mechanism

This is a February 28, 2015, version of the blog page 'The Mechanism', meanwhile updated here
What is the mechanism behind accelerated warming of the Arctic Ocean, huge abrupt methane eruptions from the seafloor of the Arctic Ocean and skyrocketing temperatures?



1. Potential for Methane Release in Arctic

Vast amounts of methane are stored in hydrates under the seafloor of the Arctic Ocean. Furthermore, vast amounts of methane in the form of free gas are contained in sediments under the seafloor of the Arctic Ocean. Thirdly, vast amounts of carbon are frozen in the permafrost and much may enter the atmosphere in the form of methane as the permafrost continues to thaw.

Natalia Shakhova et al. in 2010 estimated the accumulated potential for the East Siberian Arctic Shelf (ESAS) region alone (image on the right) as follows:
- organic carbon in permafrost of about 500 Gt
- about 1000 Gt in hydrate deposits
- about 700 Gt in free gas beneath the gas hydrate stability zone.

In early 2014, Sam Carana estimated annual methane emissions from hydrates and permafrost at 100 Tg (i.e. 0.1 Gt). This methane will contribute to further warming of the air over the Arctic and the North Atlantic, causing further extreme weather events, such as heatwaves and storms along the path of the Gulf Stream from the North Atlantic into the Arctic Ocean, in turn triggering further releases from hydrates at the seafloor of the Arctic Ocean and threatening to escalate into runaway global warming.

[ See: How much time is there left to act? ]
Such methane eruptions are caused by warming water of the Arctic Ocean, which in turn is due to emissions by people. Some elements of the mechanism causing methane to erupt from the seafloor are described in more detail below.

2. Ocean Heat

Ocean temperature anomalies on the Northern Hemisphere for March 2015 were the highest on record. In many ways, the situation looks set to get worse. For the 12-month period from April to March, data from 1880 contain a trendline that points at a rise of 2 degrees Celsius by the year 2032, as illustrated by the image below.

[ click on image to enlarge, from: The Great Unraveling ]
The rise in Northern Hemisphere ocean temperatures was especially profound in September and October 2014, when methane started to erupt from the Arctic Ocean seafloor in huge quantities.
[ click on image to enlarge, from: Ocean Temperature Rise continues ]

Above graph shows a polynomial trendline pointing at an October Northern Hemisphere sea surface temperature anomaly rise of more than 5°C (9°F) by 2050, compared to the 20th century average.

Waters at greater depth are also warming rapidly, as illustrated by the image on the right, from an earlier post, showing a rise in ocean heat up to 2000 m deep that has more than doubled over the past decade. Data from 2005 through to 2014 contain a polynomial trendline that points at a similar rise by 2017, followed by an even steeper rise.

The North Atlantic is warming rapidly, with sea surface temperature anomalies as high as a 12°C (21.6°F) recorded east of North America earlier this year, as illustrated by the image below.

A warmer North Atlantic is a major contributor to the rapidly warming waters of the Arctic Ocean, since the Gulf Stream keeps carrying warmer water into the Arctic Ocean all year long.

A further contributor is a warmer North Pacific.

Further contributions come from the combined impact of numerous feedbacks, in particular changing winds and currents, cryosphere changes and methane releases, as further described below.

On April 11, 2015, a sea surface temperature of 22.2°C (71.96°F) was recorded off the North American coast (green circle bottom), a 12.6°C (22.68°F) anomaly (green circle top).

[ click on image to enlarge, from: The Great Unraveling ]
Ocean heat is carried by the Gulf Stream from the North Atlantic into the Arctic Ocean. The huge amounts of energy entering the oceans translate into higher temperatures of the water and of the air over the water, as well as higher waves and stronger winds.


Above image shows that on September 1, 2014, a sea surface temperature of 17.5°C (63.5°F) was recorded at a location near Svalbard (green circle, co-ordinates in the black panel on the left), a 11.9°C (21.42°F) anomaly. As the bottom part of above image shows, sea surface temperatures around that location were substantially colder, indicating that the 17.5°C surface temperature was caused by ocean heat reaching that location from underneath the sea surface. In other words, subsurface temperatures of the water carried along by the Gulf Stream can be substantially higher than temperatures at the surface, all the way from the coast of North America to the Arctic Ocean. 


3. Feedbacks: Changing Winds and Currents, Cryosphere Changes and Methane

- Changing Winds and Currents

Emissions by people are not only causing temperatures of the atmosphere and oceans to rise, they are also causing winds and ocean currents to change. Such changes can in turn result in heatwaves that are more intense and that persist for prolonged periods. Furthermore, strong northbound winds, combined with strong precipitation and waves can speed up the volume of warm water carried by Gulf Stream into the Arctic Ocean, as discussed in the post Watch where the wind blows. The image below shows waves higher than 10 m (33 ft) near Svalbard close to the edge of the sea ice on March 16, 2015 (green circle).

[ click on image to enlarge, from: Strong Winds And Waves Batter Arctic Sea Ice ]
- Cryosphere changes

A warming atmosphere, warming oceans and decline of the Arctic snow and ice cover all go hand in hand. While the IPCC concluded in AR5 that, for RCP8.5, the Arctic Ocean will likely be nearly ice-free in September before mid-century, Professor Peter Wadhams warned, back in 2012, that the Arctic Ocean could be virtually ice-free within a few years.

Sunlight that previously went into melting the sea ice, as well as sunlight that was previously reflected back into space by sea ice, would be absorbed by the Arctic Ocean instead. In other words, we can expect massive warming. In the above post, Prof. Peter Wadhams warned that warming due to Arctic snow and ice loss may well exceed 2 W per square m, i.e. it could more than double the net warming causing by all emissions by all people of the world.

Professor Peter Wadhams on albedo changes in the Arctic
An exponential trendline based on sea ice volume observations shows that sea ice looks set to disappear in 2019, while disappearance in 2015 is within the margins of a 5% confidence interval, reflecting natural variability, as discussed at the FAQ page.


Rising temperatures are causing the surface of Greenland to change, also resulting in albedo changes.

Thawing of the permafrost will similarly result in albedo changes, while much of the carbon that is contained in the permafrost can be expected to be released in the form of methane or carbon dioxide as the permafrost continues to thaw. The image below pictures permafrost decline as foreseen by the IPCC in AR5. 


Obviously, more rapid decline of the sea ice, and more melting on Greenland and thawing of permafrost will come with albedo changes that will in turn make the permafrost decline more strongly and more rapidly than the IPCC foresees, while this will also cause more rapid temperature rises in the Arctic and even more extreme weather events. One of the dangers is that huge amounts of warmer water will flow from rivers into the Arctic Ocean, as discussed below.

- Warmer Water From Rivers

More sunlight getting absorbed in the Arctic will accelerate warming of the Arctic Ocean directly, while there will also be warmer water flowing into the Arctic Ocean from rivers in Siberia and North America, fueled by stronger and longer heatwaves, storms and wildfires. 

map from: http://en.wikipedia.org/wiki/File:Rs-map.png
Above map shows that a number of large rivers in Siberia end up in the Arctic Ocean. Another large river is the Mackenzie River, which ends in the Beaufort Sea, north of Alaska, where sea surface temperatures of about 20°C (68°F) were recorded in 2013, as the image below illustrates.


Another area of concern, marked by the bottom purple oval in the image below, is located in the north of Canada.


More extreme weather events include heat waves, storms, floods and wildfires, all of which can contribute to more rapid warming of the Arctic Ocean.

The combined effect of all the above will be that methane that is now contained in the form of free gas and hydrates in sediments under the Arctic Ocean, can be expected to be increasingly released as the Arctic Ocean warms further.

- Methane 

Of the vast amounts of methane stored in the Arctic, much of it is prone to be released with further temperature rises, as discussed in this earlier post and in this earlier post. Cracks in sediments used to be filled with ice. Warmer water is now melting the ice that used to sit in cracks. This ice has until now acted as a glue, holding the sediment together. Moreover, the ice in the cracks has until now acted as a barrier, a seal, that prevented the methane contained in those sediments from escaping. In a video interview with Nick Breeze, Natalia Shakhova mentions a sample of sediment taken from the ESAS seafloor in 2011 that turned out to be ice-free to a depth of 53 m at water temperatures varying from -0.6˚C to -1.3˚C. Back in 2008, Natalia Shakhova et al. considered release of up to 50 Gt of predicted amount of hydrate storage as highly possible for abrupt release at any time.

Conclusion from a paper presented at the 2008 EGU conference, on background
of a frame from a video interview by Nick Breeze with Natalia Shakhova.
The image below shows exponential rise based on data of East Siberian Arctic Shelf (ESAS) releases alone, as discussed in the post Quantifying Arctic Methane.


Non-linear rise in methane levels can be expected given that methane's lifetime increases as more methane enters the atmosphere. As the image below shows, methane levels as high as 2845 parts per billion (ppb) were recorded on April 25, 2015. The average daily peak in early 2015 was 2372 ppb, while the highest daily mean ranged from 1807 ppb (January 10) to 1829 ppb (April 22). Daily peaks and daily highest mean levels in 2015 are shown on the image below.


Things look set to get worse. As shown by the image below, from an earlier post, global methane levels have risen sharply from a low of 723 ppb in 1755. Mean methane levels were as high as 1839 ppb in 2014. That's a rise of more than 254%.
The image below, based on data from the IPCC and the World Metereological Organization (WMO), with an added observation from a NOAA MetOp satellite image, further illustrates the recent rise of methane levels and the threat that methane levels will continue to rise rapidly.


When looked at from a longer range of years, above image fits in the black square on the image below.


All these feedbacks can interact and amplify each other in non-linear ways, resulting in rapid and intense temperature rises, as illustrated by the image below.

[ Diagram of Doom, from: Near-Term Human Extinction - for more background, also see Feedbacks ]

4. Collapse of Civilization

As discussed back in 2011, much of the soot from firestorms in Siberia could settle on the ice in the Himalaya Tibetan plateau, melting the glaciers there and causing short-term flooding followed by rapid decrease of the flow of ten of Asia’s largest river systems that originate there, with more than a billion people’s livelihoods depending on the continued flow of this water.

The threat is that such rapid temperature rises will appear at first in hotspots over the Arctic and eventually around the globe, while also resulting in huge temperature swings that could result in further crop loss and depletion of supply of food and fresh water. As discussed in the 2007 post Ten Dangers of Global Warming, food supply could come under threat worldwide, with much industrial activity coming to a halt. 

Less industrial activity will not cause an immediate fall of temperatures, though. Instead, it would make that the aerosols that are currently sent up in the air by such activities and that are currently masking the full wrath of global warming, will fall out of the air in a matter of weeks. Until now, about half of the global temperature rise is suppressed by such aerosols. Stopping aerosols release overnight could make temperatures rise abruptly by 1.2°C (2.16°F) in a matter of weeks.

[ from: 2015 without Arctic sea ice ] 
5. Runaway Global Warming

Rapidly rising temperatures will cause stronger evaporation of sea water. Since water vapor is one of the strongest greenhouse gases, this can further contribute to the non-linear temperature rises pictured below.
[ click on image to enlarge, from: Methane Levels Early 2015 ]
In conclusion, the situation is dire and calls for comprehensive and effective action, as discussed at the Climate Plan page.

An earlier version of 'The Mechanism' was posted at the Arctic-news blog on February 28, 2015.



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