Choosing the future of Antarctica

In a new article in the journal Nature, Stephen Rintoul and colleagues present two very different visions of Antarctica’s future, from the perspective of an observer looking back from 2070. In one vision, humanity continues to exploit Earth’s natural resources (such as fossils fuels) and does little to protect the environment, and in the other, there is a global movement towards conservation. The article shows how Antarctica will change over the next 50 years, should either of these two situations occur.

Post by Jacob Bendle.

Two visions of Antarctica’s future

Vision 1 looks back from a future in which fossil fuel usage and greenhouse gas emissions continued to rise rapidly, and where little action was taken to protect Antarctica from major changes.

Vision 2 looks back from a future in which the rise in greenhouse gas emissions is reduced, and where strong action was put in place to protect Antarctica from major change.

How do the authors predict how Antarctica will change in the future?

The visions described above are not fact, but hypothetical ‘best’ and ‘worst’ cases. However, Rintoul and colleagues are able to estimate what the impacts of future greenhouse gas emissions might be using the findings of climate and ice sheet simulations, and using records of past environmental change.

Rintoul and colleagues use the predictions stated in the IPCC climate report, which brings together the work of hundreds of scientists involved in studying past, present, and future changes in Antarctica.

How will Antarctica change under high greenhouse emissions?

Under the IPCC’s high greenhouse gas emissions scenario, Antarctica will change dramatically by 2070. The major changes are shown in the figure below.

Summary of the impacts on Antarctica and the Southern Ocean in 2070, under a ‘high emissions’ scenario. Reprinted by permission from Nature [‘Choosing the future of Antarctica’; S. Rintoul and colleagues] [Copyright 2018].

Warmer air temperatures

The air temperature over Antarctica will be 3°C warmer by 2070. This will cause summer ice-melt in low-lying coastal areas, and will contribute to destabilising ice shelves.

The Southern Ocean warms and ice shelves retreat

The westerly winds that blow around the mid-latitudes will move south and become stronger by 2045. This will bring warm subtropical water into the Southern Ocean, which can enter beneath floating ice shelves and cause basal melting, thinning and retreat. This will cause some ice shelves (such as those on the Antarctic Peninsula) to disappear completely, and the volume of ice shelves to reduce by 23% by 2070.

Ice sheet losses and sea level rise

Ice shelves are important because they hold back the glaciers that feed into them. Their retreat will, therefore, allow glaciers to flow more rapidly into the sea, where they will contribute to sea-level rise.

In West Antarctica, the retreat of grounding lines will cause ice streams to accelerate and ‘marine ice sheet instability’ to occur. This change will be irreversible, and by 2070 the Antarctic Ice Sheet will have contributed 27 cm to global sea level.

Ecosystems are damaged

As greenhouse gas emissions rise, the Southern Ocean will become more acidic, and calcium carbonate minerals (such as aragonite) that make up the shells and skeletons of some marine creatures will dissolve. This will have a negative impact on Southern Ocean food webs.

Shipping access will become easier due to reduced sea ice extent in summer (43%) and winter (40%), which leads to more fishing and depleted fish and krill stocks. Due to reduced prey, some penguin populations will also decline.

Invasive species

As glaciers recede and more of the Antarctic continent becomes ice free, foreign plants and animals are able to colonise it. Some of these result from greater human presence (e.g. fishing, mining) in Antarctica, and will alter natural biodiversity.

Can Antarctica be protected from major change?

But what if greenhouse gas emissions are lowered by 2070, and governments worldwide act to protect the environment? Rintoul and colleagues also describe a best-case scenario, which is compared to the high emission situation in the figure shown below.

A comparison of Antarctica and the Southern Ocean under ‘low emissions’ [left] and ‘high emissions’ [right]. Reprinted by permission from Nature [‘Choosing the future of Antarctica’; S. Rintoul and colleagues] [Copyright 2018].

Stable surface air-temperature

The air temperature over Antarctica will rise by 1°C (rather than 3°C) by 2070, reducing the amount of melting at the surface of glaciers and ice shelves.

Stable Southern Ocean temperature

The westerly winds will not shift southwards, and will even gradually move toward the equator. This reduces the amount of warm subtropical water entering the Southern Ocean, and limits the loss of ice shelves to just 8%.

Ice sheet losses and sea level rise slow down

Stable ice shelves will continue to prevent glaciers flowing into the sea. While some glacier retreat and thinning occurs, the marine-based ice sheet in West Antarctica does not completely disintegrate, which allows rapidly retreating glaciers to re-stabilise, and limits Antarctic sea level contributions to just 6 cm by 2070.

Biodiversity maintained

Reduced CO2 emissions will cause Southern Ocean acidification rates to stabilise by 2040, and limit the decline of marine creatures with calcium carbonate skeletons. Also, sea ice losses of 12% (rather than 43%) will help to preserve seabird and seal populations. On land, the continued presence of glaciers prevent the invasion of foreign plant species.

Responsible management from governments worldwide

To further protect Antarctica and the Southern Ocean, Rintoul and colleagues highlight the importance of strict regulations on human activities (e.g. fishing, mining, tourism) and presence in Antarctica.

They suggest that international collaboration and good relationships between key organisations (such as the Antarctic Treaty System and the United Nations) will be vital to minimising negative changes.

Why the article is important

To summarise, in this article Rintoul and colleagues use a unique, effective, and engaging method of communicating the importance of future climate change in Antarctica.

Firstly, the article demonstrates just how wide-ranging future Antarctic changes could be, across all systems (e.g. cryosphere, biosphere) that make up the physical environment.

Secondly, it highlights how changes in any one system could have knock-on effects in others. For example, ice shelf retreat will cause rapid glacier loss to the oceans [and sea level rise] and, in turn, glacier loss will allow invasive plants to colonise newly uncovered terrain, and alter natural biodiversity.

Finally, and most importantly, by presenting two starkly different, but believable visions, the article provides an excellent starting point for scientists, politicians, and the general public to discuss Antarctica’s future, and consider how to tackle (or not!) the ongoing changes in the southern high-latitudes.

References

Rintoul, S.R., Chown, S.L., DeConto, R.M., England, M.H., Fricker, H.A., Masson-Delmotte, V., Naish, T.R., Siegert, M.J. & Xavier, J.C. 2018. Choosing the future of Antarctica. Nature, 558, 233-241.

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This entry was posted in Climate Change, New Papers, Sea level rise and tagged , , , by Jacob Bendle. Bookmark the permalink.

About Jacob Bendle

I am a Quaternary geologist with a focus on palaeo-ice sheet dynamics and palaeoclimate change during the last 20,000 years. I study glacial landforms to reconstruct glacier (and glacial lake) extents, dimensions and depositional processes. However, my main focus lies with the sedimentological analysis of annually-layered glacial lake sediments (known as varves) to develop continuous, high-resolution records of past ice sheet response to sub-centennial (rapid) climate shifts. Read more about me at http://www.antarcticglaciers.org/about-2/jacob-bendle/

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