18.9 C
Toronto
Sunday, May 19, 2024

Subscribe

Antarctic warming alters atmosphere, ice shelves, ocean & animals

The climate is changing, and many species endemic to Antarctica are at risk. Image by Rod Long via Unsplash.
  • The world’s latest record-high temperatures are increasingly putting Antarctica’s role in regulating global climate and ocean currents at risk. But so far, most signs indicate that the continent has not yet reached a point of no return. A rapid reduction in fossil fuel extraction and carbon emissions could still prevent the worst outcomes.
  • Increased persistence of the Antarctic ozone hole over the past three years could be an indication of climate change, as it cools the south polar stratosphere, though high variability in this phenomenon and its complexity make causality difficult to prove.
  • As global warming continues to melt Antarctica’s edges, a modeling study shows that fresh water going into the ocean could result in the next three decades in a more than 40% slowdown in the currents carrying heat and nutrients northward, essential to sustain ocean life as we know it. If ice shelves melt, allowing Antarctica’s ice sheets to flow to the sea, sea level rise will escalate.
  • The latest discovery of a new colony of emperor penguins (Aptenodytes forsteri) in a marginal habitat of the Antarctic is good news, but also bad news, as it further highlights the vulnerability of the species as Antarctic ice masses destabilize — volatility that threatens their survival.

The climate is changing fast, with even Earth’s most remote areas unable to dodge the bullet. This includes Antarctica — a region that has long seemed behind the curve when it comes to warming. But how radically or fast the south polar region’s atmosphere, oceans, ice and land will alter is hard to say.

In January, data compiled by the World Meteorological Organization revealed the last eight years as the hottest on record globally. On the Antarctic Plateau, the coldest place on the planet, the Concordia Research station hit its highest temperature reading ever in early 2022 at -12.2 degrees Celsius (10.04 degrees Fahrenheit), while Antarctic sea ice shrank the same year to its smallest extent since recordkeeping began, to 1.92 million square kilometers (741,000 square miles). That’s an alarming record — but 2023 beat it, at 1.79 million km2 (691,000 mi2).

This is potentially bad news for humanity: The White Continent, which holds 90% of the world’s ice, plays a crucial role in regulating Earth’s climate. In an email to Mongabay, the British Antarctic Survey (BAS) underlined the “disproportionate” influence the poles have on climate, stressing the contrast between the reflective properties of large white, ice-covered areas (which send the sun’s heat back into space) and the surrounding dark sea surface (which absorbs the sun’s heat, adding to global warming).

The big question facing researchers now is whether or not Antarctica is showing signs of hitting an irreversible tipping point.

When asked that question by Mongabay, Matthew England, scientia professor at the University of New South Wales (UNSW), responded that Antarctic records will keep getting broken for a while to come. “But the extent to which they are broken will be set by our future emissions pathways.” Put simply, humanity, though on thin ice, still has time to change course — but no one knows precisely how much.

Layer over the sea.
Chemicals once used in aerosol sprays and refrigerants are called chlorofluorocarbons, or CFCs. Their accumulation in the atmosphere led to the Antarctic ozone hole that was discovered in the late 1980s, leading to the Montreal Protocol to ban new production and use of CFCs. Image by Rod Long via Unsplash.
Graph of Atmospheric ozone mixing ratios for 2022 over the South Pole. Note the large ozone spike above 18 kilometers (11 miles) altitude from September to December.
Atmospheric ozone mixing ratios for 2022 over the South Pole. Note the large ozone spike above 18 kilometers (11 miles) altitude from September to December. Graph by the Earth System Research Laboratories’ (ESRL) Global Monitoring Laboratory (GML) of the National Oceanic and Atmospheric Administration (NOAA).

Ozone hole persistence: Atmospheric variability or climate trend?

The large ozone hole that currently appears annually over the Antarctic was mostly human-caused — the product of the build-up of manufactured ozone-depleting chemicals in Earth’s atmosphere during the 20th century. The landmark Montreal Protocol agreement of 1987 significantly diminished the size of the hole, reducing the risk of the ozone shield’s collapse and of the many cancers that would have ensued due to direct exposure to ultraviolet radiation from the sun.

Scientists flagged a potential new trend in 2022, when the ozone hole took longer than usual to close for the third consecutive year — annual persistence never seen in the previous 40 years that the Copernicus Atmosphere Monitoring Service (CAMS) has been taking measurements.

The Antarctic ozone hole begins enlarging in August, reaches its maximum size in late September, then usually declines in October and closes in November. But for three years now, the hole has remained larger than typical throughout November, with closing not occurring until late December — all three years also set a record for the slowest warming trends of the stratosphere over Antarctica, which makes climate change suspect as a possible cause of the late ozone hole closing.

The size of the ozone hole ranked 10th largest in 2020, eighth in 2021, and 12th in 2022. Thanks to the Montreal Protocol — which instituted a phaseout of most manufactured ozone-depleting chemicals, scientists now anticipate that the Antarctic ozone layer will recover to 1980 values by around 2066.

“With chlorine and bromine in the stratosphere back at their natural levels or almost … we can be confident that ozone holes will disappear as the ‘chemical fuel’ behind ozone destruction will have been eliminated — for good,” according to Vincent-Henri Peuch, head of the CAMS.

To Peuch, a question for future research, is whether recent ozone hole persistence might become a trend. He writes: “The last three years have been marked by strong vortices [powerful high-altitude winds that circle the Antarctic region] and low [stratospheric] temperatures, which has led to consecutive large and long-lasting ozone hole episodes. There is a possible connection with climate change, which tends to cool the stratosphere. It is quite unexpected though to see three unusual ozone holes in a row. It is certainly something to look into further.”

However, Peuch said he believed it was “quite unlikely” that 2023 would follow the same pattern.

“Although stratospheric cooling associated with greenhouse gas increases could be playing a role in preventing the ozone hole from healing, it will be difficult to ‘prove this connection’ using data alone,” Ramalingam Saravanan, head of the Department of Atmospheric Sciences at Texas A&M University, wrote in an email. “This could occur purely by chance and is unlikely to be the indication of a tipping point.”

An ice shelf.
Antarctica has shed around 149 billion metric tons of ice per year between 2002 and 2020, according to NASA data. The melting of floating ice shelves appears to be freshening seawater and slowing the Southern Ocean overturning circulation, which could greatly impact nutrient supplies to the world’s marine life. Image by 66 north via Unsplash.

Abyssal ocean warming and overturning slowdown driven by the Antarctic melt. Video by Matthew England. Download File: https://imgs.mongabay.com/wp-content/uploads/sites/20/2023/06/12131952/4.mp4?_=1

Melting Antarctic ice to impact world’s oceans?

Signs of a warming Antarctic climate are especially worrying as melting ice shelves impact Earth’s oceans. A modeling study published in March by Australian scientists in Nature found that the Southern Ocean overturning circulation — a network of strong ocean currents driven by deep Antarctic waters that carry heat, carbon, oxygen and nutrients crucial to ocean life northward — could slow by more than 40% by 2050 under a high-emissions scenario. More recent research conducted by some of the same scientists and released in Nature Climate Change suggested the Southern Ocean overturning circulation had ebbed by 30% since the 1990s.

The cause appears to be Antarctica’s melting edges, which, due to climate change, are adding greater volumes of fresh water to the Southern Ocean, lowering the density of about 250 trillion metric tons of salty surface water each year, which reduces its ability to sink and drive the deepest flows that spread nutrients to the world’s other ocean basins.

“If our model simulations turn out to be correct, it is difficult to see the Antarctic overturning circulation surviving beyond 2100,” said UNSW’s England, who co-authored both studies. Given the amount of meltwater observed at just over 1 degree Celsius (1.8 degrees Fahrenheit) of warming planetwide, he suggested that a collapse of the currents would be “highly likely” above 2 degrees Celsius (3.6 degrees Fahrenheit) of warming over preindustrial levels.

Scientists expect average global temperatures to increase in the next five years, temporarily rising about 1.5 degrees Celsius (2.7 degrees Fahrenheit) — fueled by global warming and a powerful El Niño event now gathering strength in the eastern Pacific Ocean. The 2 degrees Celsius threshold could be reached by as early as 2050, according to a dire warning just issued by climate scientist James Hansen, though most researchers say that point will more likely come later this century if humanity doesn’t drastically curb emissions.

But that’s not the only peril originating at the Antarctic’s melting margins. “The biggest threat to [the] Antarctic ice sheet … leading to sea-level rise is warmer water getting beneath the [floating] ice shelves and thinning them,” according to Richard Alley, geosciences professor at Pennsylvania State University. Ice shelves surrounding Antarctica (whose melting doesn’t add to sea level) act like a cork in a bottle, holding back ice sheets on land from flowing into the sea and greatly increasing sea level.

“All of the ice shelves now are generating friction with their sides or with local seafloor highs that they scrape across. [But] ice-shelf loss removes that friction and allows non-floating ice [in the ice sheet] to flow more rapidly into the ocean, raising sea level,” he wrote to Mongabay.

“Global warming that has already happened certainly commits us to further sea-level rise,” BAS marine geophysicist Robert Larter explained in an email, as oceans and ice sheets will take a long time to reach equilibrium.

He however stressed that all was not lost: “Records in ice cores and marine sediment cores from the last interglacial period 125,000 years ago, when average global temperatures rose gradually to a maximum that was still a little warmer than today, provide some reassurance that we have probably not yet reached a point of no return.”

Under the business-as-usual greenhouse gas emissions scenario, 80% of the colonies of emperor penguins (Aptenodytes forsteri) could be quasi-extinct by 2100. Image by Dylan Shaw via Unsplash.
Map of Antarctic melting.
In February, Antarctic sea ice extent set a new record low, putting at risk the species that depend on stable sea ice as a breeding habitat. NASA Earth Observatory images by Lauren Dauphin, using data from the National Snow and Ice Data Center (NSIDC).

Globally warmed plight of emperor penguins

Climate change has also come hard ashore in Antarctica. In January, BAS scientists discovered a new colony of emperor penguins (Aptenodytes forsteri) in West Antarctica, raising the number of known colonies on the Antarctic coastline to 66 in total. Great news? Not exactly.

Typically found in remote and often inaccessible areas, the species, endemic to Antarctica, depends on bitterly cold temperatures and stable sea ice as a breeding habitat, with chicks fledging in December or January.

Among breeding locations, they mostly target the windward side of bays, headlands, glacier tongues and ice shelves, BAS researchers wrote in a 2020 study, in which they reported 11 colonies located in regions that weren’t identified as “possible climate refugia,” suggesting population declines could be greater than anticipated in these colonies as warming escalates.

Emperor penguins are particularly vulnerable to the loss of sea ice, rising temperatures and altered wind regimes; and the newly found colony is no exception: Not only is it small — home to just 500 birds, which could be detrimental to its persistence and survival — but it is also located in an area badly affected by recent sea ice loss.

“If we find more colonies in more marginal habitat, it means that a greater percentage of the population is likely to be affected by sea ice loss in the future,” BAS geospatial scientist and cartographer Peter Fretwell stressed in an email to Mongabay. “[T]he more recently found colonies are all in this category.”

A 2019 study projected that under business-as-usual greenhouse gas emissions, 80% of the emperor penguin colonies could be quasi-extinct by 2100. But if the world were to cap temperatures rises at 1.5 degrees Celsius, this would include just 19-31% of them.

“Monitoring the future of these colonies … will be part of counting the cost of climate change,” Fretwell said.

The species, currently listed as “near threatened” on the IUCN Red List, points to the vulnerability of ice-dependent animals even before extreme warming has occurred.

A scene from the Antarctic, boat in the sea.
Antarctica is one of the toughest regions to undertake field research, but new tools like robotics, artificial intelligence and high-quality remote sensing technology are helping gather more data and improve modeling. Image by Dylan Shaw via Unsplash.

Antarctica tomorrow

Antarctica’s geographic isolation and extreme climate have historically spared it from most of the environmental threats that the rest of the world endures — but human-induced warming coming from afar is now overturning this protected status.

“Whether this is a large problem soon, or whether we have a cushion before the warming and other changes become large enough to be dangerous, remains deeply uncertain,” Alley said. “Many of us believe that the pace of research is at once hugely impressive … but not nearly fast enough to provide the guidance to policymakers that would with confidence allow them to make appropriate decisions well before we might approach an [Antarctic] tipping point.”

Being one of the toughest regions to undertake field research, Antarctic data is not as complete or robust as for its northern counterpart, but the BAS is optimistic about future research due to “a shift in the way Antarctic science happens,” especially incorporating new useful tools to improve modeling.

“There are grounds for cautious optimism that the worst consequences can be avoided,” Larter concluded, with politicians moving from debating the reliability of scientific results to deciding what should be done. But national carbon reduction pledges fall “far short” of the urgency, he conceded.

One thing is crystal clear: Already identified Antarctic climate change trends could, if they escalate, have huge consequences for far distant ecosystems and human communities. As with the northern polar region, what happens in Antarctica does not stay in Antarctica.

Citations:

Copernicus: Unusually persistent Antarctic ozone holes in 2020-2022. (2022). Copernicus Atmosphere Monitoring Service. Retrieved from https://atmosphere.copernicus.eu/copernicus-unusually-persistent-antarctic-ozone-holes-2020-2022

Li, Q., England, M. H., Hogg, A. M. et al (2023). Abyssal ocean overturning slowdown and warming driven by Antarctic meltwater. Nature 615, 841–847. doi:10.1038/s41586-023-05762-w

Gunn, K. L., Rintoul, S. R., England, M. H., Bowen, M. M. (2023). Recent reduced abyssal overturning and ventilation in the Australian Antarctic Basin (2023). Nature Climate Change. doi:10.1038/s41558-023-01667-8

New emperor penguin colony discovered (2023). British Antarctic survey. Retrieved from https://www.bas.ac.uk/media-post/new-emperor-penguin-colony-discovered/

Fretwell, P. T., Trathan, P. N. (2020). Discovery of new colonies by Sentinel2 reveals good and bad news for emperor penguins. Remote Sensing in Ecology and Conservation, Volume 7, Issue 2, pp. 139-153. doi:10.1002/rse2.176

Jenouvrier, S., Holland, M., Iles, D., Labrousse, S., Landrum, L., Garnier, J., Caswell, H., Weimerskirch, H., LaRue, M., Ji, R., Barbraud, C., (2019). The Paris Agreement objectives will likely halt future declines of emperor penguins. Global Change Biology, Volume 26, Issue 3, pp. 1170-1184. doi:10.1111/gcb.14864

Juliette Portala
Juliette Portala
Juliette Portala spent some years in Poland looking into fossil fuel players for Reuters – keep your enemies closer, they say! She is now looking to confront the lack of climate news coverage as a freelance reporter, finding her own way between storytelling and activism.
Subscribe
Notify of
guest

0 Comments
Inline Feedbacks
View all comments

Latest Articles

0
Would love your thoughts, please comment.x
()
x