August 10, 2022

As Temperatures Rise, Antarctica is Turning Green

As Temperatures Rise, Antarctica is Turning Green
As Temperatures Rise, Antarctica is Turning GreenAs Temperatures Rise, Antarctica is Turning Green

The global climate is warming, and Earth’s polar regions are feeling the effects. A new study of the South Orkney Islands shows that the region has warmed significantly since the 1950s. The rise in warming in the South Orkneys exceeds the overall global warming.

As the islands warm, plant life is spreading.

The South Orkney Islands lie about 600 km (375 miles) northeast of the Antarctica Peninsula’s tip. Britain and Argentina both lay claim to the group of islands. Both nations maintain research stations in the South Orkneys: Argentina has one on Laurie Island and Britain has one on Signy Island.

A study based on Signy Island data going back to the 1950s shows that the climate is warming and that the spread of vascular plants in the warming conditions is turning more of the island green, especially since 2009. The study is “Acceleration of climate warming and plant dynamics in Antarctica,” published in the journal Current Biology. The lead author is Nicoletta Cannone from the Università degli Studi dell’Insubria, Dip. Scienza e Alta Tecnologia, Italy.

While the South Orkneys are separated from Antarctica by about 600 km, they’re still in a polar climate. About 90% of the islands were glaciated as of 2009, and the summers are very short and very cold. Ice-covered seas surround the South Orkneys seas from late April to November.

But the new study shows that things are changing in these remote islands. According to the paper, the two species of vascular plants on Signy Island responded to the climate change acceleration with a “striking advance,” according to the report.

“This is the first evidence in Antarctica for accelerated ecosystem responses to climate warming, confirming similar observations in the Northern Hemisphere.”

From “Acceleration of climate warming and plant dynamics in Antarctica” by Cannone et al. 2022

The warming hasn’t been a continuous trend. There was one period of pronounced cooling in the years since the study began. The study points out that “… a short but intense cooling occurred from the Antarctic Peninsula to the South Orkney Islands…” between 1999 and 2016.

But air temperature warming resumed in 2012 on Signy Island, accelerating the expansion of the two vascular plant species. “We also hypothesize that the “pulse” climatic event of the strong air cooling detected in 2012 did not appear to influence the vegetation community dynamics on this island,” the authors write. “The lack of negative impacts of the strong pulse cooling event in 2012 on both species could be explained by their ability to perform photosynthesis at low ambient temperatures.”

This figure from the study shows the Summer Air Temperature at Signy Island. Blue dots are SAT between 1960 and 2011, and orange dots are SAT between 2012 and 2018. Image Credit: Cannone et al. 2022.

Other research shows that the same type of accelerated ecosystem responses from climate warming occurs in the Arctic. A 2018 research article reported that plants are increasing their northern range in the Arctic and getting taller. A 2020 paper showed that the warming climate creates terrestrial algae blooms in Antarctica. But the authors of this paper say theirs is the first research to document the advance of vascular plants in the Antarctic. They also say that ongoing climate change will significantly affect the region.

“This is the first evidence in Antarctica for accelerated ecosystem responses to climate warming, confirming similar observations in the Northern Hemisphere,” they explain in their paper. “Our findings support the hypothesis that future warming will trigger significant changes in these fragile Antarctic ecosystems.”

There are two species of vascular plants native to Signy Island. One is D. antarctica, a flowering plant known as Antarctic Hair Grass. The other is C. quitensis, another flowering plant that’s also called Antarctic Pearlwort.

This figure from the study shows how climate warming resumed at Signy Island after the 2012 cooling and accelerated the expansion of D. antarctica and C. quitensis. D1 through D5 represent plant sites of increasing density. D1 is the least dense site and D5 is the densest site. Image Credit: Cannone et al. 2022.
This figure from the study shows how climate warming resumed at Signy Island after the 2012 cooling and accelerated the expansion of D. antarctica and C. quitensis. D1 through D5 represent plant sites of increasing density. D1 is the least dense site, and D5 is the densest site. Image Credit: Cannone et al. 2022.

“In the almost six decades up to 2018, D. antarctica exhibited a very large increase in the number of sites of occurrence, which doubled between 1960 and 2009 and then again between 2009 and 2018,” the authors write. C. quitensis expanded even more. “Colobanthus quitensis also showed a large expansion, even more so than D. antarctica in the last decade, involving both the number of sites of occurrence and their extent…” the paper says.

The number of sites with D. antarctica doubled between 1960 and 2009. Then it doubled again between 2009 and 2018. C. quitensis expanded even more than D. antarctica in the last decade.

This figure from the study illustrates the spread of both vascular plants native to Signy Island going back to 1960. The top row is D. antarctica and the bottom row is C. quitensis. From the paper:
This figure from the study illustrates the spread of both vascular plants native to Signy Island going back to 1960. The top row is D. antarctica, and the bottom row is C. quitensis. From the paper: “Distribution of D. antarctica and C. quitensis in 1960 (yellow dots) (A and D), 2009 (B and E), and 2018 (C and F) (green and magenta dots) in relation with the patterns of Holocene deglaciation and glacier boundaries and indicating the occurrence (magenta dots) or absence (green dots) of marine vertebrate disturbance in 2009 and 2018. Legend: dark blue, glacier boundaries as recorded in 2016; blue, glacier boundaries during the Little Ice Age; pale blue, terrains deglaciated between 6600 years BP and the Little Ice Age; white, terrains deglaciated before 6600 years BP.” Image Credit: Cannone et al. 2022.

The warming climate isn’t the only factor in this study. The image above shows areas of marine vertebrate disturbance. That refers to fur seals that inhabit the island. “In the last decade, the impact of fur seal disturbance on both species decreased, becoming almost negligible,” the authors explain. “During the last decade, both species expanded in response to air temperature warming and release from the limitation of animal disturbance.”

Climate change doubters might think they’ve found ammunition here. Some people might want to emphasize the reduction in animal disturbance as a factor in plant spread and downplay the effect of climate warming. The researchers don’t discount reduced animal disturbance, but it’s a secondary factor. “We also hypothesize that the accelerated population expansion of D. antarctica and C. quitensis could result from a combination of climate warming and the recently reduced impacts of animal disturbance. This hypothesis is compatible with observations in the Northern Hemisphere, in particular in Europe, where land-use change correlates with vegetation change but, as here, the primary driver of these responses was climate warming,” they write.

These are the two vascular plants native to Signy Island. On the left is D. antarctica and on the right is C. quitensis. Image Credit: L: By Lomvi2 - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=10372682. Image Credit: R: By Liam Quinn - Flickr: Antarctic Pearlwort, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=15525940
These are the two vascular plants native to Signy Island. On the left is D. antarctica and on the right is C. quitensis. Image Credit: L: By Lomvi2 – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=10372682. Image Credit: R: By Liam Quinn – Flickr: Antarctic Pearlwort, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=15525940

What does increased native planet growth due to a warming climate mean for the future of the Antarctic? On the surface of it, there could be some benefits. Increased plant growth removes more CO2 from the atmosphere through photosynthesis. “Such climate warming may benefit some and possibly many native Antarctic terrestrial species and communities in isolation…” the researchers write in their paper’s summary.

But it’s not just native plants that will benefit. They’ve exploited their cold niche for a long time, and other plant species haven’t gained a foothold on Signy Island. That could change, and the change could be disruptive.

Climate warming “… will also lead to increased risks from non-native species establishment. These may outcompete native species and trigger irreversible biodiversity loss and changes to these fragile and unique ecosystems,” they say in conclusion.

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