Saturday, 27 February 2016

Arctic warming

Three kinds of warming in 

the Arctic

26 February, 2016
The Arctic is prone to suffer from three kinds of warming. Firstly, the Arctic is hit particularly hard by emissions, as discussed in earlier posts such as this one and this one.

Secondly, warming in the Arctic is accelerating due to feedbacks, as discussed on the feedbacks page. Many such feedbacks are related to decline of the snow and ice cover in the Arctic, which is in turn made worse by emissions such as soot.

Thirdly, the most dangerous feedback is release of methane from the Arctic Ocean seafloor, due to hydrates getting destabilized as heat reaches sediments

Last year, Arctic sea ice reached its maximum extent on February 25, 2015. This year, there's a lot less sea ice in the Arctic than last year. The difference is about 300,000 square km, more than the size of the United Kingdom.
Sea ice can reflect as much as 90% of the sunlight back into space. Once the ice has melted away, however, the water of the ocean reflects only 6% of the incoming solar radiation and absorbs the rest. This is depicted in above image as feedback #1.
As Professor Peter Wadhams once calculated, warming due to Arctic snow and ice loss could more than double the net warming now caused by all emissions by all people of the world.
Professor Peter Wadhams on albedo changes in the Arctic, image from Edge of Extinction
Sea ice acts as a buffer that absorbs heat. When ice is melting, each gram of ice will take 334 Joule of heat to change into water, while the temperature remains at 0° Celsius or 32° Fahrenheit.

Once all ice has turned into water, all further heat goes into heating up the water. To raise the temperature of one gram of water by one degree Celsius then takes only 4.18 Joule of heat. In other words, melting of the ice absorbs 8 times as much heat as it takes to warm up the same mass of water from zero to 10°C. This is depicted in above image as feedback #14.

Above video, created by Stuart Trupp, shows how added heat at first (A) goes mainly into warming up water that contains ice cubes. From about 38 seconds into the movie, all heat starts going into the transformation of the ice cubes into water, while the temperature of the water doesn't rise (B). More than a minute later, as the ice cubes have melted (C), the temperature of the water starts rising rapidly again.

Methane is a further feedback, depicted as feedback #2 on the image further above. As the water of the Arctic Ocean keeps getting warmer, the danger increases that heat will reach the seafloor where it can trigger release of huge amounts of methane, in an additional feedback loop that will make warming in the Arctic accelerate and escalate into runaway warming.

Sediments underneath the Arctic Ocean hold vast amounts of methane. Just one part of the Arctic Ocean alone, the East Siberian Arctic Shelf (ESAS, see map below), holds up to 1700 Gt of methane. A sudden release of just 3% of this amount could add over 50 Gt of methane to the atmosphere, and experts consider such an amount to be 
ready for release at any time.
Total methane burden in the atmosphere now is 5 Gt. The 3 Gt that has been added since the 1750s is responsible for almost half of all global warming.

The amount of carbon stored in hydrates globally was in 1992 estimated to be 10,000 Gt (USGS), while a more recent estimate gives a figure of 63,400 Gt (Klauda & Sandler, 2005). The East Siberian Arctic Shelf (ESAS) alone holds up to 1700 Gt of methane in the form of methane hydrates and free gas contained in sediments, of which 50 Gt is ready for abrupt release at any time.

The situation is dire a calls for comprehensive and effective action as described in the Climate Plan. 
- Arctic sea ice area at record low for time of year

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