Wizards of Oz

"Life is fraughtless ... when you're thoughtless."

20.5.08

Climate Change: Reprise

Back in September I wrote a post entitled "Climate Change: Yes, But Why?". My premise was that, while "climate change" is clearly occurring, the issue of causality needs more attention.

After that post, I asked some members of the Oak Ridge National Lab staff (including one of ORNL's corporate fellows, Dr. Tom Wilbanks, who was part of the Nobel-winning Intergovernmental Panel on Climate Change) to share their perspectives. Tom was able to point me in the right direction regarding infrared absorption of various molecules (e.g., H2O, CO2, etc.).

This month's WIRED (16.06) has a great point-counterpoint cover story (which, in the URL, is referenced as "heresies"). Among their proposed "heresies" are Embrace Nuclear Power, Carbon Trading Doesn't Work and China Is The Solution. I think these are great points -- points that hopefully will shift the dialog from impassioned proselytizing to rational decisionmaking. (However, a cursory glance at the WIRED comments section shows this to be a vain hope....)

The WIRED piece has motivated me to renew my own research into the causal relationships between solar radiation (which has been on a cyclical increase, with a corresponding decrease in sunspot number), natural phenomena, and human influence. I finally found a graphic that I find compelling:

This graphic (h/t Thomas Everth's GreenBlog in New Zealand) shows total atmospheric absorption of various frequencies of electromagnetic radiation, as well as individual absorption spectra for ozone (O3), water (H2O) and carbon dioxide (CO2).

It also overlays the distribution of incident solar radiation (most of which is between 200nm and 2μm wavelength, covering the visual spectrum of light as well as the near-infrared band) as well as the Earth's outgoing thermal radiation (covering the infrared-C band from 3 to 80 μm wavelength). Note that the x-axis (wavelength) is a logarithmic scale, going from 0.1 to 1, 10 then 100.

The red line shows the absorption of O2 + O3 (ozone). As expected, the left side of ozone's absorption spectra (wavelength below 200nm, in the ultraviolet spectrum) shows nearly 100% absorption. Our natural defense against harmful ultraviolet radiation is the ozone layer (which is depleted by chlorofluorocarbons, but that's for another post).

The blue line shows the absorption spectrum of water. While some have claimed that water vapor is the real culprit behind global warming (usually with some reference to how much warmer we are when there's a cloud layer), this plot shows that water's absorption spectra drops where the outgoing thermal radiation increases. Therefore, water is nearly transparent to the infrared-C radiation between 5 and 20 μm wavelength. This too is expected -- otherwise Forward Looking Infrared (FLIR) wouldn't work on humid nights or with a high water vapor content in the air.

What I find compelling is the green line showing CO2's absorptive properties. In particular, note the spike in absorption between 10 and 20 μm -- where CO2 absorbs nearly 100% of incident IR-C radiation.

When I first considered the absorption and scattering of radiation by molecules in our atmosphere, I initially discarded it as a cause for concern. My rationale was that the absorbed radiation would be randomly scattered, or re-radiated -- and therefore would balance itself out.

While this is true for incoming radiation from external sources (e.g., the sun), what I failed to consider is that we live exothermic lives on Earth. When we convert fuels into energy, we're also creating heat -- so the outbound radiation becomes the key consideration.

By adding the outbound radiation to the equation, with nearly half of the absorbed radiation being scattered back to the Earth, we can conclude that carbon dioxide is a major contributor to climate change.

What can we do about this? Invest in alternative, renewable energy sources (such as solar, which is getting more efficient in capturing the 1.3kW per square meter peak incidence from the sun; wind, with some models generating more than 6MW per turbine; and better batteries to store energy). Travel less (thanks, Internet). And save.

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7 Comments:

At 21/5/08 10:58 , Blogger Vinay Gupta - Hexayurt Project said...

I'm pretty sure that the panels from nanosolar and konarka are going to fix this presently. Electricity generation which is significantly cheaper than coal - and therefore much, much cheaper than nuclear - will stabilize and then cut CO2 emissions pretty rapidly.

I'm not sure why people aren't rallying around these companies and figuring out how to scale them as rapidly as possible. Nanosolar is supposed to ship 430 megawatts of panels this year... and we could really use two orders of magnitude more next year...

That, to me, looks like the solution. Kill coal first, then do gasoline as battery technology improves.

 
At 21/5/08 20:05 , Blogger Dan tdaxp said...

Truly an excellent post. Detail-oriented, problem-oriented, solution-oriented. Really, it's quite wonderful.

 
At 21/5/08 23:02 , Blogger deichmans said...

Vinay, I'm continuing to track your own blog (as well as http://hexayurt.com ) to keep up with the "unplugged" marketspace.

Dan, Many thanks! You've been blogging up a storm while overseas - some outstanding posts of your own these past couple of days!

 
At 22/5/08 01:14 , Anonymous ry said...

I've got a small quibble with your analysis that water is not that big in the 'C' range. That's not true at all, and your own data shows it. H2O bottoms out around 9-10microns but shoulders to both left and right of it in a non-insignificant amount. I'd have to get out my methodology text to do it right(being an O-chem guy instead of a quant or a p-chem) but you'd have to integrate under the curve to see how much it actually absorbs in said region to make that statement, with high accuracy. Like I said, it's a minor quibble. You can fine tune a laser or other detectors into very small ranges of wavenumbers(nanometers, microns, different disciplines use different names). So I don't think that FLIR works on a humid day is all that strong an argument. Again, quibble, not trying to genk the whole thing using the 'one brick in the wall is mishapped so the whole thing is faulty' fallacy.

Otherwise, put me in Dan's/Barnett's/"Skeptical Environmetalist" category.


Now, why is the water absorption important? We've got people saying we should move to a hydrogen economy. Well, water is about (approximate, and from memory) 80% as effective CO2(per mole (6.022x10^23 )of stuff))) at trapping heat. So, if we're generating more moles of water per kW are we actually saving anything? Those shoulders are not insiginificant. NOr is the fact that water absorbs in the other major region: incoming energy.

All those damn bond eneries and vibrational modes.(Gawd, I hated studying that stuff).

go nuclear, supported by geothermal, wind, and solar. At least until we get some kind of controllable and sustainable fusion reaction going(eh, in less than 500 years I bet).

Blame J over at Armchair for pointing me your way. Ask Dan, I'm waaaay annoying once I infest your joint. ;) --ry

 
At 22/5/08 07:49 , Blogger deichmans said...

ry, Welcome, and thanks for your great comments. I agree with your recommendation (go nuclear, plus solar / wind / geothermal until we get a working reactor, be it ITER or something else), and that the "shoulders" under the curve are significant.

Every solution has consequences: be it corn-based ethanol or the hydrogen economy you noted. Personally, I am not as concerned about water as a greenhouse gas -- largely due to the self-regulating nature of the water cycle. CO2 distribution is much more normalized, and its reclamation more demanding.

I will share one gripe I have about the graphic in the post. The curve for outbound IR emissions from the earth is labeled "255 K" -- or -18º C. Would the curve for 288 K (near the median of earth's ambient temperature) shift it to the left, and therefore *AWAY* from the CO2 absorption peak? If so, then water would be a far more troublesome molecule....

 
At 22/5/08 07:50 , Blogger deichmans said...

BTW, thx to J @ Armchair Generalist for the ry vector!

 
At 23/5/08 02:50 , Anonymous ry said...

Well, my complaint on water is mostly against the hydrogen economy. Sure, by LeChaltie's principle, all we'd get is an eq. shift. But where that shift ends up can matter(which you get to via a different mental pathway apparently with "Would the curve for 288 K (near the median of earth's ambient temperature) shift it to the left"). Producing tons more atmospheric water with a hydrogen economy doesn't sound all that smart to me because of the eq shift. But I'm not an atmospheric guy, so I could be full of it.

Yeah, we blame J for everything. ;)

 

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