4.3 Mitigation Options
In tropical regions there are large opportunities for C mitigation, though
they cannot be considered in isolation of broader policies in forestry, agriculture,
and other sectors. Additionally, options vary by social and economic conditions:
in some regions slowing or halting deforestation is the major mitigation opportunity;
in other regions, where deforestation rates have declined to marginal levels,
improved natural forest management practices, afforestation, and reforestation
of degraded forests and wastelands are the most attractive opportunities. However,
the current mitigative capacity11
is often weak and sufficient land and water is not always available.
Non-tropical countries also have opportunities to preserve existing C pools,
enhance C pools, or use biomass to offset fossil fuel use. Examples of strategies
include fire or insect control, forest conservation, establishing fast-growing
stands, changing silvicultural practices, planting trees in urban areas, ameliorating
waste management practices, managing agricultural lands to store more C in soils,
improving management of grazing lands, and re-planting grasses or trees on cultivated
Wood and other biological products play several important roles in carbon mitigation:
they act as a carbon reservoir; they can replace construction materials that
require more fossil fuel input; and they can be burned in place of fossil fuels
for renewable energy. Wood products already contribute somewhat to climate mitigation,
but if infrastructures and incentives can be developed, wood and agricultural
products may become a vital element of a sustainable economy: they are among
the few renewable resources available on a large scale.
4.4 Criteria for Biological Carbon Mitigation Options
To develop strategies that mitigate atmospheric CO2 and advance
other, equally important objectives, the following criteria merit consideration:
- potential contributions to C pools over time;
- sustainability, security, resilience, permanence, and robustness of the
C pool maintained or created;
- compatibility with other land-use objectives;
- leakage and additionality issues;
- economic costs;
- environmental impacts other than climate mitigation;
- social, cultural, and cross-cutting issues, as well as issues of equity;
- the system-wide effects on C flows in the energy and materials sector.
Activities undertaken for other reasons may enhance mitigation. An obvious
example is reduced rates of tropical deforestation. Furthermore, because wealthy
countries generally have a stable forest estate, it could be argued that economic
development is associated with activities that build up forest carbon reservoirs.
4.5 Economic Costs
Most studies suggest that the economic costs of some biological carbon mitigation
options, particularly forestry options, are quite modest through a range. Cost
estimates of biological mitigation reported to date vary significantly from
US$0.1/tC to about US$20/tC in several tropical countries and from US$20 to
US$100/tC in non-tropical countries. Moreover the cost calculations do not cover,
in many instances, inter alia, costs for infrastructure, appropriate discounting,
monitoring, data collection and interpretation, and opportunity costs of land
and maintenance, or other recurring costs, which are often excluded or overlooked.
The lower end of the ranges are biased downwards, but understanding and treatment
of costs is improving over time. Furthermore, in many cases biological mitigation
activities may have other positive impacts, such as protecting tropical forests
or creating new forests with positive external environmental effects. However,
costs rise as more biological mitigation options are exercised and as the opportunity
costs of the land increases. Biological mitigation costs appear to be lowest
in developing countries and higher in developed countries. If biological mitigation
activities are modest, leakage is likely to be small. However, the amount of
leakage could rise if biological mitigation activities became large and widespread.
4.6 Marine Ecosystem and Geo-engineering
Marine ecosystems may also offer possibilities for removing CO2
from the atmosphere. The standing stock of C in the marine biosphere is very
small, however, and efforts could focus, not on increasing biological C stocks,
but on using biospheric processes to remove C from the atmosphere and transport
it to the deep ocean. Some initial experiments have been performed, but fundamental
questions remain about the permanence and stability of C removals, and about
unintended consequences of the large-scale manipulations required to have a
significant impact on the atmosphere. In addition, the economics of such approaches
have not yet been determined.
Geo-engineering involves efforts to stabilize the climate system by directly
managing the energy balance of the earth, thereby overcoming the enhanced greenhouse
effect. Although there appear to be possibilities for engineering the terrestrial
energy balance, human understanding of the system is still rudimentary. The
prospects of unanticipated consequences are large, and it may not even be possible
to engineer the regional distribution of temperature, precipitation, etc. Geo-engineering
raises scientific and technical questions as well as many ethical, legal, and
equity issues. And yet, some basic inquiry does seem appropriate.
In practice, by the year 2010 mitigation in land use, land-use change, and
forestry activities can lead to significant mitigation of CO2 emissions.
Many of these activities are compatible with, or complement, other objectives
in managing land. The overall effects of altering marine ecosystems to act as
carbon sinks or of applying geo-engineering technology in climate change mitigation
remain unresolved and are not, therefore, ready for near-term application.