How Ross Island tells the story of climate change in Antarcticaby Rebecca Priestley
News of summer heatwaves at home was sombrely received by scientists in Antarctica, where signs of climate change will have a global impact.
Near the colony, in small basins in the rock, are lakes rimmed with bright green or lurid orange algal mats. On either side of a small stream not much more than a trickle, tiny blobs of greeny-brown moss are rare evidence of terrestrial life.
It’s late January, and at Scott Base, TV news of a heatwave at home – in Invercargill it’s a record 32°C – is watched in sombre silence by scientists.
Much of the science supported by Antarctica New Zealand, the government agency responsible for science and environmental protection in Antarctica, is related to understanding past climates and assessing the likely effects of a warming ocean and atmosphere. The summer sunshine, trickling stream, colourful mosses and algae on Cape Royds now feel like ominous signs of things to come.
Daily weather observations, taken at Scott Base since 1957, show a slight overall warming trend but no more than might be expected from natural variability. A complex interaction between the gradually closing ozone hole and strong westerly winds seems, so far at least, to be maintaining the cold in high southern latitudes – Scott Base is at 77.8°S.
The Antarctic Peninsula, however, which extends as far north as 63°S, is one of the fastest-warming parts of the planet. Average temperatures have increased nearly 3°C in the past 50 years, resulting in several dramatic ice-shelf collapses. Progressive loss of sea ice has led to falling populations of krill and adélie penguins.
Air temperatures haven’t increased at Ross Island, but rising sea temperatures and erratic annual sea-ice behaviour are affecting the entire continent. A dramatic loss of sea ice in McMurdo Sound forced the New Zealand and American teams to cancel or scale down summer science projects because locations marked for campsites, instrument deployment or travel were now open water.
Regina Eisert, from the University of Canterbury’s Gateway Antarctica, was studying the Ross Sea (Type C) orca. Carrying biopsy guns and hydrophones and wearing bright orange immersion suits, Eisert and her team were flying out to the ice edge each night to study the killer whales that feed on Antarctic toothfish. She was concerned that loss of sea ice would “radically affect primary production in the Southern Ocean”.
Simple plants such as grasses form the base of the food chain in most terrestrial environments, but the Antarctic marine food chain is supported by algae that grow on the underside of the sea ice. These “upside-down meadows”, as Eisert calls them, are grazed by krill, which are eaten by the small fish, which are eaten by the bigger fish, and so on. Less sea ice means less algae, which may mean less food for every creature higher up the chain.
This season’s loss of sea ice in McMurdo Sound may or may not be part of a trend. The past two seasons have seen record minimum total sea ice around Antarctica, but some parts had more sea ice than usual. James Renwick, a professor of physical geography at Victoria University of Wellington, says the one clear climate-change signal in Antarctica “is the warming of the ocean at depth and under the ice shelves”.
The two research bases – Scott Base and McMurdo Station – and the historic huts on Ross Island are all on the coast; explorer Robert Falcon Scott’s hut at Cape Evans sits on a gravelly beach. Any sea-level rise may be expected to threaten the buildings at Ross Island, but Tim Naish, from Victoria’s Antarctic Research Centre, and director of the New Zealand SeaRise programme, says ice-sheet melt will actually cause the sea level at Scott Base to fall. Sea-level rise does not occur uniformly across the Earth’s surface, Naish says: masses such as a mountain range or an ice sheet exert a gravitational attraction.
“If you’ve taken water out of the ocean to grow an ice sheet, in the ocean nearby there will be a gravitational attraction pulling the ocean up towards the ice sheet.”
So, sea level around Antarctica is being pulled up by the massive ice sheets of West and East Antarctica. The opposite occurs when an ice sheet melts: the gravitational pull near the ice sheet weakens and the local sea level falls. Thus, if the main area of ice melt is Greenland, which is likely to be the case until the middle of this century, most of the sea-level rise will happen in the Southern Hemisphere; if melting of the West Antarctic Ice Sheet accelerates, then most of the sea-level rise will be in the Northern Hemisphere.
But if partial melting of the West Antarctic Ice Sheet contributes 1m of average global sea-level rise, then the sea level at Scott Base, which is close to the West Antarctic Ice Sheet, is predicted to drop by as much as 2.5m. This could happen within 100 years, according to some ice-sheet models. If the West Antarctic Ice Sheet completely melted, the local sea-level fall near Scott Base could be as much as 8m.
There’s broad scientific agreement that by the end of the century, the McMurdo Sound area, including Ross Island and the transantarctic mountains of South Victoria Land, will be warmer than at present, and there will be less sea ice, and loss of ice around the margins of Antarctica. “What will be happening with the Ross Ice Shelf, and the other ice shelves … will we see this irreversible melt kick in before the end of the century?” Renwick says. “Watch this space.”
More data needed
Our slice of Antarctica, known as the Ross Dependency, is starting to change but we still need more data – about the marine environment, the ice-ocean-atmosphere interactions, paleoclimates – so we can monitor, measure and project future changes. How much these changes will affect the rest of the planet will depend on what we do over the next few years.
Recent research, including by members of the New Zealand Antarctic Research Centre, suggests that if we can limit global warming to no more than 2°C above pre-industrial levels, there’s a chance we can save the Antarctic ice sheets and protect the world from catastrophic sea-level rise. But present commitments to greenhouse-gas reduction will see warming of more than 3°C by 2100. We need to do more, and we need to do it now.
This article was first published in the May 19, 2018 issue of the New Zealand Listener.
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