Positive Feedbacks and Climate Change

(Why it might be appropriate to be a bit panicky)

Today's lecture on positive feedbacks and unstable equilibrium points was certainly
interesting from a theoretical standpoint, but when we actually start applying those
Ball-well diagrams to climate change models the consequences of positive feedbacks
become downright scary.

Positive feedback loops are those systems where a perturbation results in a chain of
reactions which propagate and exacerbate that initial push away from a stable state.
These perturbations are self-reinforcing, speeding up progressively and causing an effect
with nearly unstoppable momentum and potentially global consequences.

Many climatologists have identified several potential positive feedback loops in Earth
ecosystems that already are or are on the tipping point of starting to cause drastic
changes in the Earth's climate. I've collected a few here below not to induce (a potentially
necessary and productive) panic on the part of anyone who reads about them but just to
reinforce the huge potential of positive feedbacks to disastrously affect climate.

I've done my best to compile a large list of links for this information from both academic
and popular news sources. There are lots of scholarly articles but I know we don't have time
to read them all. Here are a few easy-readers /watchers, there's lots more information out there!
This is by no means completely representative of all of the work being done, nor all that we
know about potential feedback loops. I've tried to include some very important ones and some
that don't get talked about as much. There are many more…

Forests and Bark Beetles

Spruce bark beetles are spreading at an alarming rate in boreal forests. There are millions of dead acres in the US and Canada due to the infestation. Normally, the bark beetle has a two year life cycle. With rising temperatures in high latitudes, bark beetles are able to condense their life cycles to a single year. Causing enormous outbreaks. Furthermore, because of warming temperatures they've expanded their range north into new, previously untouched forests. Not only are they killing trees, they are leaving them highly susceptible to fire which has the potential to even further inflame the problem.

Rising arctic temperatures -> increased spruce bark beetle populations -> increased mortality of boreal tree species -> decreased carbon dioxide sequestration -> increased atmospheric carbon dioxide -> rising arctic temperatures…

Links:

An NPR audio report on Bark Beetles and increased fire threat in Colorado.
Timber Supply and the Mountain Pine Beetle Infestation in British Columbia, a report from the Ministry of Forests, 2003.
A Planet Arc article. "The Canadian Pine Beetle Now 'Catastrophic'" 2002
A newspaper article from the Glenwood Springs Post Independent: "Beetles won't give a truce to the spruce" 2006

Albedo and Arctic Ice

Ice and snow have a very high albedo reflecting a high proportion of the sun's light back, away from the Earth's surface. Oceans and land have a much lower albedo, meaning they absorb more heat energy from the sun's rays. This will in turn result in higher temperatures and faster melting of the high albedo ice.

Increased temperatures -> faster melting of ice sheets -> lower levels of albedo -> higher heat absorption by Earth's surface ->
increased temperature

Links:

A NASA video on the ice albedo feedback loop:

More information from NASA on changes in ice and subsequent changes in albedo.
More discussion of the ice-albedo feedback loop.

Water vapor

Carbon dioxide might be the poster child for greenhouse gases but water vapor is actually the most abundant greenhouse gas in the atmosphere. As the atmosphere warms, its capacity to hold more water vapor increases - i.e. humidity will increase. As more water vapor enters the atmosphere more heat will be trapped and more water will evaporate, further increasing temperature.

Increased temperature -> increased evaporation and increased water retention capability of the atmosphere -> increased atmospheric water vapor -> increased temperature

Links:

A NOAA (National Oceanic and Atmospheric Administration) report on greenhouse gases.
A newspaper article in Science Daily, Feb 2009.
An interesting science blog entry on water vapor as a greenhouse gas.
Water vapor in the CSMonitor.
A special report from the American Geophysical Union from 1995 - we've known about this for a long time!

Photosynthesis in the Oceans

Photosynthesis doesn't just take place on land, in fact huge amounts of carbon dioxide are sequestered by the trillions of photosynthetic phytoplankton all over the world. NPP has dropped by about 6% though over the last two decades and scientists think the cause might be rising ocean temperatures. Without these photosynthetic organisms billions of tons of carbon will not be sequestered in the oceans and will instead be left in the atmosphere causing even more warming of the oceans.

Increased global temperatures -> increase ocean temperatures -> decreased numbers of phytoplankton -> decreased carbon sequestration -> increased atmospheric carbon dioxide -> increased temperatures

Links:
A video from a program at Northwestern University on global warming. Here is a lecture about the oceans:

A NASA report on photosynthesis levels in the ocean.

Permafrost and Carbon Sequestration

An enormous about of carbon has been frozen and effectively sequestered in the permafrost of the Earth's arctic regions. As temperatures warm though this permafrost is melting, enabling decomposition and a huge volume of carbon release into the atmosphere. This carbon from respiration will then increase temperatures in yet another positive feedback loop.

Increased global temperatures -> increased melting of arctic permafrost -> increased decomposition of carbon stores in high latitudes -> increased atmospheric carbon dioxide due to decomposer respiration -> increased global temperatures

Links:

Permafrost and climate change:

"Tomorrow's Climate Today - the End of Permafrost"

A short blurb from the US geological survey on the increasing availability for permafrost soils to microbes.
A NASA publication on climate change and permafrost.
An article from Environmental Research Letters, an online journal source.

Great post, whoever posted this! I dare say this is how the wiki was intended to be used!

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