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Friday, March 22, 2013

Removing atmospheric Carbon Dioxide

Some hair brained suggestions have been made for removing Carbon dioxide from the air or even from the smoke stack of coal fired power stations.  Suggestions have also been made about putting little mirrors in the Le grange point between us and the sun to cool off the earth.  Just imagine how much fun this would be  at the next economic crisis when funds are cut for  constantly  renewing these mirrors and we already are up at, say, 500ppm carbon dioxide. not to mention a likely reduction in photosynthesis from the shading which would cause a reduction in the uptake of carbon from the air.

I have read that in order to remove carbon dioxide from the stack of a coal fired power station we would need to use an extra 30% more power.  In other words you would have to burn 30% more coal.  I wonder if you would also have to burn 30% of the 30% which equals 9% more coal to sequester the  30% extra coal you burnt.  Then you would have to burn 30% of the 9% which equals another 2.7% to take up this extra 9% worth of carbon dioxide.  Lets go one more.  30% of the 2.7% is 0.81%.  So far we are up to a total of 42.51 percent more coal burnt in order to sequester the carbon dioxide produced.  Sorry I'm being facetious.  It could be that the boffins calculated the sequence and it came to 30% overall.  Perhaps they will put in wind turbines to generate the power to remove the carbon from the smoke stacks!!!!

It is axiomatic that we have to first stop putting more sequestered carbon into the atmosphere.  Just imagine the stupidity of trying to pull Carbon dioxide out of the atmosphere while coal fired power stations are pouring more into the air.  Not rocket science - right??

However this blog is about measures we can take to remove Carbon dioxide from the air.

Let's get real about this.  Has anyone noticed that the level of Carbon dioxide goes up and down by 7ppm during the year or more accurately, 8 up and 6 down.  Natural processes are far stronger than anything we are likely to come up with.  How about if we could get the system to go up 6 and down 8.  Let's see what natural processes we could encourage.

And while we are at it, the world production of Carbon dioxide from fossil fuel in 2008, the latest figures I can find, was 2.988 x 1013 kg.  The mass of the earth's atmosphere is about 5 x 1018kg.  Dividing one by the other and we see that we are putting enough Carbon dioxide into the atmosphere to raise the level of Carbon dioxide by 5.97ppm each year.  In actual fact the net rise in Carbon dioxide is around 2.5ppm per year (and rising).  If we stopped the use of all fossil fuel, this net uptake of about 3ppm would not stop.  At least at first, we could expect Carbon dioxide to decrease at about 3ppm per year.  However, we could even do better than this.

There are a lot of carbon sinks we could encourage. 

Amount of CO2 in the atmosphere
The figure of 5 x 1018kg of atmosphere was from wikipedia.  Here is a calculation that comes up with a slightly different figure.
*The pressure on each square metre of land at sea level is 10.3 tons.  In other words, the column of air above each square meter weighs this amount.
*The area of a sphere is 4πr2 so the area of the earth with a radius of 6371km is 4π x 63712 = 5.10 x 108 square kilometers.
*There are 106 square meters in a square km so the area of the earth is 5.10 x 1014 square meters
  *5.10 x 1014 square meters times 10.3tons per square meter equals 5.25 x 1015 tons of atmosphere## (= 5.25 x 1018kg

*The Carbon dioxide concentration is just about to reach 400ppm so I will use this figure.  Note that this is the parts per million by volume.  To calculate the weight we must multiply by 44/29.  44 is the molecular weight of CO2 and 29 is approximately the molar weight of air.  The weight of Carbon dioxide in the atmosphere is therefore 5.25 x 1015 x 400 / 106  x44/29 = 3.186 x 1012tons of CO2 in the atmosphere.

Now that we have a handle on the size of the problem, let's look at how we could allow Gaia to remove the Carbon from the air.

Stop the Production of Palm Oil and clear fell logging and let Open fields revert to jungle
A mature jungle, by definition, does not produce any net oxygen or remove any carbon from the atmosphere.  The rate of trees falling and rotting is equal to the rate of photosynthesis.  (that is the meaning of mature - or at least one definition of the term).  In the tropics where the soil is above about 25degrees C, humus doesn't accumulate so mature tropical jungles, while they sequester (hold) a lot of Carbon,  do not remove any net Carbon  from the atmosphere.

A growing tropical jungle is a different beast all together.  You only have to look at what happens when a forest giant falls in a mature jungle.  The little saplings which have been stunted from a lack of light shoot up at an astounding rate. Pretty soon that part of the forest is inpenetratable.  The trees compete and eventually a few are left and they contain huge amounts of wood with its sequestered carbon.  As a tree continue to grow, it continue to sequester more carbon dioxide and this continues until it dies and returns its carbon to the atmosphere.

Let's say a certain type of wood is 50% water*.  That is to say it is half wood, half water.  So in 100kg of freshly cut wood you have 50kg of actual wood.   About 50% of dry wood is carbon.  Carbon has an atomic weight of 12.  Oxygen, 16.  So CO2 has a molecular weight of 44.  Every kg of carbon sequestered in wood represents 1kg x 44/12 equals 3 and 2/3 kg of carbon dioxide removed from the atmosphereTo grow  100kg of wet wood the tree has actually removed 183kg of carbon dioxide from the air.

* note that in the above link, they use the amount of water divided by the amount of dry wood.  I think this is a little confusing as they get 100% moisture or even more, depending on the species of tree.  I think the amount of water divided by the freshly cut wood is less confusing.

So if we stop producing palm oil and let the jungle take over again, a huge amount of Carbon will be sequestered from the air.

On any land where logging is practiced, build the logged wood into long term structures and replant.
If you look at the above link under the words "50% of dry wood is Carbon" you will see a calculation that for Douglas Fir on the coast of BC with a 70 year rotation Assuming you build the lumber into long lasting structures.  Such  a forest will result in the removal of 5 tons of CO2 per hectare per year.  This assumes that only the milled timber goes into long term structures and doesn't assume any use for the waste wood such as paper, press board or charcoal for soil improvement and sequestration so it is a very conservative estimation.  There are 100 hectares in a square kilometer so each square kilometre planted in Douglas fir on the coast of BC would remove 500 tons of CO2 per year.  The results are so variable for different areas and different species that I am not even going to try to estimate how much CO2 could be removed from the atmosphere by  logging and using the wood for long lasting structures.  However, using just this approximation you can see that it is substantial.

Turn wood waste into charcoal and use in tropical soils
Humus does not accumulate in tropical soils the way it does in the soil under temperate forests.  However, it has been found that charcoal can replace humus in tropical soils.  It is stable and serves the same purpose of storing nutrients and releasing them to plants.  This is called Terra Preta and it has been found in certain areas in the jungle where generations of people have incorporated charred organic material into the soil that they use for growing crops.  Tropical soils are very poor for agriculture partially due to their lack of ability to store nutrients.  Add charcoal to these soils and they are markedly improved.

Stop,,,,, Completely Stop the Harvest of Whales
Many species of whales feed at depth and poop on the surface.  This has been termed the Whale Pump and in pre-hunting times must have brought mega quantities of nutrients up into the photic zone. Whales also take nutrients from polar waters to oligotrophic* tropical waters where they go to give birth.  While many species of whale do not feed in the birthing areas, they feed their babies who poop nutrients into the nutrient poor tropical waters.  The phytoplankton gets  nitrates, phosphates and all sorts of other 'ates' from this rich source of manure and absorb carbonate from the water to build their bodies.

* Nutrient poor.

The Carbon gradient from the air to the water is therefore increased and the sea water can absorb more Carbon dioxide from the air.  It is estimated that about half of the Carbon dioxide we have produced has been absorbed by the oceans.  If this was not so, we would be approaching an atmospheric concentration of around 550 ppm now instead of 400ppm.  As with any reaction, as it proceeds it slows down.  At some point, the oceans will be saturated with respect to carbon dioxide and will cease to absorb any more.  At that point, other things being equal, our 2-3ppm yearly increase in Carbon dioxide will jump to 4 to 6ppm.

Long before that happens, though, the oceans as we know them will be dead.  Already there are indications that Pteropods, a swimming snail that serves the same function in the food chain as krill, are having trouble forming their shells because of ocean acidity.  Note here that if we restore the whale pump, not only will the oceans  be able to take more carbon dioxide out of the oceans  but the danger to the ocean food chains will also be reduced.  It will also increase the amount of fish we can take sustainably from the oceans.

Put Half of the Oceans off Limits for Fishing.
Our catches of fish are pitiful compared to what they once were*.  We have destroyed so many populations that it is amazing that the oceans still function.  The amounts of carbon stored in the fish, invertebrates plankton and so forth must have been huge.  We have fished out the oceans, eaten the fish, pooped out the residue and released all this Carbon dioxide into the air.  Let the fish stocks recover and they will once more hold mega quantities of carbon.

*Read the book Sea of Slaughter by Farley Mowat to get an idea of just what we have destroyed.

Even better, have you ever seen recreational fishermen, line fishing just on the borders of the tiny marine reserves  we have set aside. The catches there are great as adult fish from the reserves look for new sources of food outside the reserves.  Imagine what the fishing would be like if we set half of our areas aside as no fishing zones.  There would no longer be any need for FADs, drift nets, bottom trawls or purse seines.  The fishing would be so great that only hook and line methods would be necessary*.  We not only sequester carbon but improve our fisheries at the same time.

*Mowat's book again.

Protect our Corals
Sea level is going up at about 3mm per year.  No matter what we do, it won't slow down any time soon.  There will be an overshoot even if we stop all carbon emissions tomorrow.  Over the whole transition from a glacial, 20,000 years ago to our present Holocene interglacial sea level rose at about 6mm per year although there were intervals in which the rate rose to about 56mm per year.  Coral skeletons are CaCO3 and are a tad over 60% carbon dioxide as are the shells of mollusks (oyster reefs) and any other structure made from Calcium carbonate.  As the sea level rises, the constraint of the surface is removed and corals can grow upward.  If our corals are healthy, they will absorb large quantities of carbon dioxide as they grow upward.  If we stop acidifying and warming our oceans and take a few other measures to re-establish the health of our coral reefs such as not fishing certain species,  corals will help us get rid of atmospheric CO2.

Let Grasslands Recover
Many new civilization mine their dirt until there is nothing left and the civilization collapses. At the very least we have to adopt farming practices that stop this erosion.  Far better if we can restore the environment that existed, for instance, on the great plains of North America.  The plants of grasslands are mostly under ground.  This an adaptation to fire.  Grass fires are intense but if short duration and the roots and stems of the grass remains to sprout leaves at the next season.  However, we don't want fires and there is a far better option.    Have a look at this Ted Talk by Allan Savory,

Reflood Bogs
Bogs, or wetlands as they are often called sequester carbon at a great rate.  This is especially so if the bottom of the bog is anaerobic.  Cellulose is refractory under anaerobic conditions,  The Hula in Israel is a good example.  It is a wetland in the rift valley upstream of  the Kineret (sea of Galilee).  The Israelis drained it and turned it into farmland.  The peat which had accumulated over Milena started to oxidize and release nutrients and carbon .  It polluted the Kinerit from which Israel draws her water.  A few decades ago, Israel realized the problem and re flooded the Hula.  Now it once more sequesters carbon and cleans water flowing through it to the Kineret 

Put Nutrients back on to the land
The Chinese have managed to keep an agricultural civilization going on the same piece of land for over 5000 years.  She did this by recycling all animal and human wastes back on to the land.  The flush toilet is going to be China's undoing unless they have systems to cycle the nutrients from sewage plants back on to the land.  This sort of fertilizer has the added advantage of containing much organic carbon so it feeds the micro-organisms of the soil.  Think of the plains of Africa or North America in their pristine state.  Every bit of waste, every body went back into the soil.  The Indians of the great planes even put the bodies of their dead on platforms for the birds and insects to return to the Great Spirit.  We have depleted the carbon content of our soils.  Restoring the system would pull even more Carbon out of the atmosphere.

Allow Beavers to Repopulate Every Stream Possible
Beavers have a number of effects with respect to carbon sequestration.
1) by raising the water table around their dams, Beavers increase the growth of all the vegetation.
2) by capturing the spent salmon after they have spawned, Beavers hold a valuable source of nutrients which came up from the sea.  These nutrients are cycled away from the dam in the droppings of all the animals that get some of their food from the beaver pond and its immediate surroundings.  Plant growth including forests is stimulated, sequestering more carbon.
3) by burying cellulostic material,  Beaver dams settle out silt from the water and capture bed load.  All the bits of cellulose and even their lodges and dams are eventually buried and become a deep carbon rich deposit.  When agricultural man found this rich bottom land, he drained it and mined it with his crops much as was done in the Hula.  The more Beaver dams we can allow to flourish, the more carbon we will remove from the atmosphere

Protect Boreal forests
The tree line is moving northward with climate change.  This mimics what happened when the continental glaciers left the land.  Forests reestablished and much carbon was sequestered.  The forests are going to creep northward.  We must just let them do so without hindrance.

Final Note
Most of the systems above involve getting nutrients back into natural systems and then protecting them so that they can build up their biomasses and lock up carbon dioxide.  With a population that is already decreasing in many of the countries of the world and the means available to assist countries that haven't reached this favourable situation, we should soon be able to return land to nature*.  Most important, though, is that we cease to use fossil fuels.  Besides they are far to valuable to burn.

*See the TED talk by Monbiot  on re-wilding.

Sunday, March 10, 2013

The real strength of methane

Methane, (CH4) as everyone knows is a more powerful green house gas than CO2.  It is often quoted as being 20 times as powerful as carbon dioxide and often there is a further phrase in the sentence; namely "on a one hundred year basis".  What does this mean.

When methane is released into the atmosphere, it begins to react with oxygen (as OH) and turn into carbon dioxide.  The half life of methane has been variously estimated.  I will use the often quoted 7 years for illustration.  Put a kilogram of methane into the atmosphere today and in 7 years half of it will be left,  in 14 years a quarter.  In 21 years an eighth, in 28 years a sixteenth and so forth.  Over a hundred years, the warming that this kilogram of methane will contribute to the earth is a certain amount.  The exact amount is not important for this example since we just want to be able to compare methane and Carbon dioxide.

When Carbon dioxide is released into the atmosphere it is stable.  It is not broken down or combined with anything.  However, photosynthesis takes it up.  A figure I have heard quoted for the half life of a quantity of carbon dioxide released into the atmosphere is 100 years.  If you release a kg of Carbon dioxide into the atmosphere today, in 100 years, half of it will still be there.*

*If you have better figures for the half life of these two gases, plug them into the formula below and see what result you come up with.

If you are fluent in calculus you can do a better calculation than I will do below but the following calculation, while not exact, will be easier to follow.  It is a pretty good first approximation.

First off we need the formula for the amount of a gas left in the atmosphere.  It is:

At = A0 x 1/2t/h

At = the amount at time t
A0 = the amount at time 0 (when you released the gas)
t is the time in years that has elapsed since the release
h is the half life of the gas in the air in years
     note that t/h is the number of half lives that have passed.

Looking at methane first:
After the first 7 years, half a kg of methane is left from a kg released.  You start with 1, end with a half.  The average is (1 + 1/2)/2 = 3/4.  Do the second 7 year period.  It is (1/2 + 1/4)/2 = 3/8.  You see the way this is going.  The next few are 3/16, 3/32, 3/64 etc.  If I add up 14 of these which nearly makes up 100 years you come up with a number very close to 1.5.

Note I could have done one year intervals to find the total effect over 100 years when compared with the effect in the first year but as long as I use the same interval for Carbon dioxide, the relationship between the numbers remains almost the same. 
Online Graphing
Make a graph

The pink shaded area is a graphic representation of the amount of methane which causes global warming over a hundred year period following an initial release.

Now for Carbon dioxide
Using h as 100 years and t as seven years, for the first 7 year period, you start with 1kg and end with 0.9256kg.  Average 0.9763.  Continue for each 7 year period and add them up and you come to 9.621.

Online Graphing
Create a graph

The pink shading represents the amount of Carbon dioxide remaining after an initial release.  That large amount of Carbon dioxide has only 1/20th the green house gas effect as the small amount of Methane in the first graph

In numbers, despite a relative 6.414 (9.621/1.5) times as much Carbon dioxide in the atmosphere over the 100 year period as methane, from an initial release of a kg of each, methane still caused 20 times as much warming as the Carbon dioxide.

Since 6.414 X 20 = 128,  Methane,  is 128 times as potent a green house gas as carbon dioxide.  Note that I am simply reverse engineering what the scientist worked out for the relative effectiveness of these two gasses  They then calculated the true value based on the difference in their half lives.  I can't find the original work that says how effective a greenhouse gas each gas is.  Does anyone out there know where the original work is to be found.

So what does all this mean.  As long as methane is being released at a more or less constant rate, the X20 figure makes sense.  It reaches an equilibrium between  release into the atmosphere and oxidation and indeed the times 20 figure expresses the long term effect of the same amount of each gas released over a hundred year period.  Where this nice scenario breaks down is if the amount of methane being released is accelerating and it seems to be doing just that.

Massive methane seeps have been observed, especially over the vast Russian Arctic continental shelf where areas of bubbling of a km in diameter have been observed.  Methane is also coming out of the thawing permafrost.  Worse still, the amount of methane stored in these two locations plus deep sea methane is of the same order of magnitude with respect to the quantity of carbon contained, as all the carbon we have burnt so far plus all the reserves we know about.

I can't even imagine the implications of releasing just the Arctic methane over, say a decade,  with a potency kilogram for kilogram of more than 100 times that of carbon dioxide.  It would almost certainly cause enough warming to release a lot of the rest of the stored clathrates on, for instance, the ocean bottom.

It may be too late.  The only solution I can come up with is to sit on a chair, put your head between your knees and kiss your nether regions  good by.  I hope I am just being an alarmist and I have this all wrong.

Incidentally, as counter intuitive as it seems, if we could find a way to light most of the methane seeps and turn them into carbon dioxide, that would be a great help.

Three days later
I wish I could say I had got out my calculus books and worked out the integral but I didn't.  I found this most amazing site on the web.  You put in your formula and it does the integration for you.  I can't seem to get my blog to do mathematical notation.  If anyone knows how to do this, please let me know. The notation in the following paragraph is messy.
  Check it out.

The integral of A times (1/2)(t/h) is minus A times h times 2(-t/h) divided by log2.  Doing the calculation over 100 years for both Methane, using a half life of 7 years and Carbon dioxide, using a half life of 100 years, there is 7.14 as much CO2 in the air over that period, from the same initial release, as there is CH4.  In other words, with only 1/7.14 as much CH4 as carbon dioxide, the warming effect is 20 times as much.  The instantaneous heating effect is therefore 7.14 times 20 equals 143 and not 128 which I calculated using the interval method.

If you look at this site, the situation seems even more dire.  It reports that despite the concentration of methane being only 1/209 th of the concentration of carbon dioxide, it has a radiative forcing effect of 0.51W/m2 compared to 1.85W/m2 for Carbon dioxide.  This would indicate a relative heating effect of 758 times.  I hope someone has made a mistake somewhere.  These results are probably on a volume basis which would explain some of the discrepancy.

ie.  If we had a serious evolution of methane from the bottom of the Russian Arctic continental shelf or from the permafrost of the northern regions, the warming in that year would be spectacular.*  If no more methane was released, the effect would half each 7 years but the likelihood is that a big increase of methane would trigger off more and more deposits to release their methane.  Since the methane deposits are said to be greater than all the fossil fuel we have used so far and since, in the short term, methane is so much more powerful than Carbon dioxide, we may just possibly be in a spot of bother fairly soon.

Note that the West Antarctic ice sheet is said to be in the process of disintegrating and there are some indications that methane may be trapped under the Antarctic Ice sheets.

Incidentally, this may be an explanation for the end of glacials such as occurred 11,500 years ago and periodically during this present ice age which is 2.5 million years old so far.  If methane clathrate collected under the continental ice sheets, from buried swamps and seeps from fossil fuel deposits, it would sit there ready to be released if the ice started to melt.  Since methane is so powerful, an amount only a hundredth as much as would be needed than if it was Carbon dioxide to start a run away green house melting.  We wouldn't see the methane in ice bubbles since it is rapidly oxidized to carbon dioxide.  This may also be part of the explanation for the sudden rise in Carbon dioxide seen in ice bubbles during the end of the glacial.  Note that a top so called Firn layer of an ice sheet doesn't yet have closed bubbles and has some exchange of gas with the Atmosphere.

There is another little wrinkle to this story.  Clathrates are a sort of permafrost.  The clathrate ice holds sediments together on the Continental shelves and slopes.  As the clathrate disintegrates, not only does this "glue" disappear but the evolving bubbles expand and make the sediment into sort of a fluidized bed.  Have a wee tremor and this porridge can start to collapse and flow down hill.  There are indications that land slides on other continental shelves have caused localized but very severe tsunamis.  One would suspect that the first place we might see such tsunamis would be in the Arctic where methane evolution from the bottom is accelerating.

As Pat Condell would say, raising two fingers.  "Peace"