Antarctic penguin colonies threatened by changing climate
Researchers predict serious consequences for large Antarctic penguin colonies as the climate changes. In just a few decades, ice needed for nesting and feeding will be unavailable. Joellen Russell explains the changes in train as winds and ocean currents move, as air temperatures swing, at times hotter, at other times colder and as ocean chemistry changes from an equilibrium position which has allowed life to flourish.
Joellen Russell: It's an enormous current that you can basically see from space that separates the very warm waters of the subtropics from the polar waters around Antarctica. The current reaches from the surface down to 5,000 metres all the way to the bottom. It's so strong that it actually scours the bottom where it is constrained by topography. The current itself is driven by the westerly winds around Antarctica which are 30% stronger than the westerlies in the northern hemisphere. So these enormous winds drive this enormous current which basically communicates the deep water with the surface. The winds push the water away from Antarctica, all the way around Antarctica.
Robyn Williams: Professor Joellen Russell who is a geoscientist at the University of Arizona, and she is talking about forces four times more powerful than the Gulf Stream. It's affecting both rains and temperature in southern Australia in ways not seen in recent times. She is with Alexandra de Blas.
Joellen Russell: They push the water away in the surface layer, and since you can't have a hole in the ocean, the water has to up-well, and it up-wells from two to three kilometres down, the water comes up, up, up to the surface. It's amazing. So basically the Southern Ocean is the window between the surface and the deep ocean and the only place in the global ocean where waters up-well from that deep. It's unique in all the world, a geologic feature of immense importance to climate.
Alexandra de Blas: Okay, so this is really important in terms of diffusing some of the global warming that is occurring. The westerlies are changing, we're seeing the weather in southern Australia changed dramatically. Tell me how it works.
Joellen Russell: We've seen in both the northern and southern hemispheres the westerlies retreating towards the poles. So we have these winds that wrap around and around the mid-latitudes, and basically those belts of winds have been moving like shrinking doughnuts towards the poles of both hemispheres. And in the Southern Hemisphere it's been even more dramatic. In the north it's been about four degrees of latitude, in the south it's been six degrees of latitude. And since the westerlies carry most of our water in the winter onto land, when those westerlies move south they take those storms with them and therefore it is both drier and warmer in Australia.
Alexandra de Blas: Why are the westerlies shrinking?
Joellen Russell: There's two reasons. The first one is global warming where we have increased our CO 2 emissions dramatically and the CO 2 is basically warming our troposphere, the lower atmosphere, the atmosphere that we live and breathe in and where we see most of the expression of our winds. As this warming has been occurring, 0.8 degrees Celsius globally, that warming tends to push the westerlies basically towards the poles because we are warming from the tropics, pushing out. But also, and this is maybe even more important, the ozone hole has not healed, and as it is not healing, the temperatures are dropping in the stratosphere globally and particularly over the South Pole. So seven degrees cooler in the upper atmosphere over Antarctica.
It is the upper atmosphere, but in the winter when the polar vortex basically forms and opens over Antarctica, basically the stratosphere almost touches down on the top of Antarctica. So while the summers are quite a bit warmer, the winters are colder right now and these really frigid outbreaks of cold, cold air, essentially influenced by the fact that the stratosphere, which touches down in the winter, is seven degrees colder over Antarctica. And that temperature gradient is basically pulling the westerlies towards Antarctica because the westerlies are an expression of the maximum temperature gradient in the atmosphere.
Alexandra de Blas: Why is the stratosphere getting so much colder?
Joellen Russell: There's two reasons. One is that when the CO 2 traps more of the Earth's re-radiation near the surface, the stratosphere cools. However, it is also because with the loss of ozone...ozone, when it catches UV radiation, breaks apart, releasing heat. With no ozone to catch the UV, we get more skin cancer, but you also have a cooling stratosphere because no release of heat from the ozone catching the UV.
Alexandra de Blas: Now that we've got this gradient, what influence is that going to have then on this important circumpolar current that is so strong?
Joellen Russell: What it does is it basically drives the surface ocean much more strongly. So we expect to see the current increase. As we blow more water away from Antarctica, it's going to up-well more strongly, and we believe we already see this. We see melting right where we expect to see it on the Antarctic peninsular, growth of sea ice where it's coldest in the Ross Sea, these are exactly what one would expect from anthropogenic climate interference from both ozone perspectives and greenhouse gas warming. So we have multiple lines of evidence that this is exactly what is going on.
Alexandra de Blas: With these changes occurring, how is that affecting the ecosystems there?
Joellen Russell: This is really worrisome because on the one hand while the bonus would be that the global climate doesn't warm as quickly because the ocean can take up more heat and carbon dioxide, the downside is that heat is going into the ocean and it's melting sea ice and Antarctic ice. So the problem is that ice obligate species like penguins, species that require ice to live for their life cycle are finding it much more difficult. And I have a paper with David Ainley where we've used the climate models to predict how soon many of the established large penguin colonies will be in trouble, and our prediction is that by 2037 we anticipate basically three-quarters of the large penguin colonies will be wiped out.
Alexandra de Blas: In Antarctica?
Joellen Russell: Yes, that's right.
Alexandra de Blas: And why will they be wiped out?
Joellen Russell: Because their ice will melt. We're talking specifically here about Emperor and Adelie penguins, but they have particular ice needs during their life cycle basically to either nest on or feed from, and if that ice isn't there then their colonies won't be able to support themselves. There is also the work with Cynthia Tynan who is an expert in whales, and she and I have been working on a paper showing that where the up-welling occurs in the ocean is also moving towards Antarctica, and also potentially being more focused in smaller areas which are less accessible. Essentially the whales are going to be swimming further for less food. So these are real downsides to the fact that the heat is going in the ocean. We haven't even touched on the downsides of more CO 2 going in the ocean.
Alexandra de Blas: Ocean acidification is the impact.
Joellen Russell: That's it, ocean acidification is the other hard part, and there is a double whammy about this too. So, ocean acidification, as we add more CO 2 to the atmosphere, more of it will dissolve in the ocean. As it dissolves in the Southern Ocean in particular we are seeing where the water is really cold and we are quite close to the saturation state for aragonite, which is a form of calcium carbonate, and calcite as well, as we reach closer and closer to the saturation level where at that point you can no longer precipitate your shell if you are a little sea snail like a tetrapod, they are already seeing dissolution events down there. But that's only half due to the fact that we're putting in atmospheric CO 2 there's also the fact that that increase in up-welling water which we are talking about because of the winds is also contributing to acidification because it is up-welling water that is very acidic. We see an accelerating change in the pH of the Southern Ocean, which means the base of our food web there, the coccoliths, are under threat.
We are now pretty certain that there is no way that the winds will go back to their original position, that this is a longer term shift and that the ozone is not recovering like we expected it to. We are accelerating our emissions, so these things look relatively permanent. However, if we emit so many greenhouse gases, so much fossil fuel burning, and right now we are well above our high-end scenarios of 'burn it all', then eventually we could warm the surface so strongly that even the stronger winds would not be able to break through and continue to mix the Southern Ocean, at which point that's the end of our deep ocean sink for carbon dioxide. This is very serious but probably, unless massive mitigation goes on, inevitable.
Robyn Williams: Well, let's hope not, we like penguins. As for rains, what happens when La Nina stops? Joellen Russell is a professor of geoscience at the University of Arizona.
- Joellen Russell
- Assistant Professor of Geosciences
Department of Geosciences
University of Arizona
Tucson Arizona USA
- Alexandra de Blas
- de Blas Communications
- Robyn Williams
- David Fisher