In my first posting we discussed how greenhouse gases like carbon dioxide reflect low energy radiation back to the surface of the planet which helps the planet maintain a stable temperature. My second posting discussed how the carbon cycle regulates the atmospheric level of carbon dioxide. That posting also discussed how the burning of fossil fuel disrupts the carbon cycle which increases the atmospheric level of carbon dioxide which created and enhances current global warming. Recently scientists have been shocked by how fast sea-ice is melting in the Arctic which suggests an atypical, nonlinear relationship between greenhouse gases and global warming because some other factor must be amplifying the warming. This factor is the feedback phenomena.
Different parts of the climate system interact through feedback factors that amplify or diminish the forces that change the climate. There are two types of feedback factors: positive and negative. Forces that amplify climate change are positive feedback factors while forces that diminish climate change are negative feedback factors. This posting will discuss the effect the accelerated melting of sea-ice in the Arctic Ocean has on the climate. My next posting will discuss other feedback factors.
Light covered surfaces such as ice and snow reflect the incoming solar radiation back into outer space while dark covered surfaces such as oceans and land not covered with ice or snow absorb the incoming radiation which creates heat and warms the planet. The increase in global temperature due to the release of carbon dioxide from the burning of fossil fuel triggers the melting of Arctic sea-ice. As the sea-ice melts there is less ice to reflect the incoming solar radiation and more open ocean to absorb the solar energy. This absorbed energy triggers a positive feedback that warms the ocean and overlying atmosphere which in turn causes more ice to melt and thus more warming that initiates a cascade of effects. The warm water over the Arctic spreads and destabilizes the Greenland ice sheet. In 2008 the Northwest Passage was ice free for the first time in history. Between 2003 and 2008 the Greenland ice sheet lost an area 10 times the size of Manhattan and this past 2010 summer a 100 square mile island of ice (four times the size of Manhattan) broke off the Greenland ice sheet.
Methane is a greenhouse gas that is 24 times stronger than carbon dioxide. Methane is stored on the ocean floor as crystals and is stable when cold an under pressure. Some estimates suggest that there is more methane on the ocean floor than in all the fossil fuel reservoirs. As the Arctic Ocean warms, it releases methane. In 2010 scientists reported rising methane plumes in the Arctic Ocean shelf off Siberia.
As the atmosphere warms over Arctic Ocean and spreads over land, it triggers melting of the permafrost which releases methane by decomposing previously frozen vegetation. Twenty five per cent of North America is covered by permafrost and this frost can be up to 4900 feet thick.
Clearly, the burning of fossil fuel releases significant amounts of carbon dioxide into the atmosphere. This release triggers a positive feedback system which accelerates the melting of sea-ice and glaciers. The melting of Greenland glaciers along with Antarctic glaciers will increase the mean sea level. In the previous 3000 years the sea level rose only 0.4 to 0.8 inches but in the 20th Century it rose 6-8 inches.
This feedback factor also releases methane from the ocean floor and the permafrost. This release of methane along with the continued release of carbon dioxide from burning of fossil fuel could initiate a “runaway greenhouse” and increase the probability that the planet will reach a tipping point where the current gradual rise in global temperature will be replaced by an abrupt and significant increase in global temperature. If we stop burning fossil fuels by converting to renewable energy sources, past geological history suggests that the planet will recover but it will take centuries! This history also suggests that there will be massive species extinction. In this scenario the fate of humans is not known. At the very least there will be fewer of us around.