Scenes from another world, surely.
No towns or cities.
No greenery.
Almost no life at all.
Virtually all of the world’s fresh water is here, locked up in ice sheets over a mile
in thickness.
The harshest of all climates, these lands rarely see temperatures above freezing, and
have the lowest on record anywhere on our planet.
A land of ice, snow, glaciers, freezing winds and bitter cold.
This is the icecap.
In our series looking at climate zones from equator to pole, we have at last reached journey’s end
and the finale is anything if not dramatic, because it is here, in the most northerly
and southerly landmasses of Greenland and Antarctica, that we find the most extreme
of all climates, what is known by climatologists as the Icecap.
The climatic definition of Icecap is simple.
Average temperatures never rise above freezing.
The consequence of this will seem obvious.
There is no rain, no running water, just snow, usually blowing in from warmer regions around
it, which builds up over thousands of years into an ice sheet a mile deep or more,
meaning the surface of the ice is high above sea level, ensuring even lower temperatures
and further guaranteeing the icecap’s survival.
This process of thickening cannot go on indefinitely, of course, gravity demands that the ice be
pulled down to the sea, and as a large mass, over enough time, the seemingly solid ice
acts like a liquid, flowing toward the sea as glaciers.
When these glaciers reach the coast, then break off into ice bergs, to eventually melt
back into the ocean.
In the highest mountains of Earth, there are places where the temperature never rises above
freezing point, and so glaciers form here, in the Rockies, the Alps, the Caucasus, the
Himalayas and the Andes.
But by land area and amount of ice held, these areas are insignificant compared to the two
major ice sheets of the world – Greenland and Antarctica.
Despite qualifying under the temperature requirements, for the purposes of climate classification,
the Arctic around the North Pole is not usually included in the icecap climate, since there
is no actual land there, just frozen sea ice up to several metres thick at most.
Between them, Greenland and Antarctica account for 99% of the world’s fresh water, with
the vast majority of that share being in Antarctica.
The Antarctic ice sheet is almost ten times the size of Greenland’s, taking up an area
equivalent to the United States and Mexico combined.
If all of this ice was to melt, the sea level globally would rise by between 60 and 70 metres (approx. 200ft).
In the case of Greenland, it’s at first not clear why this land is covered in ice,
when the surrounding islands are tundra.
But unlike the surrounding lands, a wall of high mountains makes up what is believed to
be a giant set of three islands.
Millions of years ago, an ice age would have blanketed the whole area in a mile-thick ice
sheet, but as the ice age retreated, it is believed the mountains prevented this ice
from escaping quickly, and the high altitude of the ice cap maintained the very low temperatures
necessary to preserve its survival into the present day.
On the western coast of Greenland, there are a number of gaps in the mountains where the
ice flows out glacially, and on reaching the sea, these break off into icebergs which flow
down into the North Atlantic.
The ice berg that sank the Titanic began its life many thousands of years ago as snow falling
on the ice sheet that covers the world’s largest island.
In the case of Antarctica, there are multiple reasons why this giant continent stays covered
in ice, and why it is the coldest place on our planet.
The first is obvious – it sits right over the south pole.
In summer, sunlight strikes the earth here at an oblique angle, providing little warmth,
and most of what sunlight does arrive here is reflected back from the blinding white ice.
In winter, the sun remains below the horizon for months at a time, with consequently no
chance of any input of heat.
Secondly, Antarctica is surrounded by the unbroken Southern Ocean, allowing the prevailing
westerlies and the circumpolar ocean current at these latitudes uninterrupted travel, preventing
any movement of tropical air or warm ocean currents into the Antarctic region.
Lastly, Antarctica has had millions of years to build up its ice sheet, with the result
that most of the continent’s surface of ice is above 2000m (6500ft) in altitude, keeping
temperatures even lower than they would be at sea level.
In both Greenland and Antarctica, these high altitude ice sheets produce a special phenomenon
whereby the cold mass of air above the ice sheet seeks to fall into warmer air at the
coasts, since cold air is more dense than warm.
This leads to near constant winds, known as Katabatic winds, flowing out from the centre
of these land masses to the sea, sometimes reaching hurricane strength.
As if these places weren’t grim enough already.
In relative terms, despite the abundance of fresh water locked up the ice, this climate
zone is technically a desert, with most places experiencing less than 250mm of precipitation
per year (rain equivalent, not snowfall).
This is because the air is so cold that it can carry very little moisture.
Most of the snow that forms on the great ice sheets of Greenland and Antarctica blows in
from either adjoining tundra regions, or relatively warmer marginal icecap areas near the coasts.
In places in Antarctica, this combination of low precipitation and high winds causes
certain dry valleys to be scoured of all ice and snow.
In other parts, snowfall has never been recorded or suspected, suggesting that there hasn’t
been precipitation in centuries or possibly millenia.
This would make these places even drier than the Atacama desert in South America, which
is otherwise regarded as the driest on our planet.
Since average temperatures never rise above freezing, plant growth is impossible, and
in any case, the ground is covered with a moving layer of ice.
In some parts of the periphery of the ice sheets, moss and lichen grow on sunward facing
rocks, but this is the limit of any vegetation.
Despite this, however, a very famous set of animals have made Antarctica their home – these
little fellas, and these… big fellas…
Some species of penguins live in the Antarctic for the simple reason that there are no other
species here – no predators to interrupt their breeding cycles.
With the waters surrounding the continent being rich in fish, there is plenty of food
to sustain sometimes gigantic colonies, and these conditions seem to be worth paying the
price of living in the most inhospitable region on earth.
In terms of seasons, temperatures in Antarctica stay below zero throughout the year, but the
continent “grows” and “shrinks” in terms of area with the summer and winter,
as sea ice melts and freezes over.
During winter, only the extreme north of the Antarctic peninsula is directly accessible
by sea, with all other coasts blocked by frozen ocean.
Human settlement is confined to research stations on both the Greenland ice sheet, and in Antarctica.
The largest of these is McMurdo station on the coast of the Ross Sea in Antarctica, which
is accessible by ship in summer time, and among other functions acts as a supply base
for other research stations on the continent.
Then there is the Amundsen-Scott South Pole station, at the geographic bottom of our planet.
But this is not the coldest place on earth.
The official lowest recorded temperature at a surface based weather station occurred at
the Russian Vostok research station in East Antarctica.
On 21 Jul 1983, a temperature of -89.2°C (-128.7°F) was recorded.
More recently, a satellite recorded a temperature at the surface near Dome Argus, a snow dome
which is the highest part of Antarctica at an altitude of 4093m, and on top of an ice
sheet estimated to be at least 3km deep.
The temperature observed by the satellite was -93.2°C (-135.8°F).
Compare this with the average surface temperature of Mars, of -63°C, and you can see why the
icecap is considered the most other-worldly of all of Earth’s climate zones.
So all good things must come to an end.
I hope you've enjoyed the series, and learned a little bit more about the climates that
shape our world.
It's been quite a journey, travelling across twelve very different zones of Earth.
We witnessed...
The biodiversity of the Tropical Rainforests
The endless rhythm of wet and dry seasons in the Tropical Monsoon and Savannah.
The lofty temperate paradise of the Subtropical Highlands
The scorching drought of the Hot Deserts
The great cities of the Humid Subtropical
The idyllic coastlines of the Mediterranean
The beautiful countryside of the Oceanic
The remote and empty Cool Deserts
The great plains and cities of the Continental
The vast forests and extreme temperatures of the Sub-Arctic
The barren wastes of the Tundra
and the Icecap - as if it was in a different world entirely
In all these and so many other ways, it's a rich, varied and unique planet.
It's our planet.
Our Earth.
Our home.