*[Enwl-eng] Has Antarctica entered a new state?
ENWL
enwl at enw.net.ru
Thu Sep 21 00:14:12 MSK 2023
+ why it matters to the rest of the world No images? Click here
While the UN convenes a summit on raising national ambitions to tackle global heating – in which several leaders of the biggest polluters are absent – dramatic changes are underway in Antarctica which suggest Earth's climate system is unravelling.
Here in the planet's far south, sea ice surrounding the frozen continent has shrunk so rapidly that there is no precedent in nearly half a century of measurements. As ocean and air temperatures around the Antarctic rise, the region may be entering an entirely new state – with profound consequences for the rest of the world.
You're reading the Imagine newsletter – a weekly synthesis of academic insight on solutions to climate change, brought to you by The Conversation. I'm Jack Marley, energy and environment editor. This week, we're focusing on Antarctica: Earth's refrigerator in meltdown.
"Something has fundamentally changed Antarctic sea ice this year," say Edward Doddridge and Ariaan Purich, a physical oceanographer at the University of Tasmania and a lecturer in climate variability and change at Monash University.
"For many years, while the Arctic lost sea ice, the Antarctic did not. Then, in the spring of 2016, Antarctic sea-ice coverage dropped dramatically. Over two years, the Antarctic lost as much sea ice as the Arctic had lost in three decades. Since then, Antarctic sea ice has been below average almost constantly."
A particularly strong El Niño – the warm phase of a natural fluctuation in Earth's climate – has amplified the background rate of global warming and shattered records worldwide in 2023, from extreme heat to deadly storms.
Antarctica is no exception. Antarctic sea ice reached its lowest recorded extent on February 19: 1.77 million square kilometres, 36% below the 1977-2022 average for the summer minimum.
Doddridge compares the rhythmic contraction and expansion of this sea ice to a heartbeat. The last two summers in Antarctica have seen it retreat further than ever before – a skip in the beat.
"And just as a change in our heartbeat affects our whole body, a change to sea ice around Antarctica affects the whole world," he says.
The continent has been enduring a long and dark winter in recent months. But something is wrong say Doddridge and Purich:
"Ever since we’ve had satellites to measure it, the surface of the ocean has reliably frozen into sea ice at about the same pace every winter, even following low sea ice summers. Except for this year."
At a time when the area of floating sea ice around the continent should be rapidly expanding, the refreeze has proceeded in slow-motion according to Ella Gilbert and Caroline Holmes, polar climate scientists at the British Antarctic Survey.
"There is now an area of open ocean bigger than Greenland. If the 'missing' sea ice were a country, it’d be the tenth largest in the world," they say.
'The new abnormal'
If Antarctic sea extent has fluctuated in the past, why is its behaviour this year so worrying? Because, according to Doddridge and Purich, the current low sea-ice period could represent a new state for Antarctica. One in which warmer water temperatures prevent sea-ice coverage from returning to its previous state.
How did they come to this conclusion? By comparing ocean temperature measurements from 100 metres to 200 metres below the surface with sea ice measurements, the pair found that strong subsurface warming began in 2015 and explained substantial sea ice loss in certain regions the following year.
"Since then, the warm subsurface ocean seems to be maintaining the low sea-ice coverage," the pair say.
"Together, this evidence suggests the overall way of how Antarctic ice behaves in the atmosphere-ocean-sea ice system has changed. Our results suggest that even though the record-breaking low sea ice we’ve seen this year is shocking, it is likely to be the new abnormal."
Doddridge and Purich think they have uncovered preliminary evidence for the inevitable decline of Antarctic sea ice which climate models have long predicted. Craig Stevens, a professor in ocean physics at the University of Auckland, says the consequences will be felt far beyond the poles:
"These floating expanses of frozen seawater are central to how our world works. They regulate how much light our planet reflects, help ventilate the oceans, and host important ecosystems in the form of algal meadows on their underside."
Stevens explains that polar sea ice also connects the atmosphere with the ocean surface and deeper waters. Less sea ice means less cold, oxygenated seawater sinking to the abyss, where it drives deep water currents which redistribute heat throughout the global ocean.
This great ocean conveyor has been a significant brake on global heating so far. Estimates suggest more than 90% of the excess heat caused by burning fossil fuels and chopping down forests (among other activities which emit greenhouse gases like CO₂) has been absorbed by the ocean.
"The scale of the oceanic contribution to storing heat means any small change to how this has operated over the past millennia may have very large impacts," Stevens adds.
"It is impossible to overstate the urgency with which we need to reduce greenhouse gas emissions."
- Jack Marley, Environment commissioning editor
Was this email forwarded to you? Join the 20,000 people who get one email every week about the most important issue of our time. Subscribe to Imagine.
Devastatingly low Antarctic sea ice may be the ‘new abnormal’, study warns
Sea ice around Antarctica has always followed a predictable seasonal cycle. Now, we've experienced a sudden dramatic loss, and the changes are here to stay.
Read more
Record low Antarctic sea ice is another alarming sign the ocean’s role as climate regulator is changing
The world's oceans regulate our climate, but they are entering uncharted territory, with record surface warming and changes to Antarctica's deep meltwater which drives global currents.
Read more
Antarctica’s heart of ice has skipped a beat. Time to take our medicine
The rhythmic expansion and contraction of Antarctic sea ice is like a heartbeat. But there's been a skip in the beat. Deeply concerned scientists have released a diagnosis for policy-makers.
Read more
Antarctica is missing a chunk of sea ice bigger than Greenland – what’s going on?
Sea ice extent in July 2023 has been around 10% below last year's record low for the month.
Read more
I’ve spent 40 years studying Antarctica. The frozen continent has never needed our help more
After several decades in research, including 22 years at the Australian Antarctic Division, this scientist is standing up for our icy continent. Here's why Antarctic research needs ongoing funding.
Read more
Fractured foundations: how Antarctica’s ‘landfast’ ice is dwindling and why that’s bad news
More trouble in Antarctica: the extent of frozen seawater fastened to the coast (called landfast ice) hit a record low in March 2022. If this trend persists, the consequences could be catastrophic.
Read more
Latest from The Conversation on climate change
a.. Renewables are cheaper than ever yet fossil fuel use is still growing – here’s why
b.. What are ‘planetary boundaries’ and why should we care?
c.. Libya dam collapse: engineering expert raises questions about management
d.. How weather ‘blocks’ have triggered more extreme heatwaves and floods across Europe
The Conversation is an independent source of news and views, sourced from the academic and research community and delivered direct to the public.
You are receiving this email because you have signed up to Imagine, a weekly newsletter from The Conversation.
From: Imagine newsletter
Sent: Wednesday, September 20, 2023 9:02 PM
Subject: Has Antarctica entered a new state?
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.enwl.net.ru/pipermail/enwl-eng/attachments/20230921/f72ab74a/attachment-0001.html>
More information about the Enwl-eng
mailing list