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Climate Change: A Snowball of Warmth July 9, 2010

Posted by Jamie Friedland in Climate Change.
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This is a follow-up to the previous post, which explained feedback loops and their significance within the climate system in much more detail.  Please refer to that post for background information.

“Anthropogenic warming could lead to some impacts that are abrupt or irreversible, depending upon the rate and magnitude of the climate change.” -The Intergovernmental Panel on Climate Change, Fourth Assessment.

That irreversibility is the result of positive feedback loops.

There are a number of self-magnifying positive feedback loops in the climate system.  Like a snowball rolling down a snowy hill, these phenomena grow stronger as they continue.  All of them are triggered by a warming planet and in turn warm the planet even more.

The presence of all these warming feedback loops means that once the planet warms past a certain threshold, we won’t be able to reverse the effects and global warming will be unstoppable.  That is not to say that it will continue forever, but we will not be able to stop the full extent of the warming that will then occur.

As I wrote yesterday about the snowball analogy, a person farther down the hill could theoretically stop the rolling snowball while it was the size of a baseball or a basketball or probably even the size of one of those big yoga balls.  But you wouldn’t be able to stop the snowball once it reached the size of a car or a house.  Once the snowball gets that big, it’s going to roll all the way to bottom of the hill no matter what you do.

There is some point in that progression where the snowball becomes too big to be stopped.  A similar threshold exists for climate change; once the planet warms enough and there is enough CO2 in the atmosphere, we are committed to the full extent of climate change.

Scientists aren’t exactly sure where the threshold lies.  Currently, the atmospheric concentration of CO2 is 392 parts per million (ppm). Some scientists say the threshold is at 450 ppm.  Other say 500 ppm.  A few even say 350 ppm, which we are already past.  Either way, there is a point-of-no-return and it is close.

In this post, I will lay out the specific positive feedback loops that could make climate change unstoppable.

Sea Ice

As you’ve probably heard, arctic sea ice levels are declining rapidly as the oceans warm.  This sea ice decline is itself a positive feedback loop.  “Albedo” is a measure of how much radiation an object reflects.  What radiation isn’t reflected is absorbed (causing that object to heat up).  An object’s albedo is represented in decimal values ranging from 0.0 (0% radiation reflected) to 1.0 (100% radiation reflected)

Ice has a very high albedo, around 0.9.  It is very reflective (hence snow blindness and sun burns on the ski slopes) so it absorbs very little heat.  When solar radiation strikes sea ice, most of it gets reflected back up into the sky.  In the past, sea ice has covered much of the arctic ocean, turning the region into a giant mirror as far as solar radiation is concerned.

With warming waters, however, more and more of the arctic has lost its sea ice, exposing the water beneath.  Water has a very low albedo, around 0.1.  Instead of reflecting that radiation, it absorbs 90% of it and, as a result, heats up.  As sea ice levels decrease, more of the arctic is absorbing heat instead of reflecting it.  This, obviously, warms the water further.

Warming water melts more ice, exposing more water, which absorbs more heat, which melts more ice…you get it.  This is a classic positive feedback loop.

Water Vapor

When you think of a greenhouse gas, you probably think of carbon dioxide.  Most people are surprised to discover that water vapor is itself a greenhouse gas.  In fact, it is the most abundant greenhouse gas in the atmosphere.

As the climate warms, the atmosphere becomes more humid.  Warmer air can hold more water vapor.  As a result, as the planet warms, the air will be able to hold more of this greenhouse gas, which will cause more warming, which will allow the air to hold more water vapor…etc.  Positive feedback loop.

Methane Hydrates

You may recall from BP’s containment dome debacle that the procedure was thwarted by “methane hydrates.”  Methane hydrates are a frozen slurry of – you guessed it – methane (and water). Methane is a much more powerful greenhouse gas than carbon dioxide.

If the oceans warm to a certain point, these hydrates could melt and release their methane, which would rise through the water and enter the atmosphere.  There, they would increase the greenhouse effect, warming the oceans further, melting more methane hydrates, releasing more methane etc.  …there’s a pattern emerging here.

Methane hydrate deposits are found around the world and could amplify global warming.

Permafrost

Permafrost is soil that has been frozen for at least two years.  It contains a lot of dead organic matter that would be decomposed very quickly in warmer climates.  That decomposition releases methane, and global warming is melting that permafrost and making the arctic one of those warmer climates.

Like methane hydrates, as permafrost melts, it releases significant quantities of methane.  This, as you now know, soon enters the atmosphere and causes more warming, which melts more permafrost etc.

Western Siberia contains the world’s largest peat bog.  Its 385,000+ square miles (France and Germany combined) are estimated to contain 100 TRILLION lbs of methane.  It is already melting…

Others

Desertification, Amazon loss, cloud cover, and terrestrial phenomena such as forest fires and soil respiration may also form positive feedback loops for global warming, although they are less well established.

Conclusion

Climate propagandists dismiss this simple science and those who explain it as “alarmist.”  While it may be alarming, raising awareness about these threats is not dishonest or unduly sensationalist.  People need to know why the long-term threat of climate change poses short-term urgency.

Rest assured, though, even without these simple and highly probable positive feedback loops, climate scientists explain that global warming will still be “substantial and critical.”  We cannot afford to put off addressing climate change any longer.

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Comments»

1. The Bad Kind of Positive Feedback: Climate Change « The Political Climate - July 9, 2010

[…] trackback This post is about feedback loops and the impact they have on our climate system.  This followup post explains the specifics of the positive feedback loops described […]


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