The Natural Fix?

The world’s terrestrial ecosystems are a vast store of carbon con-

taining more than 2000 Gt C and are acting as a net sink of ap-

proximately 1.5 Gt C per year, of which tropical forests account

for a large proportion (Luyssaert

et al.

2007; IPCC 2007b).

Sequestration at these levels would be equivalent to a 40–70

ppm reduction of CO

e in the atmosphere from anthropogenic

emissions by 2100 (Canadell and Raupach 2008).

Aswell asmaintaining these stores and sinks, there is significant po-

tential for reducing future emissions of greenhouse gases through

restoring degraded environments, for example through re-wetting

peatlands and re-planting forests in areas that have been deforested,

and reducing the rates of deforestation and loss of peatlands.

Without implementation of effective policies andmeasures to slow

deforestation, clearing of tropical forests is likely to release an addi-

tional 87 to 130 Gt C by 2100, corresponding to the carbon release

of more than a decade of global fossil fuel combustion at current

rates (Houghton 2005b; Gullison

et al.

2007). Of course if defor-

estation could be eliminated, these emissions would be avoided.

However, even using more conservative assumptions for reduc-

tions in deforestation (deforestation rates observed in the 1990s

decline linearly from 2010–50 by 50%, and deforestation stops

altogether when 50% of the area remains in each country that was

originally forested in 2000), a cumulative emission reduction of

50 Gt C could be achieved by 2100 (Gullison

et al.

2007).

Peatlands are another ecosystem that offers great potential for

reducing future emissions. It is estimated that 65 million ha of

the global peatland resource is currently degraded, largely as a

result of drainage. Peat oxidation from this area is believed re-

sponsible for annual carbon emissions of about 0.8 Gt, equiva-

lent to 20% of the total net 2003 greenhouse gas emissions of

the Annex 1 Parties to the UNFCCC. Peat fires in Southeast

Asia (primarily Indonesia) are responsible for half of these

global peatland emissions (Parish

et al.

2008).

SUMMARY – NATURAL ECOSYSTEMS

Tundra

Boreal

Forest

Temperate

Forest

Temperate

grassland

Desert

and dry

shrublands

Savannas

and tropical

grasslands

Tropical

forests

Peatlands

Oceans and

coasts

Vegetation

growth

Slow

Fast

Intermediate

Slow

Fast

Slow

In terms of

plankton: Fast

Vegetation

decomposition

Slow

Fast

Slow

Fast

Slow

Fast

C Source

or Sink

Sink

Likely sink

Sink (but

uncertain)

Sink

Current C storage

(t C / ha)

Approx. 258

Soil: 116–343;

Vegetation: 61–93

156–320

Soil: 133;

Vegetation: 8

Desert soil: 14–102;

Dryland soil: < 266;

Vegetation: 2–30

Soil: < 174;

Vegetation: < 88

Soil: 94–191;

Vegetation: 170–250

1450

(Total)

Surface: 1020 Gt C;

DOC: 700 Gt C;

Deep ocean: 38100;

Sediments: 150

Where majority of

C is stored

Permafrost

Soil

Biomass above-

and below-ground

Soil

Aboveground

vegetation

Soil

Deep ocean

Main threat(s) for

potential C emission

Rising temperatures

Fires, logging, mining

Historic losses high but

largely ceased

Historic losses high but

largely ceased

Land degradation

Fire with subsequent

conversion to pasture or

grazing land

Deforestation and forest

degradation

Drainage, conversion, fire

Not emission but

decreasing uptake

capacity

Carbon in natural ecosystems