Stability check on Antarctica reveals high risk for long-term sea-level
rise

Date:
September 23, 2020
Source:
Potsdam Institute for Climate Impact Research (PIK)
Summary:
The warmer it gets, the faster Antarctica loses ice - and much of
it will then be gone forever. That's what a team of researchers
has found out in their new study on how much warming the Antarctic
Ice Sheet can survive.



FULL STORY ==========================================================================
The warmer it gets, the faster Antarctica loses ice -- and much of it
will then be gone forever. Consequences for the world's coastal cities
and cultural heritage sites would be detrimental, from London to Mumbai,
and from New York to Shanghai. That's what a team of researchers from
the Potsdam Institute for Climate Impact Research, Potsdam University
and New York's Columbia University has found out in their new study,
published in Nature (cover story), on how much warming the Antarctic
Ice Sheet can survive. In around one million hours of computation time,
their unprecedentedly detailed simulations delineate where exactly and at
which warming levels the ice would become unstable and eventually melt
and drain into the ocean. They find a delicate concert of accelerating
and moderating effects, but the main conclusion is that unmitigated
climate change would have dire long-term consequences: If the global
mean temperature level is sustained long enough at 4 degrees above pre- industrial levels, Antarctic melting alone could eventually raise global
sea levels by more than six meters.


========================================================================== "Antarctica holds more than half of Earth's fresh water, frozen in a
vast ice- sheet which is nearly 5 kilometers thick," explains Ricarda Winkelmann, researcher at the Potsdam Institute for Climate Impact
Research (PIK) and University of Potsdam, and corresponding author of
the study. "As the surrounding ocean water and atmosphere warm due to
human greenhouse-gas emissions, the white cap on the South Pole loses
mass and eventually becomes unstable. Because of its sheer magnitude, Antarctica's potential for sea-level contribution is enormous: We find
that already at 2 degrees of warming, melting and the accelerated ice flow
into the ocean will, eventually, entail 2.5 meters of global sea level
rise just from Antarctica alone. At 4 degrees, it will be 6.5 meters
and at 6 degrees almost 12 meters if these temperature levels would
be sustained long enough." Long-term change: it's not rapid, but it's
forever The paper's title refers to the complex physical phenomenon of hysteresis. In this case, that translates into irreversibility. Anders Levermann, co-author and researcher at PIK and Columbia University
describes: "Antarctica is basically our ultimate heritage from an
earlier time in Earth's history. It's been around for roughly 34 million
years. Now our simulations show that once it's melted, it does not regrow
to its initial state even if temperatures eventually sank again. Indeed, temperatures would have to go back to pre- industrial levels to allow
its full recovery -- a highly unlikely scenario. In other words:
What we lose of Antarctica now, is lost forever." The reasons behind
this irreversibility are self-enforcing mechanisms in the ice sheets'
behavior under warming conditions. Co-author Torsten Albrecht lays out:
"In West Antarctica for instance, the main driver of ice loss is warm
ocean water leading to higher melting underneath the ice shelves, which in
turn can destabilize the grounded ice sheet. That makes glaciers the size
of Florida slide into the ocean. Once temperatures cross the threshold
of six degrees above pre-industrial levels, effects from the ice surface
become more dominant: As the gigantic mountains of ice slowly sink to
lower heights where the air is warmer, this leads to more melt at the
ice surface -- just as we observe in Greenland." The fate of New York,
Tokyo, Hamburg is in our hands Ice loss and melting have accelerated significantly over the last decades in Antarctica. The authors however
have explicitly not addressed the question of time scale in their work,
but rather assess the critical warming levels at which parts of the
Antarctic Ice Sheet become unstable. Winkelmann explains this approach:
"In the end, it is our burning of coal and oil that determines ongoing
and future greenhouse-gas emissions and therefore, if and when critical temperature thresholds in Antarctica are crossed. And even if the ice
loss happens on long time scales, the respective carbon dioxide levels
can already be reached in the near future. We decide now whether we
manage to halt the warming. So Antarctica's fate really lies in our
hands -- and with it that of our cities and cultural sites across the
globe, from Rio de Janeiro's Copacabana to Sydney's Opera House. Thus,
this study really is another exclamation mark behind the importance
of the Paris Climate Accord: Keep global warming below two degrees."
Levermann adds: "If we give up the Paris Agreement, we give up Hamburg,
Tokyo and New York."

========================================================================== Story Source: Materials provided by Potsdam_Institute_for_Climate_Impact_Research_(PIK).

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Julius Garbe, Torsten Albrecht, Anders Levermann, Jonathan
F. Donges,
Ricarda Winkelmann. The hysteresis of the Antarctic Ice
Sheet. Nature, 2020; 585 (7826): 538 DOI: 10.1038/s41586-020-2727-5 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200923124706.htm

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