomas Jung. Delayed
Antarctic sea-ice decline in high-resolution climate change
simulations.
Nature Communications, 2022; 13 (1) DOI: 10.1038/s41467-022-28259-y ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2022/02/220202080319.htm
--- up 8 weeks, 4 days, 7 hours, 13 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)