Polar Ice Caps

WHY ARE THEY IMPORTANT AND WHAT’S HAPPENING TO THEM?

Greenland (near the North Pole) and Antarctica (South Pole) are home to most of the world’s glacial ice, including its only two ice sheets. Glaciers and ice sheets have been appearing in the news quite frequently in the past few years as they are increasingly unstable due to global warming. Just before Christmas it was reported that the Thwaites Glacier in the Antarctic, which is the widest glacier in the world and is sometimes referred to as the ‘Doomsday Glacier’, could collapse in as little as five years. Candice Moen has a closer look at our earth’s ice.

THE HISTORY OF ICE ON EARTH

There have been many ice ages on earth, most of them long before humans made their first appearance. These ice ages would have ranged from “comparatively mild” to “so severe that the entire Earth froze over for tens or even hundreds of millions of years”. Looking back over the history of these ice ages, the planet seems to have three main settings: ‘greenhouse’, when tropical temperatures extend to the poles and there are no ice sheets at all; ‘icehouse’, when there is some permanent ice, although its extent varies greatly; and ‘snowball’, in which the planet’s entire surface is frozen over. During the different greenhouse, icehouse and snowball there was ice present in various different locations across the earth’s surface.

It wasn’t until around 34 million years ago that the first small glaciers formed on the tops of Antarctica’s mountains (pictured below left). And it was 20 million years later, when worldwide temperatures dropped by 8°C, that the glaciers’ ice froze onto the rock, and the southern ice sheet was born. This temperature drop was triggered by the rise of the Himalayas (pictured below right). As the Himalayas grew higher they were exposed to increased weathering, a slow natural process during which minerals released from the rocks chemically bind to CO2, removing it from the atmosphere and reducing the greenhouse effect. The northern hemisphere remained relatively ice-free for longer, with Greenland and the Arctic becoming heavily glaciated around 3.2 million years ago. [Michael Marshall, newscientist.com]

QUATERNARY GLACIATION

We are currently in the Quaternary glaciation, which started just a few million years ago. The ice sheets have gone through multiple stages of growth and retreat over the course of the Quaternary. During “glacial” stages, the temperature is low and ice extends far away from the poles. During “interglacials”, the temperature is warmer and the ice retreats. The main trigger for the Quaternary glaciation was the continuing fall in the level of CO2 in the atmosphere due to the weathering of the Himalayas. However, the timing of the glacials and interglacials was driven by periodic changes in Earth’s orbit that affected the amount of sunshine reaching different parts of the planet. The effect of these orbital changes was amplified by positive feedback loops (a process in which the end products of an action cause more of that action to occur) such as changes in greenhouse gas levels. Between 130,000 and 114,000 years ago, the ice retreated during what is known as the ‘Eemian interglacial’ and then advanced again to create the glacial that most people know as “the ice age”.

When this came to an end and temperatures began to rise again, there were two final cold snaps. The Older Dryas transformed most of Europe from forest to tundra, like modern-day Siberia. After a brief respite, the Younger Dryas froze Europe solid within a matter of months, which was probably as a result of meltwater from retreating glaciers shutting down the Atlantic Ocean’s “conveyor-belt” current. Twelve thousand years ago, the great ice sheets made a final retreat at the beginning of the current interglacial (called the Flandrian) allowing humans to return to northern latitudes. This period has been relatively warm, and the climate relatively stable. Geologically, the cycle should continue to turn – this ‘icehouse’ period should someday come to an end and the ice sheets should descend again. Unless the effects of human activities on the climate, and runaway global warming being driven by positive feedback loops, disrupts the cycle. [Michael Marshall, newscientist.com]

COOLING THE PLANET

The polar regions of the Arctic and Antarctic are very important components of the global climate system – they are the cooling chambers of our planet. Having a very limited supply of solar radiation, they attract warm air and ocean currents from the tropics, cool them down and send them back towards the equator as floating ice. In this way, the polar regions regulate the distribution of heat on the Earth. Both the Arctic (North Pole) and the Antarctic (South Pole) are cold because they don’t get any direct sunlight due to the tilt of the earth on its axis. The area around Earth’s Equator gets a lot of sunlight in a small area but sunlight hits the polar regions at a shallow angle, which means the same amount of light is spread out over a larger area. There is another factor that contributes to the low temperatures of the polar regions – the albedo effect. When sunlight hits a white surface such as snow and ice, more of it is reflected back into space without warming its surroundings than when light hits a darker surface and is absorbed. [worldoceanreview.com]

The poles are covered with ice so a high percentage of the light that does fall on them is being reflected back into space instead of being absorbed and stored as thermal energy in the ground or ocean. Because these regions are so cold and dry, there is very little water vapour in the air to form clouds that will bounce the reflected light back to land.

WHAT WILL HAPPEN AS THE POLAR ICE CAPS MELT?

Rising sea levels is the consequence that we are all probably most familiar with, and it is very concerning. It is estimated that if Greenland were to melt today, sea level would rise globally by 7.4 metres, and Antarctica melted would add another 58 meters, which is a total of 65.4 meters/215 feet. The number of people that would be affected by this is about 40% of the world population because they’re within 250 feet of high tide. This rise in sea level will also cause groundwater salination of reserves further inland. Thermohaline circulation will be affected – these ocean currents move heat around the globe from the equator to higher latitudes and without them temperatures in Europe would plummet.

Less ice means less reflected heat, meaning more intense heatwaves worldwide. But it also means more extreme winters: as the polar jet stream – a high-pressure wind that circles the Arctic region – is destabilized by warmer air, it can dip south, bringing bitter cold with it. Polar vortexes, increased heat waves, and unpredictability of weather caused by ice loss are already causing significant damage to crops on which global food systems depend. This instability will continue to mean higher prices and increasing global food crises. Melting ice caps will also affect the Earth’s rotation because the axis of rotation is at the poles. Meltwater will flow away from the axis of rotation and the Earth will spin at a slower rate. Arctic ice and permafrost also store large amounts of methane, one of the greenhouse gases that contribute to climate change. When the ice thaws, that methane is released, increasing the rate of warming and reinforces the positive feedback loop.

IMPACT ON WILDLIFE

Our concerns are usually focussed on what the consequences will be for humans but it is essential that we also consider what these changes will mean for biodiversity. With a global biodiversity crisis that could see as many as half of all species facing extinction by the end of the century, we need to protect existing ecosystems for their sake too. When there’s less sea ice the animals that depend on it for survival must adapt or perish. Loss of ice and melting permafrost will spell trouble for polar bears, walruses, arctic foxes, snowy owls, reindeer, and many other species.

As they are affected, so too are the other species that depend on them in the ecosystem. Wildlife and people are coming into more frequent contact as sea ice habitats disappear. Wildlife will also be affected by all the factors affecting humans – rising sea levels, changes in ocean currents, changes in global temperatures, toxic chemicals being released in meltwater and methane being released by the permafrost.

Although there are natural glacial and interglacial processes that are also at play, our human activities driving global warming are having a very complex and dangerous effect on the ice caps of the Arctic and Antarctic. Many of the glaciers and ice sheets are unstable and unpredictable and, unfortunately, a lot of the damage has been done. We are now stuck in a massive positive feedback loop that we cannot reverse. We can only watch, and wait, and plan for the changes that are coming our way.

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