Antarctic sea-ice models improve for the next IPCC report

Date:
June 10, 2020
Source:
University of Washington
Summary:
All the new coupled climate models project that the area of sea
ice around Antarctica will decline by 2100, but the amount of loss
varies considerably between the emissions scenarios.



FULL STORY ==========================================================================
The world of climate modeling is complex, requiring an enormous amount
of coordination and collaboration to produce. Models feed on mountains
of different inputs to run simulations of what a future world might look
like, and can be so big -- in some cases, lines of code in the millions --
they take days or weeks to run. Building these models can be challenging,
but getting them right is critical for us to see where climate change
is taking us, and importantly, what we might do about it.


==========================================================================
A study in Geophysical Research Letters evaluates 40 recent climate
models focusing on sea ice -- the relatively thin layer of ice that
forms on the surface of the ocean -- around Antarctica. The study was coordinated and produced to inform the next Intergovernmental Panel on
Climate Change report, due out in 2021.

All the models projected decreases in the aerial coverage of Antarctic
sea ice over the 21st century under different greenhouse gas emission scenarios, but the amount of loss varied considerably between the
emissions scenarios.

"I am really fascinated by Antarctic sea ice, which the models have
struggled more with than Arctic sea ice," said lead author Lettie Roach,
a postdoctoral researcher at the University of Washington. "Not as
many people are living near the Antarctic and there haven't been as
many measurements made in the Antarctic, making it hard to understand
the recent changes in sea ice that we've observed through satellites."
The models are known as coupled climate models, meaning they incorporate atmospheric, ocean, terrestrial and sea ice models to project what the
future holds for our climate system. We are all familiar with the story
of soon-to-be ice-free summers in the Arctic and the implications that
may have on global trade. But what's driving change around Antarctic
sea ice and what's expected in the future is less clear.

This study's assessment of Antarctic sea ice in the new climate models
is among the first.

"This project arose from a couple of workshops that were polar climate centered, but no one was leading an Antarctic sea ice group," said
Roach. "I put my hand up and said I would do it. The opportunity to lead something like this was fun, and I'm grateful to collaborators across many institutions for co-creating this work." The Antarctic is characterized
by extremes. The highest winds, largest glaciers and fastest ocean
currents are all found there, and getting a handle on Antarctic sea ice,
which annually grows and shrinks six-fold, is critically important. To
put that into perspective, that area is roughly the size of Russia.

The icy parts of our planet -- known as the cryosphere -- have an
enormous effect on regulating the global climate. By improving the
simulation of Antarctic sea ice in models, scientists can increase their understanding of the climate system globally and how it will change over
time. Better sea ice models also shed light on dynamics at play in the
Southern Ocean surrounding Antarctica, which is a major component of
our southern hemisphere.

"The previous generation of models was released around 2012," says Roach.

"We've been looking at all the new models released, and we are seeing improvements overall. The new simulations compare better to observations
than we have seen before. There is a tightening up of model projections
between this generation and the previous, and that is very good news."

========================================================================== Story Source: Materials provided by University_of_Washington. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Lettie A. Roach, Jakob Do"rr, Caroline R. Holmes, Franc,ois
Massonnet,
Edward W. Blockley, Dirk Notz, Thomas Rackow, Marilyn N. Raphael,
Siobhan P. O'Farrell, David A. Bailey, Cecilia M. Bitz. Antarctic
Sea Ice Area in CMIP6. Geophysical Research Letters, 2020; 47 (9)
DOI: 10.1029/ 2019GL086729 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200610102723.htm

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