Antarctica and Global Warming
The Effects of Global Warming
The polar regions are particularly sensitive to small rises in the annual average temperature, they are sometimes referred to as "the canary in the coalmine" in that they show changes long before they can be seen elsewhere in the world. The mean annual air temperature of the Antarctic Peninsula has increased by nearly 3°C in the region in the last 50 years, the only comparable regions are in the Arctic. The temperature of the rest of Antarctica shows indications of rising at a slower rate.
The situation in Antarctica is being assessed constantly and changes that may have already occurred (such as with the WAIS ice sheet - 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. Though 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 or publication.
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.
Summary points of this page:
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 Western Antarctica has also risen by a comparable amount, this is the region attached to the Peninsula and stretches to the Transantarctic Mountains.
The temperature of Eastern Antarctica has risen by a much smaller amount or has remained stable, this is the region on the other side of the Transantarctic Mountains.
There is no unusual significant loss of ice of any kind from the larger 96% of Antarctica that is not the Peninsula.
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.
The extent of annual sea-ice has been changing in
both the Arctic and Antarctic, in both cases it is
explicable in terms of global warming.
What evidence is there from ice?
West Antarctic Ice Sheet (WAIS) - a slow motion collapse
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.
Recently (May 2014) it has been revealed that the WAIS is collapsing, an event that seems to be unstoppable. It will still take a very long time to happen however, several centuries or perhaps up to 1,000 years.
The key area is the 182,000 square km (70,000 sq miles) Thwaites Glacier which is being undercut by warmer water from the Amundsen Sea resulting in its retreat. The water is being driven by changes in wind patterns in this part of Antarctica. The collapse of the Thwaites Glacier alone could lead to a 1.2m (4ft) rise in global se levels, though the biggest effect is likely to come from it acting as an "ice dam" a sort of cork in a bottle of the rest of the WAIS behind it. This could lead to another 3-4m (10-13ft) rise in sea level.
The collapse of the glacier and rise in sea levels is thought to progress slowly for about two hundred years, but then it probably will speed up considerably. It is thought that there may be two stable states for the WAIS, as it is at the moment (or rather as it was about 50 years ago) and then for it not to be there at all, currently it is undergoing a change between the two states. From 1992 to 2011, the Thwaites Glacier retreated around 14 km, faster than anywhere else in Antarctica.
The end result of this is the possibility that we have already been committed to a rise in global sea levels by 3m or more over the coming centuries.
The Larsen B Ice Shelf
Larsen B ice shelf, 31sth Jan 2002 - 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 due to cracks, 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.
Arctic and Antarctic Sea Ice
Seasonal sea-ice, that is ice that forms in the winter and disappears in the summer, in Antarctica and the Arctic are both changing though in opposite directions.
Arctic sea ice trend, 1981-2015:
average decrease of 2.4% per decade
Antarctic sea ice trend, 1979-2015:
average increase of 4.1% per decade
Sea ice can build up and disappear much more quickly than the much thicker glaciers and ice shelves, the average thickness in Antarctica is around 1m, in the Artic it is 2m, glaciers and ice shelves measure in at least 10's of meters and commonly 100's and 1000's. The area of Antarctica approximately doubles each winter due to the formation of sea ice.
The area of Arctic sea ice in April 2015 was the second lowest ever measured, at the same time, the area of Antarctic sea ice in the same month was the highest ever measured (it is measured by satellite). During this time the average temperature in the Weddell Sea was 1-4 °C (2-7°F) above average for the month of April, this was where much of the extra sea ice had formed leading to the record measurement for ice cover.
The reasons for these changes is complex, different areas react in different ways to changing climate, while it may seem intuitive that warmer temperatures mean less ice in Antarctica and not more, it is explicable, in part by the effect of the ozone hole that forms annually over Antarctica.
The depletion of the ozone hole
has caused an overall cooling trend on the Antarctic continent,
this has masked the effects of warming temperatures at a local
level, particularly on the larger part of East Antarctica and
areas away from the peninsula region.
The loss of ozone has also led to increased winds and storms, both in frequency and strength. Winds in the Southern Ocean have been estimated to have increased by 15-20%. It has caused a low pressure system to form in the Amundsen Sea again both with increased frequency and strength. This low pressure sucks cold air from the interior of Antarctic and across the Ross Sea leading to a great increase in the amount of sea-ice forming in this area in recent years. This has been exacerbated by cold fresh melt water from the Pine Island glacier, which less dense than the sea-water below, floats above it freezing more easily than sea water due to it's lower salt content. The result is that a combination of more frequent cold storms and more readily frozen surface sea water leads to more sea ice being formed.
In addition to these factors are the effects of the El Nino Southern Oscillation which makes the situation more complicated leading to the large annual variability of sea ice formation.
The average extent of sea ice in Antarctica over the last five years compared to the 30 year average.
Note, the two graphs are "opposites" as winter and summer are at different times of the year. Note also how more variable sea ice cover is from year to year in the Arctic than the Antarctic.
Prince Gustav Channel
The Prince Gustav Channel is a stretch of sea that is found between the Antarctic Peninsula on its west side and James Ross Island at its east side. It is around 130km (81 miles) long and from 6 to 24 km (4-15 miles) wide. Until 1995 an ice shelf covering around 700 square kilometers (270 square miles) largely filled this channel, by February 1995 this ice shelf had broken up and the channel was open water and navigable once again.
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
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.
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.
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 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.
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 accurately know how the temperatures vary over even the medium term in Antarctica. The 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, It 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.
- A warmer day in most of Antarctica gives a temperature
well below freezing, say -30°C to -20°C
= Nothing much to see.
- A warmer day in the Peninsula takes temperatures from
say -5C to +5C
= Lots of melting and potential ice break up, lots to see.
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 from the interior and cause greater temperature rises to take place further inland. Ice shelves seem to act as "corks" in Antarctic "ice-bottles", 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.
Are there any biological effects of global warming in Antarctica?Plants
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. Deschapsia antarctica, Antarctic hair grass shown in picture right.
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.
Adelie 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. Until the last 20 years or so, Chinstrap penguins (Pygoscelis antarctica) were 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.
More recently however, Gentoo penguins (Pygoscelis papua) have started to replace both Adelie and Chinstrap penguins and now nest on the Peninsula. Studies of the bones and remains found in abandoned colonies indicates that prior to 1950, no Gentoo penguins nested in these sites at all.
Losers - Adelie
and Chinstrap penguins
Winners - Gentoo penguins
On the other side of Antarctica, the Ross Sea region and East Antarctica, Adelie penguin colonies have remained stable or even increased.
Studies 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 numbers in this region 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.
Picture credits, copyright pictures used by permission: Arctic and Antarctic sea ice, images and graphs - National Snow and Ice Data Center, University of Colorado, Boulder, Colorado. / Deschampsia antarctica - Lomvi2, used under Creative Commons 3.0 Share and Share Alike Unported license. / Ice core - Emily Stone, NSF / Satellite images - NASA
More (lots more!) 555 page report by The Scientific Committee on Antarctic Research (SCAR); "The Antarctic Climate Change and the Environment (ACCE) Report"