CLIMATE WATCH - Arctic Sea Ice

 

From https://nsidc.org/arcticseaicenews/

Arctic sea ice area changes with the seasons, but there is a long-term decline*, caused by global warming.

Most scientific sources suggest there might be a few days of "ice-free" conditions in the Arctic Ocean one summer around mid-century. Ice-free sea (being darker) absorbs heat, while ice reflects heat.

Progressively over time, more "ice-free" days are likely, on average. 

But what exactly does an "ice-free Arctic Ocean" mean?

For measurement purposes, researchers divide the ocean up into small cells.

The data cells are 25 km by 25 km.

If there is more than 15% ice on a cell, it counts as an "ice-covered" cell.

If there is less than 15% ice on a cell, it counts as "ice-free".

At some time, the Arctic Ocean one September will meet the 'ice-free' criterion - each cell will be counted as ice-free as long as there is less than 15% ice in the cell.

But an 'ice-free' Arctic Ocean will still have some areas with up to 15% ice cover.

(15% or less may have been chosen as "ice-free" at some point because at that concentration you can pass through without an icebreaker - over 15% you need a ship set up as an icebreaker)

It's worth noting that cells with as little as 16% ice are counted as 'ice-covered' in this system.

*Arctic sea ice graph for the last 1450 years:

    

The graph was produced from data in this paper - Kinnard et al, 2011....

http://www.nature.com/nature/journal/v479/n7374/full/nature10581.html




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