March 21, 2015
Sink Harvested Forests Underwater To Lower Atmospheric CO2?

Can we appreciably lower atmospheric CO2 by cutting down trees and then sinking to them to the bottom of lakes and bays? Have a look at some numbers: Canada's boreal forest stores a lot of carbon.

Stores twice as much carbon per acre as tropical rain forests. In all, Canada’s boreal forests and peatlands lock in a minimum of 229 billion tons of carbon.

Humanity emits about 34.5 billion tonnes of carbon dioxide per year.

The ton in the first paragraph is probably the North American short ton or 907.1847 kg. The metric tonne is 1000 kg. So 229 billion tons is probably 208 tonnes (unless the press release writer got their units wrong). So next lets convert tonnes of carbon dioxide to tonnes of carbon so we can compare forest carbon to yearly released atmospheric carbon. Carbon has a molecular weight of 12. Oxygen has a molecular weight of 16. So (12/(12+(2*16))) * 34.5 = 9.4 billion tonnes of carbon released into the atmosphere per year by human activity.

So if my data sources and calculations are correct so far then Canada's boreal forest contains the equivalet of about 21 years of human carbon emissions at about the current rate of emission.

Now suppose we cut down all of Canada's trees and sunk them to the bottom of lakes and Hudson's Bay. Lots of new trees would start growing up. Could they fully grow back in 21 years? If yes then we could neutralize the impact of human carbon emissions. If they would take 42 years to grow back then we'd cut the rate of increase of CO2 in the atmosphere in half. Huge impact.

Now, I'm not going to argue that cutting down all of Canada's trees all at once is a good idea. I think the climate impact of losing all those trees would be substantial and probably bad (less rain over wide areas for example). Plus, lots of birdies that spend some of their year in those forests would die. Other species probably as well.

But suppose some small percent of the trees got cut per year (and ditto in Amazon and United States and Siberia) and sunk under water. Combining across various forests we'd open up areas for more trees to grow (create holes scattered across forests) and more carbon to get pulled out of the atmosphere. In some cases just letting already cut areas return to forest would make a big impact.

Now here is where genetic engineering comes in. If we can genetically engineer crops to boost their yields we could use less space to grow crops. Then some of the current crop land could be let to return to forest. Though I suspect global population growth (especially in Africa) will prevent this from happening. Still, genetically engineered crops could at least reduce the future expansion of agriculture into more areas that are currently forests. So that would still help.

Share |      Randall Parker, 2015 March 21 10:29 AM 


Comments
Wolf-Dog said at March 23, 2015 8:25 PM:

I have read that in many cases (at least in the case of the forests in Brazil, I don't know the Canadian forests) most of the nutrients of a forest are already stored in the trees: if this is true, then cutting the trees in the forest and burying them to make room for them to regrow would dramatically hinder the regrowing phase. This is why they often burn the trees to use the ashes as fertilizer, but this would totally defeat the intended purpose of removing carbon dioxide from atmosphere.

However, if we used all these forests as fuel (both solid and liquid), then regrowing the forests would be a perfect way of recycling carbon dioxide.

Already, there are certain types of bamboo that grow 35 inches (2.916666 feet!) per day, and these are not even genetically engineered:
http://www.guinnessworldrecords.com/world-records/fastest-growing-plant/

For power generation the transportation of forests should not be significantly costlier than sending coal by train, and the advantage is that since the ashes that remain after burning the wood at power plants would be very light, sending these ashes back to the original forest location to be used as fertilizer would not add too much to the cost of carrying the wood to the power plants. And if genetic engineering is successful, it would also be possible to grow trees closer to the power plants, all over the world. If bamboo and other trees can be modified to grow in deserts, this would be a game changer, as the climate in deserts would also become better.

Ronald Brak said at March 31, 2015 7:04 PM:

Sinking biomass into deep ocean water, cold water lakes, or areas of sedimentation on continental shelves appears to be one of the cheapest methods of removing CO2 from the atmosphere and sequestering it. With oil use looking likely to fall due to the electrification of transport in coming years, using oil to power planes, ships, and perhaps long haul trucks and dumping biomass in oceans etc. to sequester the carbon released from burning oil may be considerably cheaper than using biofuels. Right now I could use this method to sequester CO2 for about $120 a tonne and I presume that by sourcing the cheapest biomass I could do if for considerably less in practice. As Wolf-Dog mentions, this will remove nutrients from the soil, but restoring nutrients would be a very small amount of the total cost of the process. I don't see room currently for huge improvements in raw biomass production resulting from genetic engineering, as it is hard to improve on the champions in this area, such as bamboo, water hyacinth, and eucalypts in Brazil. But one area where there could be significant improvements is the growing of perennial crops instead of annual crops as these plants could put energy into growing food for us year after year instead of growing new roots and stalks each year and can contribute to the build up of carbon in the soil. Of course they are not without problems such as chronic pest infestation.

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