2010-11-25 11:44:42Draft article: Bicycle Feedbacks UPDATED
Rob Honeycutt



This is a first draft.  Looking for feedback on this article.  It needs some links and a little more data I think...

I'm also working on some illustrations to go along with this.  You science guys are going to have to tell me if this whole analogy works. 



Bicycle Feedbacks

Let's take a quick ride into climate sensitivity.

From the standpoint of the general public many of the issues in climate change can be confoundingly complex and difficult to grasp.  Many aspects of climate language can be counter-intuitive.  Even simple concepts like positive and negative feedbacks can be frustratingly difficult to get straight for the average concerned citizen.  A positive feedback is bad?  And what is the difference between a forcing and a feedback.  Even the word "forcing" used as a noun instead of a verb can trip up those who are not anointed into the sciences.

What can help clarify a broader understanding of these complex issues are good old fashioned analogies with a dash of metaphor thrown in to spice it up and capture people's attention.  And I think I stumbled onto a fairly decent analogy the other day while trying to better explain feedbacks and climate sensitivity.

Most of us know how to ride a bike.  Most of us know how to ride a standard modern bicycle with gears.  Fixies are all the rage right now but we're going to stick with bicycle technology from your basic run-of-the-mill mountain bike.

This analogy came up while trying to explain how the new cloud feedback study out of Hawaii (UHM) might affect the IPCC estimations of climate sensitivity.  So let's look at it this way...

The crank set of your bike represents the forcing mechanism on climate.  This can be any forcing.  Milankovitch cycles are a forcing.  Variations in solar activity are a forcing.  Volcanic activity is.  Manmade CO2, as it has exceeded the planets natural capacity to absorb the extra CO2, has also most recently become a forcing.  Anything that applies force, or relieves force, on the crank set is a forcing.

We often talk about the doubling of CO2 as having, alone and unto itself, the capacity to warm the planet 1.2C.  We could see this as a 1 to 1 gear ratio on a bicycle.  If you have a mountain bike that's equivalent to your smallest granny gear.  That's the force of pedaling (CO2 forcing) transmitted directly to the rear wheel and pushing the bike forward.  One crank rotation equals one rotation of the rear wheel.

Not a lot of force there.  It definitely causes warming but 1.2C of climate forcing is not going to cause us great concern.  But climate is more complicated than that.  Climate has a larger gear ratio than that.  

A forcing of 1.2C for doubling CO2 has feedbacks, and the feedbacks are varied and highly complex.  This is where the biggest challenges in climate science lay.  Feedbacks are the responses the climate system has to warming forces.  There are positive feedbacks like ice albedo, methane releases, [list more].  And there are also known negative feedbacks in the system like [create list].  These all act together to establish a gear ratio on our bicycle.

We have little capacity to alter these feedbacks in the climate.  We can't change the gear ratio.  The challenge scientists face is quantifying what the net feedbacks are.  They try to figure out what gear the climate system is in.

Before we looked at CO2 forcing by itself and said with a 1 to 1 gear ratio it would produce 1.2C of warming.  Feedbacks are mechanisms in the environment that act to change that gear ratio.  The IPCC states that they estimate climate sensitivity to be between 2.5C to 4.5C with 3C being best fit.  Using the 3C figure that would suggest that adding 1.2C of forcing gets just over double the response.

That means for a given force applied we propel ourselves down the road faster.  

Skeptics like Dr. Richard Lindzen have continually claimed that cloud feedbacks actually act to reduce the forcing from CO2 to less than 1.2C (Lindzen maintains clouds effects are a negative feedback).  In essence, he says, cloud feedbacks gear the forcing down.  He claims that cloud feedbacks act to drop us into a sub-granny gear less than a 1 to 1 ratio.  Most other climate scientists believe this not to be an accurate representation of the climate system mainly because the 1C of forcing we get from Milankovitch cycles could not result in the 5C-8C swings we see in glacial-interglacial cycles.  

The latest study from UHM is suggesting to climate scientists that cloud effects are a positive feedback.  This is very significant with regards to how fast we are warming, or in other words, how fast we expect our bike to move down the road to warmer temps.  The IPCC puts the uncertainty range between 2.5 to 4.5C.  If this new paper stands that means we are actually in a much higher gear than previously thought.

I might add to this analogy that the bike we are riding has no brakes.  There is only one option we have to control our speed.  Stop pedaling.  We at very least need to figure out quickly how to start putting less force on the pedals, and with regards to modern society that is an extremely complex political task.

Science is doing the best it can to tell us approximately what gear we are in and what the potential consequences are of continuing to pedal the way we are.  They are trying to tell us what they belief lay in the road before us.  It our job as individuals to evaluate their messages and make personal choices about how to respond.



2010-11-27 09:06:23

I found your switching from the physical world to the analogy and back a bit difficult to follow. Maybe you should do it just once.
2010-11-27 12:18:37
Rob Honeycutt

Thanks, Riccardo, I'll work on that.