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
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.
Update December 2019 - one of the concerns about this approach is the prevalence of bushfires (wildfires) and also drought now. Perhaps a planted forest like suggested may not be able to reliably grow for twenty year without it being impacted by fire and/or drought.
There are also systems for sequestering of carbon in the soil
structure, called biochar,
which can occur through conversion of organic material to a form
of charcoal. Apparently the carbon can then be 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.
Update May 2019: - 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.
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.
Update - December 2019: I first heard about biochar many years ago. I heard about the use of seaweed over six months ago - a Tim Flannery documentary. This is what frustrates and annoys me. There are these apparent good ideas and processes already known about that if implemented could be significant in the processes for the reduction of carbon dioxide. But there is no large scale development, no up scaling of the processes that I hear about. For biochar there was talk that it could be used to process agricultural waste products. So it was not a matter of having to plant a new crop specifically for converting to biochar. Perhaps the process could be used to convert domestic organic household waste to biochar. But no - nothing happens. Carbon dioxide level keep rising, scientists keep telling politicians that this is a significant problem, temperature measurements keep breaking record, animals and insect species keep going extinct or becoming threatened and scientists keep warning of the likely flow on consequences from this, weather events such as droughts and the flow on fire events, cyclones and the heat waves have become so frequent that it must be obvious to anybody who cares to think about it for a couple of seconds that climate change is not just a theoretical construct that may occur in the future but an everyday reality for our world. And yet our country's and other countries' response to it is as if it is not all that serious and that there is still plenty of time. The response is slower than the rate at which the glaciers and other ice sheets are melting. It is beyond my comprehension.
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