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By Kyle Smith. The media in general, and CNN in particular, are obsessed with the photograph of a father and daughter who drowned while attempting to get across the Rio Grande. While the photo is horrible and the human suffering here is doleful to contemplate, as a political matter this photo doesn't change By Kevin D.
Hollywood movie studios have stopped making comedies. Thanks, Seth Rogen. The graph of the box-office performance of Seth Rogen comedies is a dismal sight. If the buried carbon comes out slowly over the timescale of thousands of years, it should have already passed the major peak of atmospheric CO 2 as the anthropogenic CO 2 'pulse' is absorbed into the deep ocean and the carbonate sediments Fig.
Lifetime of buried wood can be substantially longer than fossil fuel CO 2 residence time in the atmosphere. CO 2 concentration is based on a scenario in which GtC fossil fuel is burned in the next few hundred years. Depending on the burial depth, the deep roots of trees re-growing on some burial sites may eventually invade into the trench and facilitate the decomposition of buried wood so that the nutrient and carbon will slowly return to the surface and the atmosphere.
Although the vegetation could be made not to re-grow above the trench, or the buried wood could be insulated from the top soil by a layer of resistant material, re-growth might be more desirable than 'permanent' burial tens of thousands of years or longer. Thus the way wood is buried will determine the decomposition rate, and can be managed to desired effect. Long term monitoring and research of representative sites will be useful for finding optimal burying methods. One potential drawback of wood burial is that nutrient in wood will be locked away.
The same drawback also applies to other methods of large-scale vegetation use such as biofuels. This is a serious concern because nutrients may already be a limitation for plant growth in some forest ecosystems. Plants recycle a major part of the nutrient in dead material. This is especially so in the tropical rainforests where the recycling is so efficient that most of the nutrient is locked in live and dead trees rather than in the soil.
If a major fraction of the nutrient becomes locked up by buried wood, the forest growth could be severely limited after some decades so that the strategy becomes unsustainable. Here I use nitrogen as an indicator of nutrient for analysis. Fortunately for our purpose, the nutrient content in wood is much smaller than in leaves and fine roots.
For instance, typical carbon to nitrogen ratio C:N is for leaves, but for wood [ 31 , 32 ]. This is fundamentally because the structural components of plants consist mostly of lignin-cellulose complexes which are carbohydrates, i. The magnitude of this potential problem can be viewed in two ways. The fact that tropical rainforest is extremely quick at 'grabbing' whatever nutrient is on the forest floor suggests the great ability of forest at utilizing what is on the ground.
The ultimate question is whether internal fixation and external input are fast enough to compensate for the loss rate due to burial lockup. If 10 GtC y -1 of carbon is to be buried, a C:N ratio of implies that about 50 MtN y -1 Mega tonnne or 10 12 gram of nitrogen per year will be locked up in the buried wood. Although 50 MtN y -1 is a nontrivial amount, this is only a fraction of both the global natural nitrogen fixation rate of MtN y -1 and the anthropogenic N mainly from fossil fuel burning and fertilizer use deposition rate of MtN y -1 [ 33 ].
In addition, natural fixation rate may increase when nitrogen is in short supply. Thus, globally speaking, the nutrient lock-up due to burial does not appear to be a problem big enough to hold back the wood burial proposal. However, it will depend on the spatial distribution and the fraction of the nitrogen deposition that can be utilized [ 34 ]. Our current understanding of such issues is limited, and more research in this area is needed. In some regions or localities this may be a more important issue. In these cases, some moderate fertilization could be used to alleviate the problem, or the intensity of the operation could be reduced.
Dead wood, whether standing snags or down, plays an important role in forest ecology, acting as habitat for animals such as cavity-nesting birds, plants and microbial lives. To minimize the impact, it may be desirable not to completely clean the forest floor, but leave a fraction to maintain these important ecological functions. Although modern forest logging practice has shown that disturbance can be kept at minimum, there is no guarantee it will be the case when practiced world-wide. If not executed properly, it may harm forest regeneration capability, biodiversity and cause significant loss of soil carbon.
One method is to have ecological monitoring and carbon accounting conducted together by certified agencies or institutes following carefully crafted international standards. The soil carbon pool is a dynamic balance between dead vegetation input and decomposition. If the deadwood input to soil is reduced, the soil carbon pool will decrease somewhat. It is difficult to quantify this possible loss at present.
Regardless of the extent of this soil carbon loss, equilibrium will be reached after sometime so that the cumulative effect of a sustainable wood burial will eventually exceed the initial loss. Wood has been a major resource for humans ever since our ancestors learned to use fire and sticks. Current world total wood consumption is about 0. Obviously, priority will be given to these uses such as furniture and building material, but compared to the 10 GtC y -1 coarse wood production rate, there will be large additional capacity for carbon sequestration.
Indeed, the burial scheme may be carried out most naturally as an expansion of the existing logging capacity. In addition, if old furniture and building lumbers are buried rather than left to decay in open dumps, they will still serve the purpose of carbon sink.
This has already been practiced to some extent in landfills. Research is ongoing in cellulosic biofuel where cellulose in woody material is converted to fuel [ 36 ]. Should this become economical with minimum environmental impact in the future, obviously it will have priority over wood burial because of the energy produced. This can also be said for other uses such as co-firing of wood chips and agricultural residue with coal. Nevertheless, the capacity built for wood harvest and burial will lend itself naturally to collecting wood for biofuel use. The 10 GtC y -1 wood production rate also provides an approximate upper limit on how much biofuel can be produced, and the caveats discussed here such as nutrient lock-up also apply.
One possibility is that if roads are built into remote forests, it will make it easier for deforestation. What has happened in the Brazilian Amazon over the last 3—4 decades where deforestation legal and illegal follows road construction cautions against the implementation of wood harvest and burial in such regions.
For this and many other environmental concerns, a considerable fraction should be preserved and left completely natural.
Soil carbon sequestration accelerated by restoration of grassland biodiversity
A wise strategy would be intense management of suitable land to achieve higher efficiency while preserving as many forests in their natural states as possible. There may be the concern that wood burial or any other effective carbon sequestration scheme will hinder the motivation to reduce emissions and the development of alternative energy.
While this is a legitimate and important concern, there is currently a major mismatch between the urgency of the climate problem and the slow pace of the transition toward a carbon-neutral economy due to technological, economical and political hurdles. Carbon sequestration should only be used to 'buy time' so that the society has sufficient lead time to adjust while avoiding dangerous climate change. Reforestation is a widely embraced carbon sequestration technique [ 37 , 38 ].
However, its capacity in sequestering carbon is limited by competition with other land use purposes such as agriculture. In addition, as forest and underlying soil mature, the carbon sink becomes saturated. If the trees are cut or burned by fire, the stored carbon would be lost back into the atmosphere. Wood harvest and burial comes most naturally to such forests because they are by definition managed. Reforestation followed by wood burial will extend the lifetime of such land carbon sink indefinitely.
Because much marginal land suitable for reforestation is currently not utilized, the earlier such activities are undertaken, the earlier is the effect. Deforestation currently accounts for a significant fraction of the anthropogenic CO 2 emissions 0. While mid-latitude regions such as China, India, Western Europe and North America were mostly deforested in earlier centuries, current deforestation takes place mainly in the tropics, notably the Amazon and Southeast Asia.
Deforestation at the southern Amazon is typically done at the end of the dry season. Trees are cut, piled up and burned, often with the help of kerosene.
While development pressure makes deforestation difficult to stop at present, burying the downed trees instead of burning will reduce the associated CO 2 emissions at minimum cost. Such a strategy is not in defense of deforestation, but serves to reduce its negative impact. A large fraction of municipal waste is wood, e. Most of these are burned or buried in landfills where they may already have relatively long lifetime.
If these can be collected and buried in landfills with long-storage time ensured, it will serve as a carbon sink of up to 1 GtC y -1 assuming the current wood use rate [ 35 ]. This is of course part of the estimated 10 GtC y -1 world potential. One advantage of burying waste wood is that there will be no additional ecological impact, unlike wood harvest from the forest. Because it already carries significant cost to handle the waste wood, burial for carbon sequestration should be even more economically viable.
On the other hand, such wood could also be incinerated to produce energy and their costs and relative merits need to be evaluated, but the wastes do not have to be wasted anymore. Fire suppression, such as in the US and Canada over last several decades, has left a large amount of dead vegetation on the forest floor and contributed to an apparent carbon sink in North America. This additional fuel load, combined with recent drought in the America West has led to more frequent and large fires in recent years.
The release of this carbon pool through catastrophic fires may become an important source to atmospheric CO 2 in the future. Collecting dead trees and burying them would reduce fire danger while creating a carbon sink. 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, only drastically accelerated by active human management. It is ironic that the whole climate change problem is caused by the human accelerated release of the fossil fuel carbon pool.
Thus it will not be surprising if this method turns out to be the most 'natural' way to undo fossil fuel CO 2 emission. The wood burial technique uses natural tree growth to capture CO 2 from the air at nearly no cost, thus making it significantly more economical than other carbon capture methods.
For storage, past focus has been on geological formations and in the ocean. Storing carbon by wood burial under soil will not only cut down atmospheric CO 2 , but also relieve the CO 2 burden on the ocean where acidification is of major concern [ 39 ]. The traditional carbon sequestration techniques tend to be industrial scale, while the present proposal is a distributed approach. This has both advantages and disadvantages that need to be sorted out. It is likely that many of these methods will be practiced to some degree, but the merits of wood burial make it an attractive option: low tech, low cost, distributed, easy to monitor, safe, reversible, thus a no-regret strategy.
On the other hand, forest is a precious resource Mother Nature endowed upon us that serves many critical ecosystem functions and human needs. Care needs to be taken in pursuing such a strategy at large scale. Gregg, H. Qian, D. Love, R. Pavlick, A. Cohn, and B.
Shui; and the students from the Gemstone Carbon Sink team and their 'advisors' B. Zaitchik, J. Gregg, B. Cook, and S. Doug Love showed me the landfill in Greenbelt, MD. Jay Gregg proofread the manuscript. I also thank A.
Cowie and D. Nepstad for an inspirational discussion on landfill, G. Collatz, L. Heath and E. Matthews for discussion on coarse woody debris, F. Norbury for discussion on fire, and H. Sloan for explaining his logging calculator. Comments and suggestions from six anonymous reviewers helped to improve the manuscript. National Center for Biotechnology Information , U. Journal List Carbon Balance Manag v. Carbon Balance Manag.
Published online Jan 3. Ning Zeng 1. Author information Article notes Copyright and License information Disclaimer. Corresponding author. Ning Zeng: ude. Received Oct 29; Accepted Jan 3. This article has been cited by other articles in PMC. Abstract To mitigate global climate change, a portfolio of strategies will be needed to keep the atmospheric CO 2 concentration below a dangerous level. Results Carbon sequestration via wood burial: a basic assessment The possibility of carbon sequestration via wood burial stems from the observation that natural forest is typically littered with dead trees Fig.
Open in a separate window. Figure 1.
Figure 2. Figure 3. Quantifying the carbon sequestration potential 1 Sustainable sink of tree removal limited by growth rate To quantify the size of this potential carbon sink, the global dynamic vegetation and terrestrial carbon model VEGAS [ 15 , 18 , 19 ] was used. Figure 4. Table 1 Carbon sequestration potential based on coarse wood production rate GtC y -1 estimated by VEGAS assuming potential vegetation for the main regions of the world. Global Tropics Temperate Boreal 10 4. Table 2 As in Table 1, but for some sub-regions may overlap.
Table 3 A comparison of estimates of world total coarse wood production rate GtC y -1 and coarse woody debris GtC. Harmon et al. Figure 5. World distribution of coarse woody debris, in kgC m Implementation strategy The implementation of a wood burial scheme will involve three major steps: 1 Enabling access to the forest if not already in place; 2 Site selection, trench digging for burial or building a shelter for above ground storage; 3 Selective tree cutting or the collection of dead wood followed by trimming, shortening and burial or storage, repeated at an appropriate return interval.
Figure 6. Cost The scale of the climate change problem dictates that any mitigation strategy, whether being alternative energy source, carbon sequestration technique, or geo-engineering approach, has to be cost effective when operated on a large scale. Table 4 Comparison of wood burial and power plant CCS. Scale of operation Even if only half of the estimated potential 5 GtC y -1 is carried out in the next few decades, say, by , the scale of such a world-wide operation would be enormous, as illustrated in the scenario below.
Discussion Potential issues 1 Decomposition of buried wood Because of the low oxygen condition below soil surface, the decomposition of buried wood is expected to be slow. Figure 7. Synergy with other activities 1 Reforestation and afforestation: making the carbon sink long-lasting Reforestation is a widely embraced carbon sequestration technique [ 37 , 38 ]. Conclusion Coal was formed by the burial of ancient plants in anaerobic conditions such as swamp and peatland. Competing interests The author s declare that they have no competing interests.
Authors' contributions This is a single-authored paper. References IPCC.
Indirect Human Impacts Reverse Centuries of Carbon Sequestration and Salt Marsh Accretion
Climate Change. Cambridge University Press; Proceedings of the National Academy of Sciences. November 20, Special Report on Emissions Scenarios. Journal of Climate. Climatic Change.
The Economics of Climate Change. B M et al, editor. Advances in Atmospheric Sciences. Zeng N. Clim Past. Geophysical Research Letters. Global Change Biology. Environmental Protection. Agency, Washington, D. Journal of Geophysical Research-Atmospheres. FAO, the United Nations; Bulletin of the American Meteorological Society. Biogeochemistry: an analysis of global change. Global Biogeochemical Cycles. US Dept. Caldeira K, Wickett ME. Department of Energy, Oak Ridge, Tenn. Support Center Support Center. External link.
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