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Antarctica Global Warming - FullFull

The effects of Global Warming on Antarctica

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Rising temperatures cause ice shelves to break up - as they are floating already this will not affect sea levels, it may cause the glaciers behind them to speed up their flow-rate considerably. These glaciers will add to sea-level rise if they melt.

The temperature of Antarctica as a whole is predicted to rise by a small amount over the next 50 years. Any increase in the rate of ice melting is expected to be at least partly offset by increased snowfall as a result of the warming.
Global Warming in Antarctica - summary of this page
  The situation is not so much changing constantly, rather it is being assessed constantly and changes that may have already occurred (such as the decline in krill - below) are being discovered.

New research is being carried out, new things found and understanding is improving. For the foreseeable future, global warming in Antarctica is likely to be a fairly lively topic, for the latest news try here

I wrote these pages after reading an awful lot of articles, scientific explanations and news reports*, these statements summarize the situation as I understand at the moment:

*ALWAYS take news reports in the papers, offline or online with a pinch of salt, the real purpose of many newspaper stories is very often to sell newspapers and/or gain some fame or career progression for the journalist. There have also been a number of "bandwagons" spring up about the whole subject of global warming / climate change which has become a very political subject.

Global warming is real, it is happening more quickly in some parts of the world than others.

The Antarctic Peninsula is particularly sensitive to small rises in the annual average temperature, this has increased by nearly 3°C in the region in the last 50 years, this is about 10 times faster than the average in the rest of the world. This makes it an excellent study area.

The temperature of the rest of Antarctica - the other 96% - shows no current indications of rising.

There is no unusual significant loss of ice of any kind from the larger 96% of Antarctica that is not the Peninsula.


Image courtesy NASA

1/ What evidence is there from ice?
The Larsen B Ice Shelf
LarsenB iceshelf, 17th Feb 2002
Larsen B ice shelf, 17th Feb 2002
Larsen B iceshelf, 5th March 2002
Larsen B ice shelf, 5th March 2002 (16 days later)
dimensions of photograph area approx. 130 x 160 km (80 x 100 miles)

The break-up of the Larsen B ice shelf in early 2002. This event has been attributed to the effects of global warming. That it occurred is beyond dispute and that it is a result of the warming of the Antarctic Peninsula where it is situated is also beyond dispute. What remains unclear is whether or not this is a taste of things to come and an indicator of an Antarctic-wide phenomena or simply a localized result of the localized warming of the Antarctic Peninsula region alone.

An ice shelf is a thick layer of ice that is floating on the sea. They are fed from the land by glaciers. Where the ice leaves the land and starts to float on the sea is a region known as the "hinge zone" where the ice is particularly chaotic, broken-up and a nightmare to try and travel over. Ice shelves surround much of Antarctica.

The Larsen B ice shelf was about 220m thick (720 feet) and during a 35 day period in early 2002 lost about 3,250 km2 of ice into the ocean. It is thought to have been in existence for at least 400 years prior to this and probably as long as 12,000 years since the end of the last ice age.

Such a disintegration in such a short time period is therefore an extremely significant event. What now remains of the Larsen B is about 40% of what was there in 1995. It had been breaking up at what was considered to be a rapid rate anyway before this major event. The break-up is thought to be a consequence of higher temperatures and large amounts of summer melt-water running down crevasses in the ice shelf so speeding the disintegration process.

Overall in the Antarctic Peninsula, seven ice shelves have between them declined in area by about 13,500 km2 since 1974.

A more recently seen phenomena that follows this ice shelf collapse is that the glaciers that fed the ice shelf seem to now be speeding up their flow down to the sea. This will certainly deposit more water in the oceans, and as this was previously on the land it will add to an increase in sea-level. The Antarctic peninsula doesn't have enough ice to make much of a difference to sea level in itself even if it were all to melt, but it is best seen as an indicator region that can be observed to enhance understandings of the mechanisms in other parts of the world.


Prince Gustav Channel

Evidence from seabed sediments in the Prince Gustav Channel on the Antarctic Peninsula after the ice shelf that previously blocked it collapsed has shown that it had disappeared at least once before in the last 10,000 years.

"Thus, the present loss of ice shelves cannot be assumed to be a consequence of Man-made climate change, unless and until a cause can be identified"
British Antarctic Survey


The Prince Gustav Channel in 1985

A photograph that may not be able to be taken again for a few hundreds or even thousands of years. In 1985, HMS Endurance is  moored up to the ice barrier that blocked the Prince Gustav channel between James Ross Island and the Antarctic Peninsula. Standing by the ship and looking to the left in the picture, the ice slope could be seen to rise to well over 100 feet (30m) altitude into the distance (and 9 to 10 times that thickness under the level of the sea). Today, the whole lot has gone.


West Antarctic Ice Sheet (WAIS)

The West Antarctic Ice Sheet (to the west of the Antarctic Peninsula) has thinned significantly as a result of warmer temperatures in the surrounding Antarctic Ocean. The upper ocean in this region has increased in temperature by more than 1°C since 1955. The greatest degree of thinning has happened in an area called the Amundsen Sea Embayment.

Many glaciers have retreated and 10 ice shelves have been seen to retreat in recent years. 87% of glaciers along the west coast of the Antarctic Peninsula have retreated in the last 50 years with most of these showing accelerated retreat in the last 12 years.


Ice Cores


Picture courtesy - Hannes Grobe, Alfred Wegener Institute for Polar and Marine Research - Creative Commons Attribution-Share Alike 2.5 Generic license.
Antarctica has ice that is up to 4700m thick. This ice preserves a record of the conditions at the time it was frozen, of the amounts of gases in the atmosphere and an indication of the temperature. The deeper you drill, the further back in time you go.

Research into ice cores show that current atmospheric carbon dioxide and methane gas levels (both greenhouse gases) are higher than at any time in the last 800,000 years. The rate of increase of these gases is faster than any likely to have happened in the recent geological past. This 800,000 year record came from a 3km long ice core.

2/ Is the whole of Antarctica warming?
No.

 The Antarctic Peninsula, particularly the West coast of the Peninsula is warming at a rate about 10 times faster than the global average. This has received a great deal of publicity in recent years and of course is where the Larsen B ice shelf (see above) is situated. The average annual temperature of this region has increased by nearly 3°C in the last 50 years.

However, data on temperatures in Antarctica only really go back about 50 years, anything beyond that is surmised from ice cores or other sources and so we don't really know how the temperatures vary over even the medium term in Antarctica.

The Antarctic Peninsula also represents only about 4% of the whole continent, the other 96% appears to have had a stable temperature over the last 40 years to the extent where the most remarkable aspect is the stability compared to other parts of the world.

One reason that the Peninsula region appears to be so dramatically warming is that it has a large amount of snow and ice, glaciers, ice shelves and other features and also has an annual average temperature not far off the freezing point of water. A small increase in the average annual temperature can mean that a few more weeks or even just a few more days per year when melting can occur can result in very visible results of ice features reducing or disappearing.

The vast majority of Antarctica is so cold that even if the temperature was to rise by the same amount as the Peninsula, there still wouldn't be any melting going on at all. The average surface temperature of continental Antarctica is about -37°C as opposed to -5°C for the warmest places on the peninsula.

1 - A warm day in most of Antarctica still gives a temperature well below freezing result;

= Nothing much to see.

2 - A warm day in the Peninsula could take temperatures above freezing point so the ice begins to melt, result;

= Lots of melting and potential ice break up.

This is no reason to become complacent however as part of the reason that the Antarctic ice sheet is so cold is that it's so high, due to the thickness of the ice. The melting and flow of the glaciers removing ice from the continent is also slowed by the ice shelves around the continent edge.

Small rises in temperature that start to nibble away a little faster at the edges could eventually speed up the loss of ice and cause greater temperature rises to take place further inland. Ice shelves seem to act as "corks" in the Antarctic "ice-bottle", remove the ice shelf and a huge amount of ice from the interior could start to flow towards the sea where it will melt even though the temperature in the interior may be stable. The "corks" are currently keeping the ice at the coldest places.

The problem with trying to predict the future in these matters is that firstly there is not enough data available to base predictions on and secondly, the way things work is not fully understood. Most models from different researchers and teams tend to agree however that there will be some small changes in temperature over the next 50 years. It is also expected that the rise in global temperature will put more moisture into the atmosphere and more of this will reach Antarctica so giving a greater snowfall to offset the melting ice. Despite all the snow and ice there Antarctica is actually classed as a desert as there is so little snow-fall, it's just that what does fall stays there so it builds up over a long time period.

3/ Are there any biological effects of global warming in Antarctica?
Plants
Deschampsia antarctica - Antarctic hair grass on the Peninsula
picture use Claurabert - GNU Free Documentation License, Version 1.2
Antarctica's only two flowering plant species that grow only on the Peninsula have spread considerably in the last few decades in both geographic distribution and also abundance in the areas where they are found. In some areas they are becoming the dominant species.

Part of the reason for this is that there has been a switch from snowfall to rainfall during the summer. This means that more water is available physiologically to the plants rather than being locked up as ice crystals and so unavailable.

Melting ice and permafrost has led to newly available land that has become colonized by plant, animal and microbial communities.






Penguins

Adelie penguins on sea iceAdelie penguins (Pygoscelis adeliae) have also been suffering a steady decline in parts of the Antarctic Peninsula region for the last 20 years. Adelies are reducing in number and abandoning certain nesting sites while Chinstrap penguins (Pygoscelis antarctica) are taking their place. Adelies require pack ice for most of the year and feed almost exclusively on Krill, Chinstrap penguins will eat a wider variety of foods and prefer open water. The sea ice has declined over the last 20 years with the rise in temperature in the Peninsula region.

Gentoo penguins (Pygoscelis papua) have also started to nest on the Peninsula in recent years, for the first time in living memory (and it needs to be noted that any memory of Antarctica doesn't stretch much beyond a hundred years). Studies of the bones and remains found in abandoned colonies indicates that prior to 1950, no Gentoo penguins nested in these sites at all.

On the other side of Antarctica, the Ross Sea region and East Antarctica however, Adelie penguin colonies have remained stable or even increased.


Krill

Studies (November 2004) have shown that stocks of krill in Antarctica have declined dramatically in recent years. The reason for this is likely to be a fall in the amount of sea ice in the winter months in the Antarctic Peninsula region.

krill, Euphausia superbaKrill numbers may have dropped by as much as 80% since the 1970's - so today's stocks are a mere 1/5th of what they were only 30 years ago. The decline in krill may  in turn account for the decline in the numbers of some penguin species.

Dr Angus Atkinson from British Antarctic Survey, says:

"This is the first time that we have understood the full scale of this decline. Krill feed on the algae found under the surface of the sea-ice, which acts as a kind of 'nursery'.

The Antarctic Peninsula, a key breeding ground for the krill, is one of the places in the world where there has been the greatest rise in temperatures due to global warming. This region has warmed by 2.5°C in the last 50 years (much more than the mean global rate), with a striking consequential decrease in winter sea-ice cover.

"We don't fully understand how the loss of sea-ice here is connected to the warming, but we believe that it could be behind the decline in krill."

There are commercial implications as well as scientific ones. The Southern Ocean is a valuable fisheries resource, many of the species caught feed on krill. Thousands of tourists are also attracted to Antarctica to enjoy the spectacular wildlife, most of which feed on krill.

There has been previous speculation that krill stocks might have decreased, based on smaller more localized surveys over shorter time periods. This new finding comes from data from nine countries working in Antarctica who pooled their separate data covering 40 Antarctic summers, in the period between 1926 and 2003. This is the first time such a large-scale view of change across the Southern Ocean has been seen.

Another animal that feeds on the same phytoplankton food as krill, jelly-like colonial animals called salps that drift in the ocean currents have increased in the same time the krill have decreased.

This decline in krill will also make it more difficult for the great baleen whales to return to pre-exploitation levels following their decimation in numbers during the years from approximately 1925-1975.

More (lots more!) 555 page report by The Scientific Committee on Antarctic Research (SCAR);
"The Antarctic Climate Change and the Environment (ACCE) Report"

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