For years now, scientists have warned that additional atmospheric heat caused by human releases of carbon dioxide (CO2) could result in amplifying feedbacks that cause even more heat. At first, most of these comments were academic, an exercise in predicting what would happen if humans did not curtail greenhouse gas emissions. But as human CO2 emissions continued to increase, global warming amplified and changes accelerated. Now the warnings from scientists are much more direct. Consider NASA scientist James Hansen’s most recent statement:
“We don’t have a substantial cushion between today’s climate and dangerous warming. Earth is poised to experience strong amplifying feedbacks in response to moderate additional global warming.” – James Hansen
Amplifying Feedbacks via Microphone
An amplifying feedback is a rapidly increasing response to an initial forcing. In everyday life, people are generally familiar with what happens when you put a microphone close to a speaker. The microphone picks up ambient noise, and pushes it out through the speaker. This, now louder, noise is picked up again by the microphone and sent back to the speaker as a much louder input. The loop continues until the speaker is pouring out a rapidly rising wail of sound.
Arctic Sea Ice Melt as Amplifying Feedback
In nature, something very similar can happen as a result of an initial climate forcing. In the Arctic, we can see this in the form of sea ice melt over the past few decades. Increases in ocean temperature and stored heat has gradually worn away at both Arctic sea ice area and Arctic sea ice volume.
In 2007, Arctic sea ice area reached the lowest levels ever recorded, a level far below the 1979-2001 average. Sea ice lost area equal to 20% of the total summer coverage of the previous year. More than 20% of Arctic sea ice gone in one year. Since that time, Arctic sea ice area has failed to recover with 2011 showing the second lowest area on record at end of summer, an area very close to the unprecedented 2007 record low.
The above image shows the difference between 1980 and 2007 Arctic sea ice (Source: Cryosphere Today).
But sea ice area as seen from above only tells half the story. The second half is told by total sea ice volume. Area measures how much surface is covered by ice. Volume measures the total amount of ice by taking into account sea ice thickness. And when looking at volume, there has been a precipitous and unrelenting fall.
Sea Ice Volume shown above is calculated using data from the Pan-Arctic Ice Ocean Modeling and Assimilation System of the Applied Physics Lab at the Polar Science Center and inserting it into a curve fitting process. And the curve shows a near-ice free Arctic under current trends by or before the summer of 2020. In fact, the model shows that September could see ice-free seas as early as 2013. Not likely, but another couple summers like 2007 could bring us very close.
But even if current trends don’t hold, additional statistical analysis shows nearly ice free summers by or before 2035.
And the, usually guarded, IPCC findings point toward ice-free summers before 2050. So depending on the dynamics of Arctic weather, which can certainly be very dynamic, our best analysis points toward a continuation of rapid collapse or a shift to a more gradual melt down.
Regardless of final melt dates, APL sea ice volume measurements show Arctic sea ice is getting very, very thin.
The reason Arctic sea ice melt is an amplifying feedback is due to the heat reflective nature of ice vs the heat absorption nature of water. Water just by virtue of color alone, absorbs more sunlight than ice. This results in water temperature in ice free seas being as much as 5 degrees C warmer than water beneath sea ice. And this warmer water heats both the air and the entire water column. Loss of sea ice alone is a powerful amplifier of temperatures during the Arctic summer and this extra absorbed heat is on top of the extra heat added by human caused global warming via CO2 emissions.
Arctic Methane Releases as Amplifying Feedback
It is the nature of single amplifying feedbacks that they tend to kick off other feedbacks. And this is exactly what is happening with Arctic methane.
In the Arctic, both methane and ice have been locked together in a chilly marriage ever since the roof of the world began to freeze about 10 million years ago. The reason for this is that the bodies of dead plants and animals have accumulated in the tundra’s frozen soil year after year. Dead and decayed biological matter has also been locked in formations called methane hydrates in the shallow Arctic sea.
When the ice melts, seas warm. This results in warmer winds blowing over the tundra. The tundra’s permfrost soils begin to melt and, when they do, bacteria begin to break down the dead matter locked in these frozen soils for so long. Once the matter breaks down, methane is released.
Now methane is a very powerful greenhouse gas — packing a potency twenty times that of CO2. So Arctic methane releases result in a powerful global warming force adding to the effects of sea ice melt and human CO2 emissions. The result is that the Arctic warms even more, more tundra melts, and more methane is released.
Often, when heat melts the tundra, new lakes form. These lakes contain large volumes of methane. Sometimes, researchers ignite this methane to demonstrate how much is being emitted from the lakes. Often, these ignitions result in dramatic plumes of fire, illustrating the explosive nature of methane emissions in the Arctic.
But, sometimes, this new methane seeping up from Arctic soils are ignited by nature in the form of lightning strikes. And these lightning strikes can result in vast tundra fires that burn massive swaths of the Arctic. One such tundra fire recently burned an area the size of Cape Cod in Alaska.
These tundra fires convert massive volumes of biological matter into CO2 which adds another amplifying feedback.
Out Gassing of Submerged Arctic Methane
Even though vast areas of land are now providing amplifying feedbacks as Arctic tundra thaws, some of the thawing tundra isn’t on land, it’s under the water. North of Siberia, the East Siberian Arctic Shelf (ESAS) is a protrusion of tundra now flooded by the Arctic Ocean. As the water above this shallow shelf warmed, the submerged tundra began to thaw, and as it thawed it began to release methane.
These underwater methane releases were only recently discovered. Since their discovery, the rate of methane release has defied all expectations, pouring more methane into the atmosphere than any other natural source. Just this summer, Arctic researchers including Igor Semiletov discovered enormous plumes of methane venting up from the sea bed. According to the researchers, some of these methane plumes were more than 1 kilometer across.
“Earlier we found torch-like structures like this but they were only tens of metres in diameter. This is the first time that we’ve found continuous, powerful and impressive seeping structures, more than 1,000 metres in diameter. It’s amazing,” Dr Semiletov said in a 2011 interview. “I was most impressed by the sheer scale and high density of the plumes. Over a relatively small area we found more than 100, but over a wider area there should be thousands of them.”
Some of this submerged methane comes from the decomposition of submerged tundra, the rest comes in the form of destabilized methane hydrates. As seen on the map below, the ESAS is just one of many areas where high concentrations of methane hydrate are expected.
Overall, 1700 gigatons of carbon are estimated to be locked up in the melting tundra and more than 4400 gigatons of carbon are estimated to be stored in the form of methane hydrates. By comparison, remaining conventional fossil fuel sources are estimated to contain about 1100 gigatons of carbon — about equal to the amount already emitted. So even if a fraction of Arctic Methane destabilizes it could more than double the impacts of human caused climate change.
But there is additional danger. They include loss of oxygen in the world’s oceans, rapidly increasing ocean acidification, the risk of much larger tundra fires, and the risk of very large fires sparked by lightning strikes in the event of sudden, large methane releases. These dangers should be seen as directly related to the risk posed by amplifying feedbacks.
Combined Impacts
When added to the very high volumes of CO2 produced by human activity, a volume 150 times that produced yearly by volcanoes, the increased heating caused by melting sea ice and increased methane release creates a dangerous amplifying feedback to global warming. The effects of these feedbacks are large and growing larger. The valid concern among scientists and those researching climate change is that these feedbacks will only expand exponentially as human forcing increases, eventually creating a cascade of effects whose scale is beyond the ability of humans to reign in.
Sources:
Cryosphere Today: http://arctic.atmos.uiuc.edu/cryosphere/
National Snow and Ice Data Center: http://nsidc.org/arcticseaicenews/
The Polar Science Center: http://psc.apl.washington.edu/wordpress/research/projects/arctic-sea-ice-volume-anomaly/
“Vast Plumes of Methane Seen in Arctic as Sea Ice Retreats” http://www.independent.co.uk/news/science/vast-methane-plumes-seen-in-arctic-ocean-as-sea-ice-retreats-6276278.html
International Arctic Research Center: http://www.iarc.uaf.edu/en/about
The Storms of My Grandchildren by James Hansen, 2008
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