Global CO2 Flows, Carbon Reservoirs, and Reservoir Changes

Figure 2 portrays estimated sizes of the earth's carbon reservoirs, average annual changes in the amount of carbon held in the reservoirs, and recent flows of CO₂ between land and ocean reservoirs and the atmosphere.


Figure 2

Note: Tan colored pool is decreasing in size. Blue colored pools are increasing. Intensity of blue indicates magnitude of stock change. Numbers in red indicate estimated total amount of carbon in reservoir. Numbers in green indicate average annual change in amount of carbon in reservoir. Gigatons (Gt) = 109 metric tons. Sources: Bolin et al. in IPCC, 2000a; Houghton, 1997.

As shown in Figure 2, the annual average human-induced flows of CO₂ - 6.3 gigatons (Gt) from fossil-fuel combustion and 1.6 Gt from deforestation in the 1990s - are a small fraction of total CO₂ flows. However, these flows are resulting in increased carbon in the ocean and atmospheric reservoirs.

Anthropogenic emissions of CH₄ and N₂O comprise a much larger share of total emissions of these gases than is the case for CO₂. Approximately 70 percent of the 550 million metric tons (MMT) of CH₄ emitted annually and about half of the 14 MMT of N₂O emitted annually are due to human activities (Bolin et al. in IPCC, 2000a).