Why can't we physically reduce CO2 in the atmosphere?

[PeaceForever]

When I was in high school chemistry class, we learned a procedure in lab to convert carbon dioxide into oxygen and solid carbon.

Why can't this procedure be done on a grand scale? If we can reduce the carbon dioxide levels in the atmosphere, it will ease global warming.

[phantom power]

1. Sure, but how much energy will it take?

where will you get the energy to do it?

[Goldmund]

2. ...and will the...

synthesis of the energy you use to do it produce twice as much CO2?

[PeaceForever]

3. Good question

Hopefully it would still result in more carbon being taken out of the atmosphere than put in.

I should investigate that.

[havocmom]

4. Can't do it cuz we have to keep knocking down trees to make way for roads

so we can drive more cars.....

Hey, anybody see a pattern here?

[wtmusic]

5. For the same reason we can't synthesize ozone

on that scale--it would create more of a problem than it would solve.

The problem we need to solve is dependence on fossil fuels.

[punpirate]

6. Energy balance?

How much energy, and how much CO2 produced in making that energy, to extract CO2 from the atmosphere and reduce that CO2 to carbon and oxygen?

By far, the most energy-efficient means is to reduce CO2 upload to the atmosphere and increase the amount of high-efficiency, low-water use vegetation to fix carbon by photosynthesis.

Cheers.

[jay-3d]

7. iron

I've read that we could try dumping iron into the south seas. The plankton is iron deficient in this area, and iron is the only limiting factor to a bloom. A massive phytoplankton bloom would absorb hug amounts of co2.

[mike_c]

10. IIRC pilot studies did not produce the expected results....

Here's one excerpt:

"The addition of the iron caused an initial doubling of the amount of phytoplankton, and the rate of growth quadrupled. However, after only one day, the phytoplankton activity leveled off. This was also relatively ineffective in reducing the amount of carbon dioxide in the air above the waters where the iron sulfate was added. The result was that only ten percent of the carbon dioxide was removed as compared to the expected amount for how much iron sulfate was added. The first reason why this experiment did not produce the expected results was there was also an increase in the amount of zooplankton, which consume the phytoplankton. Coale said, "The conclusion, then is that these waters must be deficient in one or more necessary trace nutrients, and adding the most limiting nutrient to those waters should promote rapid growth of phytoplankton. In theory, at least, rapid growth of phytoplankton should translate into increased removal of carbon dioxide from the atmosphere." Another reason may be that the iron particles combined with organic material, became heavier, and sunk to the bottom removing them from the surface area. The area of carbon dioxide and phytoplankton interaction is only within the first fifty meters below the surface. Researchers at MIT and Dartmouth College believe that zinc may be another limiting nutrient in the growth of phytoplankton. Their research shows that low concentrations of zinc slows productivity of phytoplankton.

Besides the fact that iron may not be the only limiting nutrient, there are other factors stopping scientists from believing that the fertilization of phytoplankton is a viable solution to the problem of global warming. In the words of Sallie Chisholm, a biological oceanographer at MIT, "It's prepostorous to think of messing with the oceans to solve the global warming problem." She believes that this is only a temporary solution and that deep ocean circulation would eventually bring this carbon dioxide back to the surface. Even the researchers of the IronEx project are not necessarily supportive of tinkering with the oceans on such a large scale. They only wish to show the validity of John Martin's hypothesis."

one edit: link-- http://www.cem.msu.edu/~cem181h/projects/96/iron/cem.html

First of 14,500 hits for a goog search on "iron plankton carbon."

[punpirate]

11. Here's an article supporting that:

http://www.eurekalert.org/pub_releases/1996-10/BNL-IWHI-091096.php

Here's a relatively recent study which says it won't help much:

http://www.scienceagogo.com/news/20040318210325data_trunc_sys.shtml

Neither brief seems to go into detail much about changes in the ecosystem, or the effects that a changed albedo might have on water and wind currents.

Cheers.

[yellowcanine]

8. Lots of problems with this kind of thinking

1) You would need to spew reagents into the atmosphere on a huge scale - cost is prohibitive
2) Unintended consequences - the reagents themselves may cause problems for plants, animals, humans, ecosystems, etc.


An "easier" way would be to try and stimulate plant growth to take up more CO2. For example, one proposal is to dump iron in the ocean to stimulate algal growth which would then take up CO2. However, this "solution" has the same inherent flaws of your proposal.

We can contribute to a solution by studying ways of sequestering carbon, for example, in the soil. It is possible to raise carbon levels in the soil by using tillage techniques that minimize soil disturbance, for example. If we could do this on a large scale significant amounts of carbon could be sequestered in the soil. Through "carbon trading" it might be possible to have power companies pay farmers to store carbon in their soil and thus make up for some of the CO2 produced by making electricity.

[mike_c]

9. there have been several proposals for physically removing...

...atmospheric CO₂. Virtually all depend on one of two things. The first is energy for inorganic chemical fixation and sequestration-- lots of energy, and of course the primary source of that energy is presently more hydrocarbon fossil fuels. The second is a series of proposals that rely on stimulating natural carbon fixation, but our understanding of the MECHANISMS by which we could stimulate the biotic portions of the global carbon sufficiently to make a real difference just isn't there yet. The Earth was a very different place when the great forests that produced all that coal and petroleum grew-- it's not presently possible to simply reverse the carbon release process and let photosynthesis clean things up. Additionally, there's a significant black hole in present models of the Earth's carbon budget, suggesting that the models themselves are either incomplete or in error (there's no question about increasing CO₂ in the atmospheric carbon pool, however).

[phantom power]

12. by the way: this is an issue for many alternate energy plans

Any hydrogen economy will have to grapple with this same issue. What energy source will be used to drive the cycle? Any fuel-based storage scheme, essentially. Biodiesel, H2, manufactured methane, whatever.

[factroid]

14. hydrogen

So, what could produce a problem using solar or hydro power to produce hydrogen for fuel cells, which have only H20 as a by-product? (use solar for manufacturing also) - I understand there is a new leap in photo-voltaic efficiency about to emerge also.

[phantom power]

15. it might work, but details matter

If you propose this plan: "We power engines with hydrogen, and produce our hydrogen with solar power".

then the following questions immediately apply: How much hydrogen do we need to produce per day, to supply our current energy requirements? How many hydrogen-producing plants do we need to make all that H2? How many terawatts of solar-power will you need to power those plants? How much will all those solar panels cost? Will those solar panels require more energy to manufacture than they will produce over their lifetime? (If the answer to that last question is yes, then the entire plan fails).

I don't have the answers to any of those questions, but if we're serious about actually *doing* any of these plans, the answers will need to be worked out by somebody. I'm not that guy.

[factroid]

13. the simple solution

The simple solution is to work with the natural balances, of course. All artificial methods to fix something we already put out of balance, by adding some 20 billion tons of CO2 per day to the 200 billion daily tons, will no doubt fail. We just need to increase engine efficiencies, migrate to fuel cell technology and other alternative forms of energy, and stop burning so much hydro-carbon fuel! Gaia knows how to keep the balance, but it's like force-feeding your dog on too much rich pork or salted ham. At some point it'll die! Of course, Gaia won't die, she'll just allow the diseased organisms (mankind) to be exterminated. It's our choice. Understand nature and have more wisdom, or perish. Very simple. I can't imagine how we could EVER fix 20 billions daily tons of CO2, and without some 'side effect' to deal with. It's just like allopathic medicine being used for every ailment. The key is balance. Keep it, or keep swinging back and forth out of balance until you die or find it. Also very simple. There is wisdom, and there is foolishness.

[NNadir]

16. This is dangerous territory because it appeals to perpetual motion

machine ideas.

That said, the hydrogenation of carbon dioxide is well understood, if not quite economic, at least right now. There are many reason why such hydrogenation would be superior to using hydrogen directly, most having to do with storage and transportation of energy from potentially remote locations.

One needs, of course, hydrogen. One can make hydrogen in only a few ways without exacerbating the greenhouse effect. Possible alternatives are solar (wind, PV and hydroelectric), geothermal (Iceland could become the new Saudi Arabia) and of course, in many ways the best option, nuclear energy.

It happens that wind, PV, hydroelectric have very low efficiencies for producing hydrogen, since they most likely depend on electrolysis, a process that is somewhat dubious on environmental grounds. Hydrogen however can be produced by thermal decomposition of water using schemes like the sulfur iodine cycle, which is often envisioned for high temperature nuclear reactors like HTGCR or molten salt reactors. It is possible to imagine a similar thermochemical decompositon scheme using geothermal energy, although it is certainly more problematic than the nuclear case. In places like Iceland, where electricity can probably be generated very, very cheaply, geochemical electrolysis/hydrogenation of carbon dioxide could be a viable scheme particularly because Iceland has few good carbon sources readily available. Of course the carbon dioxide would not be permanently removed from the atmosphere, but would instead be part a carbon cycle on a very grand scale.

Another problem with hydrogenating carbon dioxide is that it costs energy to collect the carbon dioxide from the air. However this is obviously not impossible, since it is exactly what plants do all the time.

[Bdog]

17. Bush cut the funding

http://www.aa.washington.edu/AERP/CRYOCAR/CryoCar.htm
Note: Due to lack of funding, this research project at the UW is no longer active. We have left this website up for general information purposes only. If you have questions regarding any aspect of LN2 vehicle technology, please direct your inquiries to the researchers at the University of North Texas.

Researchers at the University of Washington are developing a new zero-emission automobile propulsion concept that uses liquid nitrogen as the fuel. The principle of operation is like that of a steam engine, except there is no combustion involved. Instead, liquid nitrogen at –320° F (–196° C) is pressurized and then vaporized in a heat exchanger by the ambient temperature of the surrounding air. This heat exchanger is like the radiator of a car but instead of using air to cool water, it uses air to heat and boil liquid nitrogen. The resulting high-pressure nitrogen gas is fed to an engine that operates like a reciprocating steam engine, converting pressure to mechanical power. The only exhaust is nitrogen, which is the major constituent of our atmosphere.

The LN2000 is an operating proof-of-concept test vehicle, a converted 1984 Grumman-Olson Kubvan mail delivery van. The engine, a radial five-cylinder 15-hp air motor, drives the front wheels through a five-speed manual Volkswagen transmission. The liquid nitrogen is stored in a thermos-like stainless steel tank, or dewar, that holds 24 gallons and is so well insulated that the nitrogen will stay liquid for weeks. At present the tank is pressurized with gaseous nitrogen to develop system pressure but a cryogenic liquid pump will be used for this purpose in the future. A preheater, called an economizer, uses leftover heat in the engine's exhaust to preheat the liquid nitrogen before it enters the heat exchanger. Two fans at the rear of the van draw air through the heat exchanger to enhance the transfer of ambient heat to the liquid nitrogen. The design of this heat exchanger is such as to prevent frost formation on its outer surfaces.

As with all alternative energy storage media, the energy density (W-hr/kg) of liquid nitrogen is relatively low when compared to gasoline but better than that of readily available battery systems. Studies indicate that liquid nitrogen automobiles will have significant performance and environmental advantages over electric vehicles. A liquid nitrogen car with a 60-gallon tank will have a potential range of up to 200 miles, or more than twice that of a typical electric car. Furthermore, a liquid nitrogen car will be much lighter and refilling its tank will take only 10-15 minutes, rather than the several hours required by most electric car concepts. Motorists will fuel up at filling stations very similar to today's gasoline stations. When liquid nitrogen is manufactured in large quantities, the operating cost per mile of a liquid nitrogen car will not only be less than that of an electric car but will actually be competitive with that of a gasoline car.

The process to manufacture liquid nitrogen in large quantities can be environmentally very friendly, even if fossil fuels are used to generate the electric power required. The exhaust gases produced by burning fossil fuels in a power plant contain not only carbon dioxide and gaseous pollutants, but also all the nitrogen from the air used in the combustion. By feeding these exhaust gases to the nitrogen liquefaction plant, the carbon dioxide and other undesirable products of combustion can be condensed and separated in the process of chilling the nitrogen, and thus no pollutants need be released to the atmosphere by the power plant. The sequestered carbon dioxide and pollutants could be injected into depleted gas and oil wells, deep mine shafts, deep ocean subduction zones, and other repositories from which they will not diffuse back into the atmosphere, or they could be chemically processed into useful or inert substances. Consequently, the implementation of a large fleet of liquid nitrogen vehicles could have much greater environmental benefits than just reducing urban air pollution as desired by current zero-emission vehicle mandates.

* Funding for this project has been provided by the U.S. Department of Energy.

[CabalPowered]

18. 3rd Law of Thermodynamics

[DrWeird]

19. Third law of thermodynamics?

What does not being able to reach absolute zero have to do with reducing CO2.

[DrWeird]

20. Plant a tree.

Nothing reduces CO2 better than photosynthesis.

[NNadir]

21. Good point doc. n/t

[PeaceForever]

23. Yes, but I thought trees make only a tiny dent.

The following article, for example, explains it: http://www.straightdope.com/columns/030103.html

[AZCat]

26. Interesting article... different answers than mine (see below)

The two internet sites that Cecil Adams cites in his article are unavailable, but he lists their figures.

Assuming 4 tons CO2/person-year, one site gave 12 trees, the other 4 trees as the balance.

Compare to my 450 trees/person, assuming 5 tons C/person-year.

I wonder what the difference is (of course I could have made a mistake).

On Edit: I figured out what was wrong with the two links, I am checking them out now.

Review of American Forests assumptions(link):
From their site...
"American Forests' research in our Global ReLeaf sites shows that, on average, a tree removes .9175 tons of CO2 during the first 40 years after planting. However, as trees grow, they compete for rootspace, sunlight, and water. Therefore, three trees must be planted to ensure that at least one makes it to 40 years."

Calculations:
(0.9175 tons CO2)/(40 years)(2000 lbs/ton) = 46 lbs CO2/year

In my homework, we were using about the same number. Most of my calculations were with lbs C, not lbs CO2, so it may be a bit confusing. For the eucalyptus example: 22 lbs C/year ~ 44 lbs CO2/year, so the numbers are not that far off. Just remember that a ton of carbon is about two tons of CO2.

[AZCat]

22. I had a homework problem related to this a couple of years ago...

Here is the problem from my Power Systems Analysis class of a couple of years ago, taught by Dr. Henry Perkins.

Eucalyptus:

Eucalyptus is a fast-growing tree, adding as much as 12 feet a year for some species. One figure for yield is 400 ft^3/acre-year. Density (dry basis) is about 50 lb/ft^3. If we try to improve plant breeding, we might increase the yield, but this would be offset by the need to plant on marginal land. The heating value (LHV) is 8500 Btu/lb, which is at the high range for woods.

In growing Eucalyptus, we initially plant seeds in a nursery setting, transplant seedlings when 2-3 cm high to individual tubes, and then plant again in the outdoors. A planter can plant up to 1000 trees/day.

Assume a planting on a 3m x 3m grid. Data suggest that these trees can be harvested initially after 5-10 years. The yield figure of 400 above suggests a five-year cutting. After the initial cutting, the tree will regenerate (coppice) from the existing stump. Typically a tree will regenerate 5-6 times for a total lifetime of about 30 years.

Now let us see what Eucalyptus can do to meet the U.S. energy needs and to reduce C02 in the air.


(1) Figure how many trees would have to be planted to take up the carbon (in CO2) produced by a 400 MW coal-fired power plant burning coal of 60% carbon and 10^4 Btu/lb heating value. Assume a 30-year life-cycle for the trees and no burning of the harvest wood (we store it to make coal).

(2) If one person plants 1000 trees/day, how many people are required for planting (assume six cutting cycles before the replanting)?

(3) How much land (in acres) is required for the trees if we plant on a 3m x 3m grid?

(4) For these conditions, determine the CO2 "used up" in units of lb CO2/tree-year. This becomes a convenient figure to have.

(5) Using the above figure, determine the number of trees required to take up the five tons of carbon per person per year by planting Eucalyptus trees. For the U.S. population, how many trees are required? How many planters can we offer full-time employment to (these are former coal miners)?

(6) How much land is required for these trees when planted on a 3x3 grid? (Arizona is 113,000 mi^2 for a reference value).



I'll see if I can find my answers (my old notes are a bit scattered).

[PeaceForever]

24. I'll be interested in the answers

I suspect, unfortunately, that it would require an impossible number of trees. The earth, in other words, is fucked.

[AZCat]

25. Answers (fwiw)

Here are my answers, for what it's worth - some of my assumptions may be off.

400 MW ~ 12E12 Btu/yr.

From Power Plant: Assume Load Factor = 0.8, cycle_efficiency = 0.3

(12E12 Btu/yr)*(0.8)/(0.3)/(10E4 Btu/lb Coal)*(0.6 lb C/lb Coal) =
1.92E9 lbs C/yr = 960,000 tons C/yr from plant

Trees:

(400 ft^3/acre-year)*(50 lb C/ft^3)*(0.5 Carbon/Treemass) = 10,000 lb C/acre-year = 5 tons C/acre-year

(960,000 tons C/yr)/(5 tons C/acre-year) = 192,000 acres = 777E6 m^2

A grid with 3m x 3m spacing produces one tree every 9m^2

(777E6 m^2)/(9 m^2/tree) = 86.3E6 trees
Workers: Assume 5*50 = 250 work-days/year (weekends plus a holiday off)
We plant 1/30th of the trees every year (we stagger them)

(86.3E6 trees)/30 = 2.9E6 trees planted every year

(250 work-days/worker-year)*(1000 trees planted/day) =250,000 trees planted/worker-year

(2.9E6 trees planted/year)/(250,000 trees planted/worker-year) = 11.5 workers ~ 12 workers needed

CO2:

(10,000 lb C/acre-year)(44/12) = 36.7E3 lb CO2/acre-year

(1/9 tree/m^2)(4050 m^2/acre) = 450 trees/acre

(36.7E3 lb CO2/acre-year)/(450 trees/acre) = 81.6 lb CO2/tree-year

People: Assume US population ~280E6

(5 tons C/person-year)/(5 tons C/acre-year) = 1 acre/person needed

(280E6 people/USA)(1 acre/person) = 280E6 acres/USA

(280E6 acres/USA)*(450 trees/acre) = 126E9 trees/USA

(126E9 trees/USA)*(1/30 trees planted/total trees) = 4.2E9 trees planted/USA-year

(4.2E9 trees planted/USA-year))/(250,000 trees planted/worker-year) = 16,800 workers/USA

Land required:

(280E6 acres/USA)/(640 acres/mi^2) = 437,500 mi^2/USA

(437,500 mi^2/USA)/(113,000 mi^2/Arizona) = 3.87 Arizonas ~4 Arizonas

Answers:

1) A 400 MW coal-fired power plant requires 86.3 million trees to take up the carbon produced.

2) 12 workers are needed to plant this many trees (continuously)

3) 192,000 acres are required for these trees.

4) 81.6 lb CO2 is used up by one tree per year

5) One person (5 tons C/year) requires one acre, or 450 trees, to take up the carbon produced.
For a USA population of 280 million, 126 billion trees are required to take up the carbon produced.
This requires a workforce of 16,800 workers planting trees.

6) The land required for the trees servicing the entire USA would take up an area about four times the size of Arizona.

[NNadir]

27. These are reasonable values, and look acheivable on their face.

I would expect though, that there would be considerable health risk in such a scheme, particularly because wood burns with considerable soot production. Air pollution deaths would certainly rise in such a scenario. Indeed much of the air pollution related consequences in the third world derives from exactly this biomass source, wood. It is difficult to state what the effect on water demand would be. I suspect that water would be the most problematic option.

This is definitely not the low risk option. It would be better to grow trees to sequester carbon dioxide without burning them.

I think a biomimetic strategy rather than a pure biological strategy, i.e. the direct hydrogenation of carbon dioxide or carbon monoxide is to be preferred. The ultimate source of energy in this case would need to be solar, nuclear or (more rarely), geothermal all of which are relatively low risk strategies.

[AZCat]

28. Yeah- Perkins thought of that

It's tucked in the original problem set, where the questions are listed. It's the last sentence for question #1.

Interestingly enough, a lot of carbon is stored as limestone (CaCO3). I wonder if that opens up any possibilities.

[NNadir]

29. The problem with limestone is that one needs to make hydroxides as a

precursor.

For instance, if one wants to make Calcium carbonate, one reacts calcium hydroxide (slaked lime) with CO2. However, if one makes Calcium Hydroxide from Calcium Chloride, one needs to produce a chlorine molecule. The fate of the chlorine molecule will almost certainly be (long term) two molecules of hydrochloric acid, which will react with Calcium carbonate to give Calcium Chloride and carbon dioxide. So at best, the process is cyclical. It also consumes considerable energy to accomplish.

One can, of course, make Calcium hydroxide (or oxide) from limestone, but this process releases carbon dioxide.

I'm rather hard pressed to consider too many Calcium processes that don't produce acid. I suppose there are some silicate minerals for which this is possible, but I'm sure that such processes would be very expensive energetically.

[Bdog]

31. Joseph C. McNeil Generating Station Wood fuel facts

http://www.burlingtonelectric.com/SpecialTopics/Woodfacts.htm
McNeil wood fuel harvesting standards:
Protect aesthetic quality near hiking trails

Follow accepted soil erosion control practices

Promote healthy growth in forests

Protect wildlife habitat, endangered species, wetlands and streams


McNeil Station benefits:
Uses locally available fuel source

Consumes 180,000 tons of wood per year, which displaces 360,000 barrels of imported oil

Contributes to the regional economy ($90,000,000 since 1984)

Provides jobs for Vermonters

Improves Vermont forests


McNeil wood chip supply:
70% produced from low-quality trees

25% produced from residues (chips and bark from local sawmills)

5% comes from clean recycled wood


McNeil statistics at full load:
Produces 50 megawatts (MW) of power

Consumes 76 tons of wood per hour


McNeil air quality:
Air quality control devices limit stack emissions to one-tenth of the level allowed by Vermont regulators

Stack emissions are one one-hundredth of level allowed by Federal regulators


Did you know??
McNeil harvesting standards have improved the health and productivity of over 30,000 acres of Vermont forests.

These standards are unique to Vermont and are the most stringent of any wood consumer in the state.

Professional foresters monitor all harvests and a Vermont Department of Fish and Wildlife biologist must approve proposed harvests

Harvests must meet approved guidelines for forest management and soil and water protection

The McNeil Station provides a market for about 54,000 tons per year of wood residues otherwise slated for local landfills.


Wood is a renewable fuel which does not contribute to global warming.


The current annual harvest for all wood products is less than half the annual growth.

The McNeil Generating Station is jointly-owned by: BED (operator and 50% owner); Central Vermont Public Service (20%); Vermont Public Power Supply Authority (19%); and, Green Mountain Power (11%).

[NNadir]

32. Well, it's safer than coal, but not safer than nuclear. Wood burning link

Carbon monoxide, formaldehyde, acetaldehyde, benzene, toluene, benzopyrene, benzo(a)anthracene... this is just a partial list of the compounds found both in tobacco and wood smoke (Click on Woodsmoke 101 in the link below.)

Maybe the McNeil Generating Station only releases 10% of what's allowed, but isn't it entirely possible that 10% of what's allowed is still dangerous? No? Oh, yeah, I forgot. It's biomass, and it's automatically safe because it has the syllable "bio" in it.

Anyway, here's the website of the people who would like to ban wood burning because it's too dangerous:

http://www.webcom.com/~bi/welcome.html

There is no such thing as risk free energy. There is such a thing as risk minimized energy, the latter being another term for nuclear energy.

[AZCat]

33. Nuke energy = risk minimized energy?

I think this is a mischaracterization. In my view, risk minimized energy would be passive solar collection. Humans have designed dwellings that don't require additional energy input, although locations are limited if you exclude biomass (fireplaces).

Of course, even that has it's hazards, such as skin cancer from overexposure.

My point is this: I consider that using any source of energy outside of the above is not necessary for survival. We elect to use these sources of energy to support a lifestyle, and the costs/benefits vary for each. Sure, nuclear power has it's problems. So do all of the hydrocarbon fuels. Hydroelectric power? Yep - it depends on rainfall and can wreak havok with fish populations.
What I cannot condone is the Vice President of the United States claiming that, "Conservation may be a personal virtue, but it is not a sufficient basis for a sound, comprehensive energy policy." Conservation is part of creating an energy system that is efficient and sustainable. While we may choose to use more energy than strictly necessary because we decide that certain applications are beneficial, that doesn't mean that we shouldn't pay attention to how we use it.

[NNadir]

34. Wrong. Solar energy, except for wind, is not safer than nuclear.

This is a very common misconception, but it is about as wrong as another common misconception, that the "War for Halliburton" is a part of the "War on Terror."

The EU study on the external cost of energy which I linked here showed very clearly that solar PV energy is more hazardous than nuclear energy because the manufacture of PV cells is more dangerous (because of heavy metals, carbon dioxide generated in manufacture, and toxic chemicals used) than it is to build and run nuclear plants. The only country with a significant PV capacity, enough to make the study's comparison valid on an industrial scale, was Germany. The thread can be found buried here a few pages back in the Environmental section. I occasionally kick that up just to amuse myself.

Solar PV energy is, however, much safer than many other forms of energy, especially coal and oil. However the direct (as opposed to external cost) cost of solar energy dwarfs the cost of coal and oil (and nuclear) and therefore is not used widely. PV can be made to have relatively low direct cost in the presence of a "carbon tax," which I think is a good idea. If there is an idea whose time has come, a carbon tax would be it.

Sometimes for rhetorical purposes, I sometimes make statements that seem to imply that I oppose solar energy. This is not the case at all, since I believe we need to extend our ultimately exhaustible nuclear resources for as many generations as possible. I think it is ethical for us, with respect for the rights of generations millenia hence, to accept the extra risk associated with solar energy expansion. Solar energy is ideally synergistic with nuclear because it provides easily for daytime peak loads. Nuclear energy is far better suited for base load production than it is for peak load needs.

Your point about conservation is well taken however. The safest treatment of energy is simply to use it as wisely as is possible, rationally to minimize its use.

[AZCat]

36. I apologize - I was unclear

You are correct about solar energy cells. One of my professors wrote his Phd. dissertation on the life-cycle cost of photovoltaics, and there is some nasty stuff created as a by-product during the manufacture. They're not particularly efficient either, although efficiencies of ~40% have been reached in the laboratory lately.

When I speak about solar energy, I mean simply that - energy derived from the sun: heating your house by properly designing exposure to the sun; heating water by exposing it to the sun; retaining the daytime energy with the proper building materials. I live in southern Arizona, and very few people build their houses with proper induced air flows in mind, which can be an effective system for cooling a house during the day.

While solar energy is both diffuse and fluctuating, human habitation designers managed to work with it for millenia before the invention of air conditioning, and I think it is given short shrift in habitation design.

[NNadir]

37. You're right about that type of solar energy. It's very safe, and very

wise to use.

[Bdog]

35. Its not 10% its 1% of federally mandated emission levels

And their are many coal plants that can reduce their levels of emissions by using bio-mass.

[NNadir]

38. To zero?

As low as a nuclear plant?

What do you think they do with those benzopyrenes and particulates after they've removed them from the smoke stack? Any idea? Do they just wish that they no longer existed?

How frequently to they validate their output and who is responsible for auditing these procedures? When such systems fail, do they shut them down, or go on happily operating them until someone notices? What if they get wet wood that burns cooler and with more smoke? Do they shut down then?

I'm sure that the wood burning plants would be cleaner than a coal plant, which is like saying its nicer to have vandals as your neighbor than it is to have murderers. Still I'd be pretty NIMBY on either business. I'd rather have a power plant that was like a guy who everyone says is scary, even though he never hurts anyone, even though all he does is work hard, respect the law, delivers what he says he will deliver and keeps my neighborhood clean and safe, a nuclear neighbor. It would help pay my school taxes, give me clean energy and keep some of the more questionable nutcases in the world from getting too close to my home.

[Pol]

30. Better Ways to Do It

The energy cost for converting carbon dioxide to carbon and oxygen is very high. Given the megatonnage of carbon dioxide, we would need tremendous amounts of energy to remove even a fraction of atmospheric CO2. Where would we get it? Hydro power kills fish, wind power has its own problems and is more expensive, nuclear energy might work, but you could never build the nukes, and burning fossil fuels would only exacerbate the problem.

Sequestering the carbon dioxide in carbonates, the way Mother Nature does with some of it, is more cost effective, but still creates problems.

Proposals for massive floating kelp farms to suck CO2 out of the air/water have failed the economics test, raise significant environmental problems, and leave you with a stinking mass of kelp.

The frontrunner in sequestration technology may involve capturing the carbon dioxide output of power plants and the like, liquifying it and injecting it underground. This still requires energy but, from what I have read, appears to be more economical.

A better approach may be to fund non-carbon-based energy technologies and conservation initiatives, increase CAFE, encourage production of hybrid vehicles, tax the gas guzzlers,