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Carbon Sequestration using Trees

We don't need to develop any new technology for removal of carbon from the atmosphere. We already have a very successful method of carbon removal. They are called trees (and other plant life.)

I suggest the planting of massive forests of ironbark trees. The timber of the Ironbark tree is heavier than water - density of 1120 kg/cubic metre dry (it would be less as new timber but still greater than the density of water -1000 kg/ cubic metre). When the trees have grown they could be harvested, taken to the coast and towed out to sea and sunk into deep ocean. In deep ocean there is little free oxygen or aerobic bacteria so breakdown of the wood would be slow, the carbon would be effectively locked up for centuries. This would need to be proven before large scale implementation however a quick search on the internet found a company that was claiming to have harvested timber from underwater sites that were 950 years old (1050AD!) and they were still in usable condition. I am sure these timbers would not have been from deep ocean where I would suggest sequestering would occur. While we should not use solutions that give future generations a problem to clean up, if we can get 500 years of sequestering from this method (we may well get a heck of a lot more - even indefinite) I believe it would be worthwhile.

(The argument for using a synthetic means of carbon capture is put very well here.)

This form of sequestering using trees has the advantage in that the land where the trees were planted would be available for subsequent plantation and carbon capture, whereas if just kept as forest the additional carbon capture potential after the main growth of the trees has occurred is more limited and could be subject to loss from bushfire (wood won't burn underwater!) or cut down and used in some short term product (it would be difficult to recover from deep ocean). This should limit the total amount of land that needs to be set aside for carbon sequestration activity. It would also be a great rural industry.

I would foresee millions of hectares of forests being established on existing cleared land close to a suitable coast or port. (A million hectares is a hundred square kilometres. This size of plantation is large but achievable and could be replicated in numerous locations.)

Various aspect of the scheme would need to be investigated prior to implementation. Ironbark may not be the absolute best timber for this purpose - there may be faster growing timber around - the main requirement being that it needs a density of greater than water so it would sink by itself - there are not many wood species that have this property. While I believe it would be very low, the rate of degradation of the timber in a deep ocean environment would need to be determined - however this could be done in conjunction with the initial planting - which should still be massive. A twenty year monitoring process (while the initial forest was growing) would determine if any significant degradation was to occur and also determine the best sites (a trade-off between water depth and proximity). (If it was determined that degradation was too fast nothing would have been lost - the planted ironbark forests would have still stored, and would continue to store, a lot of carbon.) Optimum age for harvest would need to be determined. The environmental impact on the ocean would have to be considered but I wouldn't foresee great adverse impact - although everything we do has some environmental impact - it is again a trade-off.

There are also systems for sequestering of carbon in the soil structure, called Terra Petra or bio char, which can occur through conversion of organic material to a form of charcoal. Apparently the carbon is then stored in the soil structure for a very long period (to 5000 years I've seen in one reference) and it has the added benefit of increasing the agricultural productivity of the soil - a win win all round.

The other approach which sounds like it might be effective is the growing of massive beds of seaweed, which are then allowed to sink to the bottom of the ocean where the carbon collected in the seaweed is effectively stored. I have heard that seaweed can grow half a metre a day and it is potentially very effective at removing carbon from seawater. My only concern is that it is removing the carbon from sea water and not directly from the air. There is massive amounts of carbon in seawater causing acidification of the oceans, so this needs to be addressed along with carbon in the atmosphere - so this process should proceed regardless. I am thinking that for seaweed to remove carbon from the atmosphere it first must be absorbed by the sea - perhaps I am wrong about this and it can absorb directly from the air - where the seaweed breaks the surface of the ocean. If it has to be absorbed by the oceans first my concern would be that the process may not be fast enough at extracting atmospheric carbon. The effect may be localised to the part of the ocean where the seaweed is - the mixing of ocean/sea water would be slower than the mixing of the gases in the atmosphere. There may also be a lag between when the carbon is removed from seawater to when this starts to decrease atmospheric carbon dioxide concentrations. The process needs to be researched. It may not be a panacea but could provide a worthwhile contribution. (Paragraph added May 2019.)

As with all schemes to address the issue of green house gas production energy and green house gas production audits need to occur to ensure there is a worthwhile benefit - from both tree absorption, seaweed and terra petra..

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