Environmental Science Classroom: Climate Feedback Loop 5

The distribution of grasslands, forests, and deserts across the Earth's surface is the result of many variables, among which climate is a major determinate--especially mean annual temperature and mean annual precipitation.

Climate warming affects the world's vegetation.

As the Earth's average annual temperature trends upward under the influence of modern industrial human activity, vegetational communities like forests and grasslands find themselves, as climatologist Stephen Schneider explains, ' stranded in the wrong climate.'

Rapid climate change (i.e. over decades and centuries) provides stresses that overwhelm plants adapted to the previous 'normal' conditions. Many die. Dying forests present a double impact, as explained in the illustration below.  One is that dead trees either burn (increased forest fires in a new drier climate) or if they don't burn, they decompose. In either case, the fast burn of fire or the slow burn of decomposition both release all of the carbon that had been stored in the trees themselves. The second impact is that regions that previously supported forests no longer have trees that serve as a carbon sink.

Logical action to minimize this climate feedback loop would involve eliminating carbon emissions (the source of carbon dioxide in the atmosphere) and planting trees where trees can grow (the sink for carbon dioxide in the atmosphere).  Eliminate the source; re-establish the sink.

Climate Feedback Loop 5. © Fred Montague

Climate Feedback Loop 5. © Fred Montague

Environmental Science Classroom: Climate Feedback Loop 1

I have recently posted two "climate feedback loop" fact sheets. One described the ice/albedo feedback and the other discussed the methane loop. These are examples of positive feedback (or runaway feedback), effects that tend to amplify climate change.

The feedback effects shown below deal with humans causing an increase in the amount of water vapor in the atmosphere.  Here are two positive feedback loops (increased water vapor and increased cirrus clouds) and one negative feedback loop that tends to counteract global warming (the formation of low, thick, stratus clouds that reflect sunlight). There is uncertainty about which types of clouds will form, but it is likely that both are possibilities, depending on meteorological conditions.

Climate Feedback I: Water Vapor. © Fred Montague

Climate Feedback I: Water Vapor. © Fred Montague

Environmental Science Classroom: Climate Feedback Loops 3 & 4

Here is another unintended effect of our greenhouse gas emissions.  (See the January 4, 2013 post for feedback loop 2.)

Both of the global warming feedback loops shown below involve the potential release of hundreds of millions of tons of methane, currently frozen in tundra soils and shallow ocean sediments.

On a molecule-for-molecule basis, methane is 30 to 70 times more effective than carbon dioxide at trapping heat in the atmosphere.

In an exhibit of chemical irony, after about 12 years in the atmosphere, the methane molecules degrade (oxidize) into carbon dioxide and water vapor-- both important greenhouse gases.

Climate feedback loops 2, 3, & 4 are all positive feedbacks (or runaway feedbacks) and tend to amplify (rather than counteract) the effects of human greenhouse emissions.

Climate Feedback Loops 3 & 4 (methane). © 2013 Fred Montague

Climate Feedback Loops 3 & 4 (methane). © 2013 Fred Montague