Overview

The terrestrial biosphere takes up 60 GtC (Gigaton carbon) per year via photosynthesis, while the phytoplanktons in the ocean absorb almost as much. The carbon assimilated on land is allocated to three major carbon pools: leave, root, wood. As leaves fall and trees die, they are decomposed by bacteria, fungi, insects and animals, and eventually the carbon goes back to the atmosphere on the timescale of a season to hundreds of years. As a result the net carbon exchange between the atmosphere and the biosphere is nearly zero. This is part of the so-called 'fast carbon cycle', compared to the 'slow carbon cycle' which determines fossil fuel formation on geological timescales. Modifying the fast carbon cycle is usually considered not effective at directly influencing the atmospheric CO2 which is controlled by the slow imbalance of the geological reservoirs.

However, 60 GtC/y is a large flux compared to the current fossil fuel emission rate of 8 GtC/y. If we can 'siphon' only a fraction of this fast carbon cycle and store it away semi-permanently via active human management, we may be able to sequester a significant amount of carbon to counter global warming. In this respect, all the biospheric carbon sequestration proposals falls in this category. Some of them are briefly discussed below in two steps: carbon carrier and storage method.

Carbon Carriers

Wood

  Wood is preferable to leafs and roots because its lignin-cellulose structure gives it several advantages including resistance to decay and less nutrient loss. Estimates suggest a 10 GtC/y in the form of coarse wood is produced in the world's forests. The practical potential may be 1-5 GtC/y. However, the wood needs to be harvested via collection of dead wood or selective cutting in a way such that the forest is least disturbed.

Crop Residue

  Crop residue could be partially harvested and stored. It is estimated that there may be about 1 GtC/y from the world's agriculture.

Biochar

  A process called pyrolysis, heating without oxygen, can convert essentially any biomass into char, a reduced and very stable form of carbon.

Planktons and fish

Dead planktons and fish fall to the bottom of the ocean, and some of them eventually get buried in the sediment. The carbonates carried in shells and bones, though inorganic, are biologically produced. A small fraction of organic matter buried this way eventually becomes oil. The productivity of the ocean is mostly limited by nutrient, so artificially increasing nutrients such as iron can increase the productivity, and possibly increasing carbon burial rate.

Storage methods

Bury under soil

    Under a sufficiently thick layer of soil oxygen would be quickly deplected, thus preventing decomposition. Coal was formed by the burial of ancient plants in anaerobic conditions such as swamp and peatland. The proposed wood burial method is essentially a first step of a fossil fuel formation process.

Bury under water: ocean, lakes and wetland

    Oxygen is generally depleted under water compared to in the air, thus would also slow down decomposition. In particular, peats accumulate in wetland.

Store in above-ground shelters

  This has the advantage of saving the carbon and energy stored in these 'carbon/energy banks' and they can be used more easily than burial if future bioenergy technologies such as large-scale cellulosic ethanol and advanced wood combustion become economical and environmentally sound.

Mixing of biochar in soil

  Enhance soil's ability in retaining water and nutrient, and if not decomposed, also stores carbon.

References

Dyson, F. J.: "Can We Control Carbon Dioxide in the Atmosphere?" Energy 2, 287-291 1977. (The original paper in which physicist Freeman Dyson proposed that fast-growing trees planted on a land area approximately the size of the US could temporarily offset our fossil fuel emissions)

Dyson, F. J. and Marland, G.: 1979, Technical Fixes for Climatic Effects of CO2 in Workshop on the Global Effects of Carbon Dioxide from Fossil Fuels, 1977, Rep. CONF-770385, US. Dept. of Energy. Washington D.C., pp. 111-118. (A summary of many earlier ideas of engineering responses to climate change including several biological carbon sequestration methods)

Lehmann, J., Gaunt, J., and Rondon, M.: Bio-char sequestration in terrestrial ecosystems – a review, Mitigation and Adaptation Strategies for Global Change, 11, 403–427, 2006.

Metzger RA, Benford G: Sequestering of atmospheric carbon through permanent disposal of crop residue. CLIMATIC CHANGE 49 (1-2): 11-19 APR 2001.

Scholz, F., U. Hasse, Permanent Wood Sequestration: The Solution to the Global Carbon Dioxide Problem, ChemSusChem, 2008, DOI: 10.1002/cssc.200800048.
 

Zeng, N., 2008: Carbon sequestration via wood burial. Carbon Balance and Management, 3:1; doi:10.1186/1750-0680-3-1. Download from [CBM]

Notes

The purpose of this website is to bring together collaborators from many different fields to discuss sequestration of carbon in various parts of the biosphere. Many of the means that have been suggested to reduce atmospheric carbon, to lessen the impact of global climate change, rely upon enhancing uptake of carbon from the atmosphere using photosynthetic organisms. These organisms absorb carbon during their lives, but much of this carbon is returned to the atmosphere when these organisms die. Hence, to create a permanent sink that will sequester the carbon from the atmosphere over a long time scale, some of this organic matter must not be allowed to decay.  Ideas of how to accomplish this include reforesting areas that have been clear cut, burial of biomass underground or under water, storage of biomass in above-ground shelters, increasing the amount of carbon in agricultural soils, and increasing photosynthetic activity in the world's oceans by fertilization with nutrients such as iron.

These topics span a broad range of disciplines including atmospheric science, forestry, oceanography, agriculture and biology.  Because no one person can be an expert in all these areas, it is our hope that this site can serve as a place for experts in the individual disciplines to come together and share their knowledge in their area of expertise. Each means that has been suggested for sequestering carbon in the biosphere listed above has its own discussion board, where experts can debate important aspects of how such a plan for carbon sequestration would be carried out. Opinions and ideas generated will be summarized in articles that are constantly updated and disseminated to the scientific community, the public, the media, governments, NGOs and other stakeholders.

Thank you for visiting our site, hopefully together we can find the most practical means of helping to solve the climate crisis through utilization of the biosphere.