The human ecology of climate change - Climate Change: Biological and Human Aspects - page 431

Croplands
5%

Tropical forests
17%

Wetlands
10%

Tundra
5%

Temperate
forests
6%

Deserts and
semi-deserts
8%

Temperate
grasslands
12%

Boreal forests
24%

Tropical
savannahs
13%

Fig. 7.15 Theproportionsofsome2.3Ttoftotalglobalcarbonstocksinsoilandvegetationindiferentterrestrial

biomes.AfterRoyalSociety(2001).

turned into other forms of carbon, such as methane. Another theoretical problem
of this hypothetical situation would be that actually drawing down that much carbon
would serve to draw carbon out of the oceans. This is one reason why the atmospheric
residence time of adding a single molecule of carbon dioxide to the atmosphere is
effectively between 50 and 200 years (see Table 1.1). Nonetheless, the idea of trapping
(sequestering) carbon in biomass and soils is intriguing. Indeed, we know that roughly
half the carbon released into the atmosphere through human action each year remains
in the atmosphere. The other half is absorbed by vegetation, soils and the oceans, so
sequestration already takes place somewhere in the biosphere.
The possibility that forests and soils might be deliberately manipulated to mitigate
carbon dioxide emissions was recognised by the UN's Framework Convention on
Climate Change (FCCC) in 1992 and the Kyoto Protocol (1997). (The convention
and protocol will be discussed further in the next chapter.) Both emphasise natural
terrestrial sinks rather than marine ones, largely because land carbon is easier to
manipulate and also because of issues of ownership.
There is very roughly 2.3 Tt of carbon in vegetation and soils (and a further 1 Tt
in the oceans' surface layers, to which we will return later): this is very much an
approximate park figure for discussion purposes (see Figure 1.3). However, carbon is
not distributed equally across terrestrial biomes (categories of regional communities
of species). This is not only because some biomes contain more carbon per unit
area than others but because some biomes are more extensive globally than others.
Figure 7.15 provides a proportional breakdown showing in which terrestrial biomes
the carbon can be found.
Forests and forest soils contain about 47% of terrestrial-biome carbon and so
this form of carbon storage is attracting considerable attention. However, broadly
speaking, forests that have been in existence for thousands of years (climax forest