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.
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.
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