Primer: Ice on the Earth’s surface

In front of the Fox Glacier, New Zealand

In front of the Fox Glacier, New Zealand

I started this blog to be able to share what I do with the world, in a way that is hopefully accessible to everyone! First though, I should introduce the subjects that I am interested in. The first topic I am tackling is “ice on the Earth’s surface”. Reading the reactions to news stories of climate change, there seems to be a lot of confusion regarding ice. One of the problems is that the huge quantities of ice that exist on the Earth’s surface are very far away from populated area. This means it is hard for people to envision what the changes in the cryosphere (the frozen areas of the Earth) means to them. So here we go.

1) Ice as precipitation

A snowy day at Stockholm University.

A snowy day at Stockholm University.

No matter where you are in the world (unless you live in an extremely tropical area) there is the possibility of experiencing ice as precipitation. Whether it is snow, sleet or hail, ice has an effect on human activities and infrastructure. Although things like hail and sleet can be bad news, snow is the most important form of precipitating ice. In relatively temperate areas, snow protects the land from the harsh winter climate, and when it melts, it provides fresh water. One of the notable problems with the present drought in California, for instance, has been the lack of snow in the Sierra Nevada mountains. Since the snow takes time to melt in high elevations, it provides a slow release of essential water. Ice can also form from deposition directly from water vapour (think frost). This can be an important way for ice to accumulate in places that are very cold and far away from a source of moisture.

2) Sea ice

Pancake ice - the beginning stage of sea ice

Pancake ice – the beginning stage of sea ice

Sea ice is ice that forms when ocean water freezes. Since the ocean is full of salt, and tends to have a lot of waves, it can only form when the air temperatures are quite cold. The above picture was taken in Svalbard in the relatively sheltered confines of Isfjorden, where temperatures were below -10C in April. And even then, the sea ice breakup was already well underway!

Because sea ice sits on ocean water that is constantly flowing, it tends to be transient. Even in the middle of the Arctic Ocean, ice that has existed for years will eventually find its way off to the edge and melt away! One of the big concerns in climate science is that the amount of ice that survives for multiple years in the Arctic has diminished significantly since the 1970s. This means that it is easier for the Arctic sea ice to melt away in the summertime, which has follow on effects for weather patterns in the Northern Hemisphere. This decline has been the focus of intense study.

While the Arctic sea ice has shrunk, in many parts of Antarctica, the sea ice extent has expanded in recent years. While doing my PHD, I heard all about the problems this caused, as the resupply vessels had trouble reaching the Australian Antarctic bases. While the culprit for the disappearance of Arctic sea ice is pretty easy to pin down (warming atmosphere and ocean), the cause of Antarctic sea ice expansion is more nuanced. One of the proposed mechanisms is that the increased gradient in upper atmospheric temperature between the tropics and south pole (due to the hole in the ozone layer) has caused an increase in wind speed at the surface. The increased wind pushes the sea ice further away from Antarctica, and also opens the ocean for further ice formation. It is also possible that the upper layer of the ocean around Antarctica is become fresher due to increased precipitation. Don’t let it fool you, though the sea ice around Antarctica is increasing, Antarctica on the whole is becoming significantly warmer than in the past.

3) Glaciers

In front of Mýrdalsjökull (Mire Dale Glacier) that flows from an ice cap on the Katla volcano.

In front of Mýrdalsjökull (Mire Dale Glacier) that flows from an ice cap on the Katla volcano in Iceland.

Glaciers are flowing masses of ice. This happens when ice buildup is great enough that it starts to deform under its own weight. The conditions for the existence of a glacier can be quite variable, as explained below.

For temperate glaciers, such as Mýrdalsjökull in the above picture, the glacier exists as long as there is enough snow accumulating in the upper reaches of the glacier.  Right now, the Mýrdalsjökull glacier is in a state of rapid retreat due to warming in the region. In Iceland, one of the glaciers has thinned so much, that it no longer flow, and therefore can’t be classified as a glacier.

Debris within Longyearbreen

Debris within Longyearbreen

In colder climates, a glacier’s existence is much less threatened. Even if the amount of snow in polar environments is quite small, if there is little melting during the summer, the glacier will continue to exist. Even if it is very cold, a glacier can still flow very slowly. To the right is a good example of this. It is a photo of a chunk of sediment that has been incorporated into the Longyearbreen (Longyear Glacier) in Svalbard. Although the flow of the glacier is extremely slow (about 3 m per year), the evidence that it is moving is right there.

One of the most noteworthy Glaciers that has captured a lot of press during the past few years has been the Jakobshavn Glacier in Greenland. This is an extremely fast flowing glacier that drains about 6-7% of the Greenland Ice Sheet. The iceberg that sunk the Titanic is suspected to have come from it. After a few decades at a relatively stable position, it began to retreat rapidly in the early 2000s. This glacier has been studied intensely over the years, and serves as an ideal laboratory to see how ocean-glacier interactions work. Scientists are concerned that the rapid disintegration of Jakobshavn is an indication that recent global warming is causing a major effect on Greenland.

4) Ice Sheets

The Greenland Ice Sheet (from Google Earth)

The Greenland Ice Sheet (from Google Earth)

Now, onto what I am most interested in – ice sheets. Ice sheets are large, continent sized masses of ice. They currently exist in Antarctica and Greenland, though in the past they also covered northern North America and Europe. Ice sheets consist of domes of ice, with branching glaciers that drain them. In the center of the ice sheet, the velocity is close to zero. This allows scientists to drill cores, and analyze past climate conditions, with ages determined by counting the annual layers of ice accumulation (yes, it leaves nice layers!). The velocity of the ice is typically highest where the glaciers terminate in the ocean, as the ocean erodes underneath the ice, provides lubrication at the base, and causes buoyancy forces that eventually break the ice (not to mention that the temperatures at the coast are warmer than in the interior).

The Antarctic ice sheet is typically considered to be two ice sheets. The East Antarctic Ice Sheet is the more massive of the two, covers most of the Antarctic continent, and is the most stable ice mass in the world, having survived for possibly millions of years. The West Antarctic Ice Sheet, the smaller of the two components, is on an archipelago (island chain), and so most of the ice sheet lies on a bed that is below sea level. When people talk about ice sheet collapsing, they are mostly referring to the West Antarctic Ice Sheet, as it is vulnerable to interactions with a warming ocean. The two ice sheets are separated by the Transantarctic Mountains. The Greenland ice sheet is also vulnerable to a warming climate, due to its proximity to the more temperate Atlantic Ocean.

When it comes to proclamations of collapse, it is useful to refer to the ice sheets that covered North America and Europe. They were massive ice sheets that were comparable in size to the existing ice sheets on Greenland and Antarctica. They reached their maximum size between 26,000 and 18,000 years ago. Just 10,000 years after that, they were mostly gone. To a geologist, this is a blip on the radar. However, I will discuss paleo-ice sheets in a future post.

5) Ice Shelves

Early Larsen B ice shelf collapse in 2002 (from NASA)

Early Larsen B ice shelf collapse in 2002 (from NASA)

I’ll finish off with a discussion on ice shelves. Ice shelves are basically the floating extension of glaciers that terminate into the ocean. They act as a buffer to prevent glaciers from flowing rapidly. When that buffer is gone, an ice sheet can start to collapse, as the glaciers can move more ice into the ocean. This process was pointed out in a big news story earlier this year that the Larsen B Ice Shelf was on the verge of breaking apart. It should be noted that large scale collapse of the ice sheet really began in 2002, and the more recent study basically says that there will be little left by 2020.

I won’t say anything more than this on ice shelves (which is beyond my area of expertise), except to say that one of the most common errors that climate deniers make is mistaking the ice shelf collapse that is happening to shelves all around West Antarctica, and the trend of growing sea ice. These are two very different types of ice! The growing sea ice trend is not going to change the fact that the West Antarctic Ice Sheet is largely below sea level, and that removing the ice shelves will cause the glaciers to flow faster, which will cause an increase in global sea level.

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