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13
STABILISING OR REDUCING THE AMOUNT
OF ATMOSPHERIC CARBON
Stabilising or reducing the amount of atmospheric carbon can
be achieved in essentially two ways: by reducing the rate of emis-
sion, or by increasing the rate of absorption. Any successful strat-
egy is almost certain to need both approaches, and will require
contributions from all sectors (Cowie
et al.
2007; Eliasch 2008).
Reduction in emissions can be achieved through a reduction
in fossil fuel use, in cement production or in adverse (that is
carbon-releasing) land-use change, or a combination of these.
Human needs
food
security
crop
production
livestock
feed
food
quality
fibre
purification
aquifer
recharge
filtration
water
quality
natural
archive
biodiversity
climate
change
mitigation
carbon
sequestration
CH
4
oxidation
N
2
O
reduction
desertification
control
urbanisation
habitation
recreation
infrastructure
waste
disposal
Ecosystem conservation
gene pool
reservoir
species
adaptation
ecosystem
restoration
soil quality
improvement
nature
conservation
World soil demand
Source: Lal, 2007.
Removal of carbon dioxide from the atmosphere can be
achieved either mechanically or through biological means.
Mechanical removal, referred to as carbon capture and storage
(CCS), entails the collection of CO
2
emissions from fossil fuel
at concentrated sources such as power stations and cement
plants and their storage in geological formations such as spent
oil fields (IPCC 2005). Biological mechanisms exploit the abil-
ity described above of photosynthesising organisms to capture
CO
2
and store it as biomass or as organic matter in sediments
of various kinds.
The biological management of carbon in tackling climate
change has therefore essentially two components: the reduc-
tion in emissions from biological systems and the increase in
their storage of carbon. These can be achieved in three ways:
existing stores could be protected and the current high rate of
loss reduced; historically depleted stores could be replenished
by restoring ecosystems and soils; and, potentially, new stores
could be created by encouraging greater carbon storage in ar-
eas that currently have little, for example through afforestation.
In this report, we consider the roles that natural and human-
dominated ecosystems can play in reducing emissions and in
removing carbon from the atmosphere and we refer to the lat-
ter as ‘biosequestration’.
If well designed, a biological approach to carbon management
can offer other benefits. Natural ecosystems, especially forests,
are often rich in biodiversity as well as carbon; protecting one
may serve to look after both (UNEP-WCMC 2008; Miles and
Kapos 2008); they may also offer a range of other ecosystem
services such as soil stabilisation, local climate amelioration
and recycling of waste products. Good management of these
ecosystems, and of agricultural systems, can pay dividends in
terms of water and nutrient availability and reversal of land
degradation, having positive impacts on livelihoods and help-
ing in poverty reduction (Lal 2007; Smith
et al.
2007a).
That is not to say ecosystem carbon management is straight-
forward. There are serious technical, social and economic
challenges and some risks of unintended consequences. This
report examines the state of knowledge about both its potential
and challenges.