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




Popular posts from this blog

Climate Change - The link with mass extinctions

Image
What is the worst-case scenario for climate change? The geological record shows that when the atmosphere suddenly changes, there are big effects on living things. Five major  mass extinction  events are recorded in the rock record of the last 600 million years. The biggest extinction was at the end of the  Permian , around 252 million years ago. It is called the  End-Permian mass extinction. Only about 8% of species survived to live on in the Triassic Period. This photo shows geologists investigating tilted sedimentary rocks at Shangsi in South China. Triassic rocks (at the top right) lie over the older Permian rocks. Each mass extinction in the rocks matches with a change in the chemistry of the rocks called a ' carbon excursion '. Some of the carbon excursions are 'negative CEs' and some are 'positive CEs'. Negative CEs  indicate that lots of gaseous carbon compounds escaped into the air, causing warming. These are sometime
Read more

Climate Change - The Greenhouse Effect

Image
What do scientists mean by the " Greenhouse Effect "? When the Sun's energy arrives at the Earth, it travels through the air. Some is reflected back to space, but some hits the Earth and warms it. The warm Earth gives off  infrared radiation  with various wavelengths.   Some of those waves can pass back out of the air to space, but some are absorbed by certain gases in the air. The gases then re-emit the energy into the air. If there are more of those gases, less heat escapes into space. An extreme case has happened on Venus. Concentrated  'greenhouse gases'  on Venus have caused the surface temperature to rise to 735  Kelvin  (462 degrees C; around 900 degrees F) Carbon dioxide levels in the atmosphere have risen quickly  since people began burning large quantities of fossil fuels. There was carbon dioxide in the air before that, at around 270 parts per million. Without any carbon dioxide, the Earth would be very cold.
Read more

Climate Change - Coal and carbon dioxide

Image
Coal, oil and natural gas are  fossil fuels . When they are burned, they  change the Earth's atmosphere. How is that possible?       C oal  is a good example. Coal was formed  hundreds of millions of years ago . Geologists say that a three-metre (10-foot) coal seam took between  12,000 and 60,000 years  to form . Ancient trees and other plants lived, died and were fossilised. All those plants took  carbon dioxide  out of the atmosphere.  Some larger coal seams are, for example, 10 metres thick. They took around  40,000 years to form,  but have been mined and burned in a little over  100 years. The fastest rise of CO 2  in the air seen in   the ice core record (800,000 years)  is  20 ppm in 1000 years. The CO 2  level in the atmosphere is now rising at around  20 ppm per decade . The  carbon  joins up with  oxygen  when it burns. Each carbon atom joins with two oxygen atoms to make a  carbon dioxide molecule .  As a result, oxygen concentration i
Read more