A Few Things Ill Considered

A layman's take on the science of Global Warming featuring a guide on How to Talk to a Climate Sceptic.

Thursday, June 28, 2007

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What is CO2's Relationship to Temperature?

I just had a reader ask me this via email:

Hi Coby,

I'd like to know what models assume with regard to the relationship between radiation transmission through CO2 and its concentration in the atmosphere. Is it a linear decrease with ppm, exponential?

A sceptic website makes a big issue of this, on the grounds that a 10% (say) increase in CO2 will not produce a 10% decrease in transmission.

Thanks


Since I took the time to write a detailed answer I thought I would post it here as well:

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Hi Ted

This is actually correct. The relationship between CO2 and temperature rise (all other factors and feedbacks aside) is a logarithmic one not linear. This is not an assumption of model code or a parameter that is set, it is the output of model runs and is based on the laws of the physics of radiative gases as represented in the models.

The standard metric used to discuss CO2 and its effect on the climate is called "climate sensitivity" to CO2. Currently models are all clustered around a 3oC sensitivity per doubling, with figures from 2 to 4 all within the 95% probability range. So adding 280ppm to pre-industrial levels we would expect a 3oC increase in temperature. To get an additional 3oC warming (if this is the correct sensitivity figure) we would need to add 560ppm more, 3 more degrees requires 1120 more ppm etc. This relationship changes at extremely high CO2 and also at extremely low CO2 but it does apply to all conceivable contemporary scenarios.

Climate sensitivity to CO2 includes H2O feedback and sea ice albedo feedback, both positive, but it does not include ice sheet response which is considered too slow to include. Nor does it seperately include carbon cycle feedbacks. That is to say the figure is for a doubling regardless of source so if for example humankind does add an additional 280 ppm CO2 to the atmosphere and 3oC is correct we still may incur greater warming if carbon comes out of melting permafrost and/or suboceanic methane clathrates, both likely occurences.

Hope that helps!
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Monday, June 25, 2007

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Another Week of GW News, June 24, 2007

Courtesy of H.E.Taylor, here is this week's GW news roundup
(skip to bottom)
Click here to read more

Low Key Plug

My first novel Water was published May, 2007. An Introduction to the novel is available, along with the Unpublished Foreword and the Launch Talk. An overview of my writing is available here.

<regards>
-het

PS. You can access the previous postings of this series here


"I offer a simple proposition about predictions by experts and others. Here is my Law of Predictions: The more confidence someone places on an unconditional prediction of what will happen in human affairs, the less confidence you should place in that prediction. If a prediction comes with an estimated range of error, then the narrower that range, the less you should believe it." -J.E.Cohen, page 134, _How Many People Can The Earth Support?_

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Monday, June 18, 2007

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Another Week of GW News, June 17, 2007

Courtesy of H.E.Taylor, here is this week's GW news roundup
(skip to bottom)
Click here to read more

Low Key Plug

My first novel Water was published May, 2007. An Introductionto the novel is available, along with the Unpublished Forewordand the Launch Talk. An overview of my writing is available here.

<regards>
-het

PS. You can access the previous postings of this series here


"I give a lot of talks on the subject [of GW], cause that is part of my job here to try to educate, and inevitably there will be somebody stand up and say, 'Well you know,this is a problem for the future. Why should we worry about this now?' Generally a grey hair like me. And it used to really bother me. Now I just ask them two questions. 'Do you have any children?' Most of the time they will say yes, and I ask, 'Do you have any grandchildren?' Yes, we do have grandchildren. Then I say, 'You are, we are creating for them the world that they will have to live in. And you know what? If they don't like it, there's not a goddamned thing they can do about it. We've done it. So if you don't care about your kids, or you really don't care about your grandkids, then I think you ought to ignore this problem.' Boy the room gets real quiet." -Dr. Tim Barnett, in the film _The Force of Destiny: The Science and Politics of Climate Change_

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