Some feedback on feedbacks.

link to sea ice images

Pre-Script: For UMass students, who would like a better understanding of the basic functions of climate, and science of climate change- Prof. Rob DeConto's class, Geo Sci 100, Earth Transformed.  It is a 4 credit course that satisfies science requirements. An excellent class- both thorough and digestable.

Feedbacks- Feedbacks refer to a reaction, or chain of reaction that either amplify, or diminish the original action.  If the reaction amplifies the original impact it is considered a positive feedback, if it diminishes it, it would be considered a negative feedback.

While nature is full of negative feedbacks, where the natural systems balance each other, they have tended to be slower acting.  Of more concern are positive feedbacks where initial warming is amplified.

For example, as the climate warms, the amount of ice in the Arctic is less. Ice is reflective, whereas exposed ocean absorbs more of the sun’s energy, temperatures increase and more Sea Ice melts.  This is a positive feedback loop, even though the results are not helpful.  It is often referred to as the Albedo Effect, or the sea ice feedback.

On the other hand, a warmer climate (perhaps due to Greenhouse gasses) increases water vapor in the atmosphere; this generally increases precipitation and the growth of vegetation. Erosion of exposed rock is sped up, dissolving minerals interact with water and CO2, in a process called chemical weathering.  When the interacting chemicals reach the ocean, sea life is able to bind the combined carbon and minerals into shells, which eventually dissolve and sink.  The carbon is now in long-term storage, a literal Carbon sink.  However, the process is very slow, much slower than our rate of emissions. Nonetheless, Chemical weathering is a good example of negative feedback, sometimes called a thermostat, and an excellent candidate for explaining how the earth recovered from very high carbon atmosphere (2000ppm) on prehistoric earth.

Some other key feedbacks are melting tundra, which releases Methane, a more potent, but shorter-lived Greenhouse gas than carbon. Methane is also stored along the continental shelf, at a depth that holds it in frozen form.  Enough warming would allow these pockets to revert to gas and escape, accelerating warming.

There is some concern that too much melting sea ice would leave a layer of cold water on the surface in arctic regions, because fresh water is less dense than salt water.  If the ocean water were to become too stratified, for the normal mixing to occur, the oceans ability to distribute heat around the globe could be compromised.  It is less clear at what point this might have an effect, but an exaggerated portrayal was the plot for The Day After movie.  The common description is a shut down of the Ocean conveyors.

Clouds can block the suns warmth from entering the lower atmosphere, or they can trap heat at the surface. Clouds present one of the most difficult aspects of climate change to accurately model. Joni was right, we need to look at them from both sides, now. Positive and negative.

So remember, Positive and Negative Feedbacks do not refer to a feedback’s usefulness to humanity.  A positive feedback amplifies the original heating or cooling action.  A negative feedback counter balances, or diminishes the original effect.