The Arctic and Antarctic.
The Arctic and Antarctic poles are totally different in geographic properties and although both are melting they are doing so in different ways and understanding the geophysical differences and what is happening is vital to analysing where the threats are.
In its simplest form the Arctic is an ocean surrounded by land and the Antarctic is a land mass surrounded by sea.
The Arctic ice is already floating in the sea and so its melting will not add to sea levels but Greenland is nearby and the ice there is capable of raising sea levels seven meters. Antarctica's ice is capable of raising sea levels sixty metres if it melted.
Just one metre of sea level rise would bring economic and human disaster to the world, so there is a great deal of sensitivity and immediacy to these large numbers.
In its simplest form the Arctic is an ocean surrounded by land and the Antarctic is a land mass surrounded by sea.
The Arctic ice is already floating in the sea and so its melting will not add to sea levels but Greenland is nearby and the ice there is capable of raising sea levels seven meters. Antarctica's ice is capable of raising sea levels sixty metres if it melted.
Just one metre of sea level rise would bring economic and human disaster to the world, so there is a great deal of sensitivity and immediacy to these large numbers.
The Arctic ice is melting quickly because the Poles warm considerably faster than the rest of the planet and as the ice disappears its highly reflective white surface is replaced by dark blue ocean water that absorbs the sun's heat and warms the sea water. As the ice flows break up the currents carry them down the coast of Greenland, through the Fram strait, where they go into the Atlantic and then melt completely. The Pacific ocean is about one metre higher than the Atlantic and so the current flows that way.
The Arctic ice was fourteen million square kilometres at the start of the industrial age (1880) and has been reduced to three and a half million square kilometers recently and it is in a death spiral.
There three big issues with the warming of the North pole of which one is the release of methane from the melting permafrost and also from methane clathrates which are frozen methane held on the sea bed by cold and pressure. Methane is greenhouse gas 80 times more powerful than CO2 over ten years and there are billions of tonnes of it currently frozen in place and it is being released. Some people think that this is the biggest threat to the planet.
The second concern is the speed at which Greenland's ice is melting. Greenland is at a lower latitude and even though it's plateau is 3000 metres high it is subject to more warmth. It is also at the latitude of industrial activity and its surface is being covered with soot and the dark colour absorbs heat quickly and aids melting. Greenland's glaciers meet the sea in deep fiords and so present a relatively short front to the sea, but warm sea water is getting under the glaciers in the fiords and melting the ice from below and as they melt the speed of the land based ice is accelerating and the ice is slipping into the sea.
Greenland is melting at the rate of about two hundred and fifty gigatonnes of ice a year (A gigatonne is a cube one kilometre down each face) and this represents about one millimetre of sea level rise each year. It may not sound much but it is a relentless addition and it is accelerating.
The effect of the melting sea ice on the weather is dealt with here.
Greenland is melting at the rate of about two hundred and fifty gigatonnes of ice a year (A gigatonne is a cube one kilometre down each face) and this represents about one millimetre of sea level rise each year. It may not sound much but it is a relentless addition and it is accelerating.
The effect of the melting sea ice on the weather is dealt with here.
The third issue is to do with the Gulf stream which is an important part of a global system of ocean currents which distribute heat and nutrients from the equatorial regions to the Poles and back to the tropics again. Most of the system is driven by the winds but an important part is where the warm water from the Caribbean travels north and as it flows along it is evaporating moisture and becoming more salty as it goes and also cooler. When it gets to the Arctic it freezes and the fresh water becomes ice and leaves the salt behind. This makes the remaining sea water very salt laden and heavy and it sinks to the ocean floor and starts a journey to the Antarctic, which might take two hundred years.
The big danger is that, as the fresh water floods out of Greenland, it will dilute the saltiness of the Gulf stream so that when it gets to the Arctic it will not sink and this will stall the complete system.
This is a big danger to Europe as it is currently much warmer than it's high latitude would indicate and if the Gulf stream stopped the temperature would drop several degrees, plunging farming and food production into chaos plus a whole host of associated problems. There is already a permanent cold patch just southeast of Greenland and the Gulf stream has slowed down but fortunately speeded up again which is causing concern.
The big danger is that, as the fresh water floods out of Greenland, it will dilute the saltiness of the Gulf stream so that when it gets to the Arctic it will not sink and this will stall the complete system.
This is a big danger to Europe as it is currently much warmer than it's high latitude would indicate and if the Gulf stream stopped the temperature would drop several degrees, plunging farming and food production into chaos plus a whole host of associated problems. There is already a permanent cold patch just southeast of Greenland and the Gulf stream has slowed down but fortunately speeded up again which is causing concern.
The Antarctic is a completely different situation as it is a large, high, continent surrounded by the Southern ocean. In addition to this Antarctica is divided into two parts, East and West Antarctica, separated by the Transantarctic Mountains . West Antarctica is the smaller area and consists of a mass of permanent thick ice, resting on the sea bed and held in place by a chain of islands. East Antarctica is mostly solid land and the ice has an altitude of about 3000 metres (10,000 feet) with a series of glaciers round the edge which feed into the sea.
Although Antarctica is warming quickly the high altitude of East Antarctica keeps it well below freezing and also, the loss of Ozone, which is a greenhouse gas, reduces the full extent of warming.
If snow falls in East Antarctica it is unlikely to melt and any loss is due to a steady slide of the glaciers into the sea where it forms an ice shelf and spreads out to sea before breaking into icebergs in a natural way.
Although Antarctica is warming quickly the high altitude of East Antarctica keeps it well below freezing and also, the loss of Ozone, which is a greenhouse gas, reduces the full extent of warming.
If snow falls in East Antarctica it is unlikely to melt and any loss is due to a steady slide of the glaciers into the sea where it forms an ice shelf and spreads out to sea before breaking into icebergs in a natural way.
West Antarctica consists of a massive ice shelf resting on the ocean floor and held in place by a series of islands is also at a warmer latitude and so is much more sensitive to warming from the atmosphere, although this is not where the main threats are coming from.
Because the high centre of Antarctica remains exceptionally cold and the warmer equatorial regions are warming up there is an increasing differential in temperature between the two areas and this has led to an increase in the speed and strength of the winds around the Southern ocean. This has the effect of speeding up the Southern ocean currents and stirring up the deeper warmer water and brings the deeper warmer water closer to the surface.
Souther ocean water temperature is relative because sea water freezes at -2C and so it is either solid ice or just above that temperature and this cold water extends down to about 600 metres. The deep ocean bottom water is also cold, but at about +2C. As the surface currents have become stronger they are bringing this +2C water closer to the surface and it is now touching the bottom of the huge ice shelves and melting them from below.
Water will conduct heat (or cold) many times faster than air and so the melting process is massive even at relatively close temperatures and the ice is melting from the bottom at the rate of tens of metres a year.
Water will conduct heat (or cold) many times faster than air and so the melting process is massive even at relatively close temperatures and the ice is melting from the bottom at the rate of tens of metres a year.
As the ice shelf becomes thinner it is more prone to breaking up and several ice shelves are in a precarious state. Larsen 'A' and 'B' have disintegrated and Larsen 'C' has a huge crack in it (June 2017) and we are watching to see what happens. Pine Island and Thwaites ice shelves are under threat.
Larsen 'C' is the fourth largest ice shelf in Antarctica and Pine Island and Thwaites ice shelves are holding back massive amounts of land ice that could raise sea levels by five metres.
Larsen 'C' is the fourth largest ice shelf in Antarctica and Pine Island and Thwaites ice shelves are holding back massive amounts of land ice that could raise sea levels by five metres.
In summary the ice in the Polar regions is melting rapidly and have the potential to raise sea levels by sixty five metres but we only need one metre to displace hundreds of millions of people and flood trillions of dollars of infrastructure. The wealthy countries will be particularly hard hit and the sea level is likely to rise two metres this century.