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Book Review

Antarctica’s growing green space

Source: Lee, J. et al, Climate change drives expansion of Antarctic ice-free habitat, Nature, 2017, doi:10.1038/nature22996

Islands in the ice

When you imagine Antarctica, you probably think of ice. While most of the Antarctic continent is covered in ice, there are in fact some places, that are permanently ice-free. These ice-free regions tend to be small isolated patches of habitat surrounded by ice, similar to islands surrounded by ocean. They can be exposed mountaintops, cliff sides, coastal oases, or islands and can be as small as 1 km2 and as large as 1000 km2.

Less than 1% of Antarctica is permanently ice-free, but these areas support almost all of Antarctica’s land biodiversity, including many species of microbes, lichen, mosses and fungi. These patches of ice-free land are also important breeding grounds for seals and seabirds. Just like on an island, the geographic isolation of these habitats means that they tend to support many separate unique ecosystems, with many species confined to a single region, or even a single ice-free area.

 

Measuring the melt

Despite the large biodiversity supported by ice-free regions, scientists have paid little attention to how they are affected directly or indirectly by climate change. As the Earth warms, land ice covering Antarctica is melting in some regions, potentially expanding and changing the ice-free environment. There has been a large scientific effort to measure and understand how Antarctic ice has already changed and how it will continue to change in the future. Armed with this information, a group of scientists from Australia and the UK set out to determine how this will change Antarctica’s ice-free areas and what this means for the ecosystems that live there.

First, the scientists estimated how much Antarctic ice is expected to melt between 2014 and 2098. The amount of ice melt depends on how much warming occurs over the rest of the century as a result of greenhouse gas emissions, so that is highly dependent on how global emissions change in the future. To handle this, the researchers looked at two different emissions scenarios: in the first, we continue along a similar rate of increasing greenhouse gas emissions as we are now, with no efforts to reduce emissions; in the second, there is significant effort to reduce emissions later over the rest of the century. These two scenarios provide a lower and upper bound, and its most likely what happens in the real world will end up somewhere in between.

Figure 1 from Lee et al. 2017 showing the change in degree days, change in rainfall and thickness of ice melt in meters from 2014 to 2098 under the high emissions scenario.

Growing the green

The high emissions scenario predicts that by 2098, more than a 1 meter (3 foot) layer of ice will have melted along most of Antarctica’s coastlines and up to 7 meters along the Antarctic peninsula. This level of melt would lead to an increase of 25% in the total ice-free area in Antarctica. Along the Antarctic Peninsula, if we continue our trajectory of high emissions, this would cause the ice-free area to triple. However, even if we rapidly curb emissions, there will be a substantial increase in ice-free areas along the Antarctic Peninsula, although elsewhere in Antarctic will not experience much change. So, no matter what we do, there will be more ice-free areas in Antarctica at the end of the century. The more challenging question is: how will this affect ice-free species and ecosystems?

Figure 2 from Lee et al. 2017 showing the growth of ice-free areas by the end of the century.

Winners and losers

One of the most significant consequences of expanding ice-free area is that as the areas expand, many small isolated patches will grow and become connected. This will uncover potential new habitat for species and also make it easier for species to disperse to new regions. This would likely provide more resources and space for native species to thrive, and increase gene flow between populations. At the same time, the greater connections between ice-free regions could allow invasive species to spread, threatening the native species. In fact, already scientists have found that invasive grasses have colonized newly ice-free land in front of a retreating glacier. Clearly the ecosystem response to expanding ice-free habitats is complex, and scientists do not yet have enough information to determine which species will be winners and which will be losers.

This study clearly highlights the need for more research and monitoring of habitats and ecosystems in Antarctica’s ice-free areas, so that we can better predict how they will respond to the melting of ice on the Antarctic Peninsula expected over the next century. Armed with this science, conservationists can begin to tackle ways to preserve these unique and important ecosystems.

Figure 4 from Lee et al. 2017 showing a close up of ice free areas on the Antarctic peninsula currently in blue, with reduced emissions in orange and for the high emissions scenario in dark red.

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