Gareth Morgan and Geoff Simmons: High risk shift in vital chiller ocean

Yesterday, we looked at how the race for resources is heating up in the Antarctic. That's not the only thing getting hotter. In our 2009 book Poles Apart, written with John McCrystal, we surveyed the evidence for global warming. The balance of evidence points to warming as a result of burning fossil fuels.

To our far south lies Antarctica, a laboratory made in heaven for the study of climate change. The relatively untouched, icy environment is perfect for researching how the climate has changed in the past, as well as measuring the pace of change now under way. Nowhere on Earth is as sensitive to climate change as the polar regions.

Climate change deniers have enjoyed pointing out that, unlike the Arctic, Antarctica has not warmed much overall. Average temperatures across the continent haven't really budged as yet, and in some areas like our own Ross Sea the extent of sea ice is actually increasing.

Ironically this increasing ice cover may even prevent our voyage from reaching our ultimate destination, Scott Base. However, these averages mask the reality of rapid change, change that sees the Antarctic Peninsula warming almost as fast as the Arctic, while up at the high altitudes of the South Pole the temperature track is one of cooling.

In the last five decades, the peninsula has warmed at a rate of 2.5C per century, the Ross Ice Shelf area at a more modest 1C per century, and the pole itself shows no change.

The Southern Ocean is also warming, freshening (a sign of ice melting) and acidifying (as a result of absorbing more carbon dioxide) faster than any ocean in the world. These signals can be seen up to a depth of 1km in the ocean.

There are reasons why Antarctica overall might not be warming as quickly as the Arctic. Incredibly, the hole in the ozone layer actually has a cooling influence as ozone is a greenhouse gas (albeit a pretty useful one for those of us not keen on being blitzed by the sun's ultraviolet rays). Antarctica also has a "moat" of water around it, and without any land in the way the westerly wind whips the Southern Ocean into a swift current which insulates Antarctica.

This Antarctic Circumpolar Current acts a bit like a fleet of yachts circulating the start buoy of a harbour race waiting for the gun but meanwhile whipping up a current on a grand scale. It is a flow of superlatives; at 24,000km it's the longest and only major flow to connect the major oceans; and it soaks up about 70 per cent of the wind energy falling on the global ocean surface.

These two factors have spared Antarctica for now, but most climate change models predict the rapid warming trends of the Antarctic Peninsula will spread south. As is evident in the Arctic, global warming is likely to result in more rapid change in polar regions than elsewhere.

Part of what has always kept the polar regions so cool is the albedo effect - the cooling caused by ice reflecting sunlight back into space. As the ice melts from the warmer water lapping up against it, this cooling bonus will be lost. The seawater left behind after the ice melts absorbs more light than the ice previously did, which accelerates warming further.

Accordingly, the polar regions are expected to warm more rapidly than the rest of the planet, and this is what makes them such a rich laboratory for scientists monitoring the change.

What can we expect from climate change in the future? In short, we'll start to see more dramatic changes in Antarctica as the hole in the ozone layer repairs itself over time.

Projections are for the sea ice to retreat by 30 per cent this century. The upper layers of the Southern Ocean are expected to become fresher as the ice melts and winds will probably pick up over the Southern Ocean, which could boost the Antarctic Circumpolar Current as a result.

Changes in our Far South will have implications for New Zealand. As the westerly winds move south we'll have more settled weather, punctuated by more violent storms. But the biggest change we face will be the rising sea level. Levels are rising by over 3mm per year now, and predictions for the next round of the Intergovernmental Panel of Climate Change are likely to be bumped up to a 1m sea level rise this century. Doesn't sound like much here, but it will create plenty of climate change refugees.

More concerning is that our actions today are locking in much bigger changes over time. We know from our scientific endeavours in Antarctica the last time carbon dioxide levels in the atmosphere got to current levels, temperatures eventually rose an average of 2C to 3C. Over time, this was enough to collapse the West Antarctic Ice Shelf.

In combination with loss of the Greenland ice cap and the expansion of seawater as it warmed up, this raised sea levels by 15m to 20m. That was 120,000 years ago.

These sorts of changes are relatively easy to predict, but we have no idea of the knock-on consequences. Processes like the Antarctic Circumpolar Current and the freeze/thaw cycle of sea ice in Antarctica influence the world's climate and oceans. For example, the Southern Ocean drives the mixing of the world's oceans, which is vital for bringing nutrients back to the surface where plankton can use them to grow.

Under climate change, there will be changes to both the wind and ice in the Southern Ocean. The implications for ocean mixing and photosynthesis are unclear - we just don't know enough about how the ocean works. The stakes are high though because, ultimately, these processes determine the amount of life in the ocean.

We also don't understand how the rapid pace of warming might alter things. Our observations of previous warm periods have been from gradual natural processes, not sudden artificial increases in carbon dioxide levels.

The best example of this is in ocean acidification. In the past, changes in atmospheric carbon dioxide happened slowly, so the ocean had time to adjust to the change in acidity by accessing deep-water carbonate stores. In the laboratory, we know acidification affects any sea life with a shell, from shellfish to the myriad of tiny organisms at the bottom of the ocean food chain. But outside the lab we have no idea what the impact will be, because the world hasn't seen such a rapid change in ocean acidity in 20 million years.

Climatic changes, combined with the environmental impacts of humankind's accelerating race for resources down there, will impact the wildlife of our far south.

We'll explore the prospects for biodiversity in tomorrow's article.

ON THE WEB

Follow the project online at www.ourfarsouth.org.

Dr Gareth Morgan is an economist, portfolio investor, author and philanthropist. Economist Geoff Simmons is a researcher with the Morgan Foundation.