PenguinScience | Climate Change
Bellwethers of Environmental Change
The following is a series of images, which with the information contained in their captions, should provide upper class high school students, college students and interested adults with the basic story about how one group of animals is responding, both in a positive and negative way, to global climate change.
Every species is adapted to exploit and cope with a set of factors that together determine where on Earth it can live. These factors include physical ones like temperature or rainfall, or biological ones such as the threat of predation by another organism, infection by parasites, or combinations of physical and biological factors. In the middle of this so-called zoogeographic range, a species is in ballance with the factors important to its existence and its population fluctuates little from year to year. As one nears an outer boundary of that range, however, one or more important factors begin to negatively affect the well being of that species and, depending on variation in the strength of that factor, the animal or plant may exhibit large fluctuations in abundance. Crossing that boundary, the species can no longer exist as that critical factor overcomes the capabilities of the species. At different boundaries, say, to the north or to the south, a different factor likely is critical, usually related in some way to climate. Earth’s climate has begun to change rapidly owing to human-related factors. As the change in global climate accelerates, species are responding to the change, some more successfully than others, and in different ways at different boundaries of their range. To illustrate how they do this, we’ve chosen as an example the Antarctic penguins.
Any species that occurs in the south polar region has to feel comfortable with ice or have adaptations to deal with it. Only some mites, wingless insects, some microscopic worms, bacteria and a few plants live on the Antarctic continent. The ice-covered oceans around the continent, however, are teaming with marine life.
The Adélie and Emperor penguin are two species that do not occur very far from ocean waters where sea ice is present for at least part of the year. In fact, these penguins are obligate associates of sea ice, much like many songbirds are obligate associates of forests. Given that any ice is highly sensitive to changes in temperature, these two species are likely to be sensitive to global warming. The Adélie Penguin is probably unique among Earth’s animal inhabitants: not only do we know how it responds to changes in its present environment, but unlike most other creatures we also know how it has responded to habitat and environmental changes for at least the last 35,000 years. Unlike Adélies, on the other hand, we know relatively little about how the Emperor Penguin responds to changes in its environment because 1) the species breeds during the dark of winter and is thus very difficult to study, and 2) they nest on sea ice that periodically melts or breaks up and thus usually they leave no trace of their existence from year-to-year, much less for thousands of years. Nevertheless, they are still highly sensitive to changes in sea ice conditions and offer us some lessons about how any species might respond to changes in climate.
Adélie Penguins can tell us so much about climate change and how climate change affects Earth’s living things, because 1) there has been a lot of research on this species’ current habitat requirements, with complete data records extending back for 50 years; 2) the major feature of its habitat (ice, both land and marine) is now ‘easily’ quantified and monitored by NASA satellites and other remote sensing devices; and 3) the dry, cold Antarctic environment has preserved Adélie Penguin bones since before the last time that glaciers grew on Earth, i.e. since before the last Ice Age (which occurred 25,000 to 12,000 years ago). By determining how old these bones are we know much about this species’ past in regard to variations in sea and land ice (glaciers). Using these clues from present and past we have a good chance to successfully predict how these penguins will respond to climate change in the future.
Penguins, however, are sensitive to more than just physical aspects of their environment. Recent research has shown them to be exceedingly sensitive to prey availability as well. Since they are different from most other seabirds in that they can’t fly, they are unable to easily search increasingly larger areas looking for food should it become hard to find. They rely on food in predictable amounts and quality, in predictable places. Thus, the major uncertainties regarding these species and environmental change are 1) how these penguins will respond to climate change given the destruction of their food web by human fisheries, a factor they have experienced very recently (only in the last hundred years, as compared with the 2.5 million years of their existence on Earth); and 2) what will be the consequences of the high rate of climate change going on now, which has occurred only a few times in the history of Earth. The last time a Rapid Climate Change Event occurred was about 12,000 years ago, at the end of the last Ice Age, when Earth’s temperatures rose several degrees in just one or two decades.
This map, based on data from NASA, shows the difference in ice extent
between winter, when Antarctic sea ice is at its maximum, and late summer, when it is at its minimum. In both seasons the ice extends from where waters are warmer than -1.7oC (about 29oF) to the edge of the Antarctic continent, where it is very cold, especially in winter. The Antarctic Polar Front marks the northern (warm) boundary of the Antarctic; the line labeled “ACC” marks the southern limit of the Antarctic Circumpolar Current that flows west around the continent, between it and the Polar Front. The southern boundary of this current affects where the northern boundary of sea ice will occur, an important detail. Adélie Penguins and all but first-year Emperor Penguins travel no farther north than the limit of winter ice.
Between winter (May), when Emperor Penguins begin breeding, and spring (October), when Adélie Penguins begin breeding, the sea ice in the Southern Ocean is very extensive (see previous map) and the openings between ice floes, especially as one travels farther south, become very narrow or disappear all together. Therefore, both species of penguins establish their colonies in areas that are close to polynyas, a Russian term that refers to areas of persistent open water or loose pack ice in otherwise heavily ice-covered seas. Most Antarctic polynyas form when persistent, strong winds sweep off the continent and push away the sea ice; unlike the Arctic there are few polynyas formed by the upwelling of warm water. This map shows the proximity of penguin colonies to coastal polynyas in one section of Antarctica.
This image shows what a polynya looks like from a penguins’ perspective. These penguins are standing on an ice floe that is at the edge of a wind-swept polynya. Without the wind acting to keep the polynya ice-free, the penguins might have more difficulty, requiring walking, to find a place to dive into the ocean.
Emperor Penguins breed at locations where the sea ice is locked in place by grounded icebergs, islands or capes. In this view, taken from a helicopter at about 300 m altitude , the Emperor colony can be seen as a large cluster of dark dots on the ice.
These Emperors are standing on the sea ice next to a glacier that keeps the ice locked in place. The ice must remain stable from about April until the end of December for them to complete an entire breeding season. If the ice is too thin and breaks up too soon then the chicks will be swept to sea before they are ready to take care of themselves.
The Emperor Penguin colony at Pt. Géologie is the site of where “March of the Penguins” was filmed. It is among the northernmost of all Emperor Penguin colonies and thus has relatively warm weather compared to most of the rest of Antarctica. In fact, it is near the northern edge of this species’ range; where most Emperor Penguins nest it is much colder. Emperors have been studied for a long time by French biologists associated with the Dumont d’Urville research station nearby.
As shown in this graph (data from Barbraud & Weimirskirch 2001), the Pt. Géologie colony began a sudden decline in the mid-1970s and has since failed to recover, probably due to warming winter temperatures that have resulted in thinner fast ice on which they breed. The strong Antarctic winds have thus been able to blow the ice away before the chicks were ready to fledge. It is this loss of chicks that has prevented the colony’s recovery. At Taylor Glacier, another Emperor Penguin colony (studied by Australian biologists) in the same section of coastline but several hundred kilometers to the west, the Emperor Penguin population has not declined much, if at all, during the same time period. This is probably because it’s but one of only two sites where this species of penguin nests on land, and is thus not dependent on the presence of persistent sea ice for their breeding success. Most Emperor Penguin colonies, much farther south, so far have not experienced sea ice that is too thin for the species’ needs.
Lessons from Past Environmental Change
Besides knowing how Adélie Penguins are responding to current physical changes in their environment brought on by global climate change, we know a lot about how they responded to past changes, especially as the Earth warmed since the last Ice Age (ending ca 12,000 years ago). That information helps us to predict how these creatures will respond to future climate change. We are beginning to understand, too, how this species responds to alteration of the abundance of its food, which makes it more sensitive to changes in physical habitat.
The reason we know so much about how this species has responded to previous changes in its environment is because its bones are preserved by the cold, dry climate characteristic of high-latitude Antarctica. Elsewhere on Earth the bones of animals disintegrate within decades. This penguin mummy is several hundred years old. It has been worn down by the feet of other penguins walking over it and by being sand- and snow-blasted by the wind. The age of these remains can be determined by assessing the amount of a certain form of carbon (carbon 14, or C14) in its tissues; C14 occurs naturally in Earth’s atmosphere and is incorporated into the penguins tissues (and all animals’ tissues) while it is alive. The C14 disappears over time from tissues at a known, constant rate once the animal dies. If mummies like this one are found along with the bite-sized rocks that Adélie Penguins use for their nests (not too large that the penguins can’t carry them in their bills, and all of the same size), then we know that the mummy’s location was once a breeding colony. Pieces of egg shell can provide additional clues if one digs below the surface. Such “sub-fossil” records (old things not yet turned to stone) tell us that the area has been ice free since at least the oldest dated mummy present; otherwise the bone deposits would not occur there.
More than 95% of the Antarctic coastline looks like this: sheer cliffs of ice and rock meeting sea ice at their bases. Adélie Penguins cannot make their colonies in these locations because they need ice-free land with a supply of small rocks with which to build nests, and although they are very nimble they are unable to climb tall cliffs. Also, they don’t like to walk very far over ice to find the open water they need for feeding. Emperor Penguins could breed here (on the sea ice), but in many places they don’t because the ice breaks out and melts too early in the spring. Because of these factors, suitable nesting habitat for both penguins is very hard to find. In fact, the southern limit of their ranges is defined by the Antarctic coast, which is mostly glacial ice (see Image 1).
Here is an Adélie Penguin colony, Cape Crozier, which is located at
the edge of the continental glacier that covers West Antarctica (the West
Antarctic Ice Sheet). This part of the glacier is called the Ross Ice Shelf
because it is floating on the sea (like a shelf extending out from the continent).
It is the largest glacier on Earth. During the last ice age, Adélie
Penguins did not nest here because the front of the Ice Sheet was located
much further to the north, covering the entire Ross Sea and thus blocking
off this Cape. They began to nest here within the last couple of thousand
years, ever since the Ice Sheet retreated, enabling a southward extension
to their breeding range. We know this from the age of the mummies that have
been found. The Ice Sheet retreated because pieces broke off, as ice bergs
(as shown here), at a rate that was faster than the amount of snow falling
in the Antarctic interior and which was maintaining or adding to the ice sheet.
In other words ice loss was greater than ice accumulation.
There are no penguins currently nesting at this site on Beaufort Island, in the central western Ross Sea. However, fossil remains reveal an area that Adélie Penguins used to occupy before the last Ice Age (!), but which they were forced to abandon due to the advance of the West Antarctic Ice Sheet. By dating the penguin remains, we’ve learned that the species has been absent from this location for over 30,000 years. The birds are just now beginning to return owing to an apparent retreat of the snowfield and thus increased access to a snow-free location with lots of stones with which to build nests.
In many parts of the world, glaciers are retreating at increasing rates as a result of global climate change (warming). We don’t know if the particular glacier shown here has accelerated its retreat from what it has been since the last Ice Age. But, it illustrates a point. The retreating glacier is benefiting Adélie Penguins because it has retreated far enough from a very gentle slope to allow the penguins to come ashore to found a colony. The colony here, at Cape Bird, Ross Island, is the light brown area (penguin guano deposits) in the middle ground, with the dark rows being groups of nesting penguins (elevation from where the photo was taken is about 300 m). The upper half of the image shows an ocean that at the time this photo was taken was covered by sea ice.
As glaciers retreat, they also leave piles of gravel, called moraines (little rocks ground from big rocks by the incredible weight and slow but steady movement of the glacier). These deposits supply the stones used by Adélie Penguins to build their nests.
These penguins are nesting on the shores of a bay that is now completely covered by fast ice (Cape Royds, McMurdo Sound). Fast ice is sea ice that is attached to the shoreline and has very few openings through which penguins can dive into the waters beneath. If it becomes too cold, as during the last Ice Age, and this extensive sea ice persists through the summer, then this colony would cease to exist because the penguins would have to spend too much time and energy walking over the ice to get from their nests to open water. In fact, this colony’s population has been declining over the past six years because the fast ice has failed to beak out owing to a recently grounded iceberg and a lessening of winds. There are still many parts of the Antarctic coast that are too ice-choked to allow penguins to establish colonies. As the Antarctic warms, however, the sea ice in these areas will begin to break up, creating more areas where, if there are some gentle beaches, Adélie Penguins could one day nest.
THE RESPONSE TO CURRENT ENVIRONMENTAL CHANGE
Shown here are the changes in colony size of the two southernmost penguin colonies in Antarctica (77-78oS latitude). Biologists from LandCare Research (New Zealand) have been counting the penguins nesting in these colonies for 4 decades (these data from Wilson et al. 2001). These colonies are on Ross Island in the southern Ross Sea. The colonies, especially the small ones, have been growing as a result of changes in their environment brought by two important factors. First, global climate change, especially increased wind strength and warmer winter temperatures, has resulted in thinner sea ice and a more persistent polynya, particularly the one in McMurdo Sound, where two growing colonies are located. By being able to swim to their foraging areas, they can eat their fill of food much more quickly and can bring more food back with them when they return to their nests. Thus, their breeding success has increased and their population within this group of colonies has grown.
The second factor that has facilitated the growth of Adélie Penguin colonies in the Ross Sea, and likely other high-latitude areas of the Southern Ocean, is the extraction by whalers of their main competitor for food, the Antarctic minke whale. When the numbers of whales increase near a penguin colony, which happens periodically, the penguins find it more difficult to obtain food. That is to be expected, though, as both species are denizens of pack ice and have been together for 3 million years. It could be that where minke whales are especially abundant, that might be one of those factors that limit the number of penguins present. During the last few decades, as sea ice conditions have made life more favorable to Adélie Penguins so has the killing of minke whales by Japanese whalers. This seems to have contributed to the Adélie Penguin increase at the southern limit of their range but also disrupts the foodweb in which both species evolved.
This is the trend of an Adélie Penguin colony at the northern tip of the Antarctic Peninsula (see map below; data from Bill Fraser in Ducklow et al. 2007). It is located at the extreme northern (warm) edge of where this species occurs on Earth. The air temperature in this area has been warming rapidly (several degrees in the last 50 years), resulting in sea ice failing to form during winter and spring. Because Adélie Penguins are especially adapted to the cold conditions associated with sea ice and do not compete favorably with other penguins which are less adapted to the cold, the overall population has been declining at this and nearby colonies, and any young produced have chosen to nest farther south where sea ice remains. Eventually, Adélie Penguin colonies in this area will disappear, leaving only nest stones and mummies behind. Other species of penguins (such as Chinstrap penguins), if fisheries do not deplete their prey, may move in to replace the Adélies. If global warming begins to influence the more southern reaches of the Antarctic continent, then the entire world’s population of Adélie Penguins could be at risk.
Besides the loss of sea ice at the northern tip of the Antarctic Peninsula, the warmer atmosphere is holding more moisture there, which in turn results in greater deposits of snow. The Adélie Penguin needs snow-free areas to breed, if only to be able to find stones to build its nests. Heavier snow fall, then, would cause suitable nesting areas for this species to disappear.
The image here shows the change in the persistence of sea ice that rings
Antarctic in any year. The data are from NASA satellites collecting
information since 1979. This has been a period of accelerating warming in
western Antarctica, and cooling in eastern Antarctica. Both changes are a
result of the climate change that is affecting all of Earth. The reason
that the change is not uniform over all of Antarctica has to do with how
wind and weather patterns are adjusting to the warming in certain parts of Earth’s atmosphere, changing in different ways in other parts. Note here,
that at the tip of the Antarctic Peninsula in western Antarctica (top,
left), Adélie Penguin colonies are disappearing as sea ice becomes reduced. In addition, some of the penguins' prey species in this area have been depleted by human fishing as well. In the remainder of Antarctica, where sea ice extent has not yet been negatively affected, and where increasing coastal winds have maintained access to food, Adélie Penguin colonies have remained in balance with the environmental factors that affect their existence. In some areas retreating glaciers and thinning sea ice have allowed Adélie Penguin populations to increase. Click on image for larger version.
As temperatures of Earth continue to warm, eventually all of Antarctica’s sea ice will be retreating. As we’ve seen, sea ice is at the core of factors that determine these species’ existence. Adélie and Emperor penguins will continue to live where sea ice exists, and even colonize new locations along the coast where the sea ice becomes more open, and land glaciers retreat. Eventually, however, these penguins will disappear sequentially farther and farther south as the sea ice disappears, and as their prey disappears as humans overfish and alter the foodweb of the Southern Ocean. At the same time, sea level will be rising as the West Antarctic Ice Sheet melts. The rising sea level will cover low lying coast where the penguins otherwise would found colonies. Of course, if this occurs the streets of New York, London, Amsterdam, Calcutta (?) and many other cities will be covered, too.