Arctic Sea Ice-Hot Topic.

There may be some truth to the theory of global warming,but are the ice caps really melting in the manner described in the press?


Antarctica's is a landmass covered almost entirely in ice (98%) and it is surrounded by sea ice.This is a significant difference to the North Pole which is located in the middle of the Arctic Ocean,amidst waters that are almost permanently covered with constantly shifting sea ice.

As the Antarctica has bedrock beneath the ice,most of it has proven largely impervious to climate change and its deep interior is actually growing in volume.
In contrast the outer edges of the continent have had several ice break off over the years,but the amount of sea ice has remained stable,and in some places even increased over the past 30 years.








The North pole,or the Arctic Ocean,has a temperature surface that is fairly constant;near the freezing point of seawater,and there is considerable seasonal variation in how much pack ice of the Arctic ice pack covers the Arctic.In the winter the relatively warm ocean water exerts a moderating influence, even when covered by ice.This is one reason why the Arctic does not experience the extremes of temperature seen on the Antarctic continent.

Some sea ice is permanent, persisting from year to year,and some is seasonal,melting and refreezing from season to season.Because the extent of the sea ice is important both for the Arctic marine ecology and for the role it plays in the Earth's climate, understanding the variation of this extent during the year and from year-to-year is vital.Each year,the minimum sea ice extent in the northern hemisphere occurs at the end of summer,in September.By comparing the extent of the sea ice in September over many successive years,long term trends in the polar climate can be assessed.

This link shows the yearly minimum sea ice concentration from September for each year from 1979 through 2003.Its clear how the ice increases and decreases on a regular basis.

svs.gsfc.nasa.gov...

This link shows the yearly maximum sea ice concentration from 2003 through 2008.The ice extent appears to change little over the years.

svs.gsfc.nasa.gov...



Today the sea ice at its minimum has been at its lowest extent ever.But,as the sea ice fluctuates so much on a yearly basis,its more than possible that it may increase next year.

The maximum extent must also be taken into account.If global warming was effecting the ice in such a destructive manner you would expect this to be effected too,yet the images clearly show that at certain times of the year this ice still reaches the same extent on a regular basis.

The Arctic sea ice maximum extent has been affected and is below the average value for the recent past.



In this plot the record low year, 2007, for ice extent is seen in green dashes, the current year, 2008 just in case you werent sure, is shown in blue and the average ice extent for 1979-2000 is shown in grey. It is clear that the average line is higher throught the extent of the plot. The maximum ice extent will be around March so isn't covered completely by this graph but the extent at the end of April is shown. (I couldn't find a better plot quickly)

There is inter-annual variabilty in the ice extent, both in the maximum and minimum. This however is natural and to be expected. That is why long term analysis must be done, such as comparing against longer term averages, as shown above.

To really understand the problem with the Arctic ice cover you should look at the average ice thickness.



The above plot shows the age of the ice in the arctic. The left hand one is the average age over 1985-200 and the right shows 2008, both from February. The age of the ice is a proxy for the ice thickness, the older the ice the thicker it is. As can be seen there has been a huge reduction in older, multi-year, ice and a corresponding increase in new first year ice. The new, and thinner ice, takes a lot less energy and time to thaw than the multi-year thick ice. This means that the thawing of ice in the Arctic will take less time each year as instead of having to thaw thick ice it only has to thaw relatively new ice. If the multiyear ice disappears completey then it is reasonable to expect that the Arctic will become ice free in some summers.

Of course new first year ice will reform in the winter wherever it is cold enough and the extent of this cold area has changed only slightly, thus the maximum ice area has been affected much less.

Hopefully I have covered most of your points. Of course the Antarctic is different but here there are areas where the ice thickness is decreasing as well as areas where it is increasing. It is an interesting area that requires a lot more study

reply to post by Iggus


Thanks for your reply,very helpful.

This means that the thawing of ice in the Arctic will take less time each year as instead of having to thaw thick ice it only has to thaw relatively new ice. If the multiyear ice disappears completey then it is reasonable to expect that the Arctic will become ice free in some summers.

Its highly possible.

But couldn't it be also said that it is just park of nature's cycle?

If there have been other ice ages that means the planet has warmed itself and cooled itself all without mankind's help.

You are right that this doesn't show the cause of climate change, it is just a pointer to the existence of climate change.

There have been many changes in climate seen in the paleo-records, with both warmer times and colder times than now. It is not always possible to give reasons why the changes took place although some causes have been suggested, such as for the younger-dryas event. There is a large concensus opinion within climate scientists which says that humans are the cause of this current climate change. Whether anyone believes that it is human induced is up to them but the climate scientific community is convinced and we should remember that.