We propose to design, manufacture, and license affordable floating synthetic trees for deployment on tropical international waters such as the ITCZ.
The primary purpose of these trees is to flatten the Keeling Curve at 455 ppm by 2035 at negative cost, namely by turning a profit on the OTEC-generated power and the products that can be manufactured from carbon using that power.
This is accomplished by drawing down 3.4 ppm of CO2 a year starting in 2035, thereby fully offsetting the rate of rise of CO2 expected by then. This is to be achieved by processing 1% of the atmosphere each year (so 4.55 ppm) and capturing three-quarters of the CO2 in it (so 3.4 ppm). 1% of the atmosphere has a mass of 51.5 million million tons per year. There being 31.56 million seconds in a year, this comes to 51.5/31.56 million tons of air per second, which in round numbers (in base 6) is 68 = 1,679,616 tons per second. At 455 ppm of CO2, this much air will contain 1,160 tons of CO2, of which we propose to capture 75% or 870 tons, of which 237 tons is carbon.
Factoring 68 as 2 × 34 × 34 × 27, we propose to divide this labor among two categories of trees each assigned to 81 parties each managing 81 trees each processing 128 tons of air per second. In that second, each tree will produce 33 kg of liquid CO2 for sequestration along with 18 kg of carbon. Energy for this process is obtained by converting 84 gigawatts of ocean thermal energy to 1.76 gigawatts of mechanical energy, an efficiency of 2% typical of OTEC. Half of the latter is used to drive air down and back up the tree, leaving the remaining 880 megawatts available for industrial purposes such as extracting the carbon from the captured CO2, hydrogen from rainwater, and nitrogen from the atmosphere to make commercially attractive products built from plastics such as ABS. Each tree produces 1,560 tons of carbon a day along with enough hydrogen from rainwater and nitrogen from air to make various plastics such as polybutadiene for more trees, ABS for fans and lego bricks, etc.
One category is intended to be managed by sovereign parties to the Kyoto and Paris agreements by collaboration between our sister organization Project Davy Jones and the United Nations Framework on Climate Change. The other category is to be managed by "parties with sovereigns" as overseen by Syntrees LLC.
These synthetic trees send half of the CO2 they collect to the ocean floor. The other half is dissociated to carbon and oxygen and used to manufacture more trees as well as plastic products, sythetic fuels, etc. Prior to the invention of steam power in the 18th century, factories were built at streams where water wheels could capture the flowing stream's energy, from where their products were transported by drayage. In the proposed model, factories are built at trees, from where their products can be transported by container vessels.
Trees have sufficient manufacturing capability to manufacture more trees, which however will require only a negligible fraction of the captured CO2.
What makes a tree affordable is that it is built from materials and energy harvested from the atmosphere and the ocean and operated by a team of workers with various skills and salary rates totalling four to ten million dollars a year. Maintenance of a forest of 81 trees and their teams would therefore cost between three and eight hundred million dollars a year.
During the four years 2025-2028, The Syntrees Corporation and Project Davy Jones and will collaborate to develop trees and provide one to each of their respective 81 parties in December 2028. Each such party will then breed a forest of 80 more during the seven years 2029-2035, via a process we are still working out. Support staff provided by the party will grow in proportion to the forest.
"At scale" means not only that syntrees are many but also large. Each tree has a draft of 523 meters, a beam of 54 m in diameter at the surface, a displacement of 82 thousand tons, but a mass of only five thousand tons, primarily ABS plastic. To hold the tree vertical and mostly submerged will require 82,000 - 5,000 = 77,000 tons of ballast to hold it vertical. The nearest such ballast with the requisite density may be the ocean floor.
A synthetic tree's counterpart of a natural tree's stomata has an area of 1,024 m2, about quarter of an acre, and inhales air at 100 m/s, the speed of a 1925 Curtiss R3C biplane. The tree compresses that air isothermally at 10 ℃ to 54.6 atmospheres, captures 75% of its CO2 with a spray of liquid CO2 droplets, warms the resulting air to 22 ℃, and returns it to the surface via a series of 16 countercurrent exchange fans powering the compression phase. The role of the 84 gigawatts worth of water from each side of the main thermocline, presumed to be about 28 ℃ above and 4 ℃ below, is to maintain the down-flowing air at 10 ℃, i.e. isothermally, and the up-flowing air at 22 ℃, based on endoreversible thermodynamics. The higher temperature and pressure of the latter is the source of the surplus energy beyond that needed for compression as determined by momentum theory.
128 tons of air is 128/28.97 = 4.41 million moles. 340 ppm of this (three-quarters of 455 ppm) is 4.41*340 = 1,500 moles of captured CO2. At an enthalpy of formation of CO2 of -393 kJ/mol, 1,500*393 = 590 MJ of energy is needed to crack all of the CO2 captured by the tree per second, or 590 MW. This is two-thirds of the tree's available 880 MW.
To reduce that proportion to one-third, a suitable strategy would be to send half of the captured CO2 to the ocean floor, with a preference for benthic deserts to minimize environmental impact. This can be accomplished by piping the liquid CO2 to a depth of 3 km, requiring negligible energy. Liquid CO2 being slightly more compressible than seawater, at this depth it will sink. The Davy Jones Project reduces that proportion to zero, sending all the captured CO2 to the ocean floor save for the small amount needed to manufacture one tree per year in order to grow one starter tree to 81 trees and then maintain it at that level.
Rather than having each party choose between Davy Jones and Syntrees, it may be preferable for each party to build and maintain about 40 trees from each category. In that case, what would distinguish parties is not whether they sequester CO2 or put it to commercially attractive uses but whether they are sovereign parties operating under the aegis of the UNFCC or parties with sovereigns funded by venture capital, carbon credits, etc. This detail is one of the many things that can be worked out between now and when CO2 starts being drawn down in earnest, say by 2034.
For the purposes of legislation on the high seas, the trees of a colony might best be treated the same as ships. All trees of a colony managed by a sovereign party would fly that party's flag and be subject to its laws. Parties with sovereigns would as usual choose what country to register with.
As of March 4, 2023, a United Nations treaty on the conservation and sustainable use of BBNJ, Biodiversity Beyond National Jurisdiction, on the high seas was agreed on in New York, and adopted three months later on June 19. One of the Agreement's four themes is Area Based Management Tools (ABMT), including provision for Marine Protected Areas (MPA).
The interesting question then arises as to whether a party could stake out an area of the ITCZ on the environmental ground that it was using the area to mine the atmosphere for CO2. Would the fact that it planned to do so at a profit be a concern? This does not seem to have been a consideration in the decade or more of planning for the BBNJ.