Feedbacks in Climate

One of the many complexities of the climate system is the behavior of positive or self-reinforcing feedbacks.  Positive feedbacks, in the context of climate change, are cycles that once triggered, build on themselves and cause a large warming.  Of the most significant feedbacks are the ones associated with ice, permafrost, and water vapor.  These three positive feedbacks are well-known; however they have yet to be incorporated into most climate models.  What this correlates to is an underestimate of the warming that will occur as a result of a certain concentration of greenhouse gases.  IPCC’s (Intergovernmental Panel on Climate Change) Fifth Assessment Report should include most of these feedbacks.

  • Ice: The feedback associated with ice is very simple.  As the Earth warms, reflective ice and snow melt and uncover dark water and land.  These darker surfaces absorb more solar radiation than the ice and lead to more warming.  On a global scale, this process means a decrease in the Earth’s albedo (reflectivity).

    Reflective sea ice is replaced by dark ocean in a warming world (http://c1.redgreenandblue.org/)

  • Permafrost: Permafrost is frozen soil composed of preserved organic matter and contains a significant amount of carbon.  In fact, it is estimated that the world’s permafrost holds 1.5 trillion tons of carbon. Because of this, it has long been considered a carbon sink (reservoir of carbon).  However, the warming from the last decade has begun to melt the permafrost and release its stored carbon into the atmosphere.  The primary problem with this is that a lot of the carbon is being released as methane, a greenhouse gas 25x as potent as CO2 over a 100 year time period.  The introduction of this carbon into the atmosphere will lead to even more warming and more melting of the permafrost…another vicious cycle.

    Simple Diagram of the Feedback from Permafrost Melt (http://sitemaker.umich.edu/section2_group1/arctic_issues__permafrost )

  • Water Vapor: With water vapor, a similar pattern occurs.  Warmer temperatures lead to increased levels of evaporation.  Since water vapor is a greenhouse gas, more water vapor means more warming and the cycle continues.

Water Vapor, another greenhouse gas. (http://www.treehugger.com/water-vapor.jpg)

Sources:

  1. http://climateprogress.org/2011/02/17/nsidc-thawing-permafrost-will-turn-from-carbon-sink-to-source-in-mid-2020s-releasing-100-billion-tons-of-carbon-by-2100/
  2. Hell and High Water by Joseph J. Romm
Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s