The Natural Fix?

SUMMARY – NATURAL ECOSYSTEMS

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 2 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).

Carbon in natural ecosystems

Vegetation growth

Vegetation decomposition

C Source or Sink

Current C storage (t C / ha) Approx. 258 Soil: 116–343; Vegetation: 61–93 156–320

Where majority of C is stored Permafrost Soil Biomass above- and below-ground Soil

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

Tundra Boreal Forest Temperate Forest Temperate grassland Desert and dry shrublands Savannas and tropical grasslands Tropical forests Peatlands Oceans and coasts

Slow Slow

Slow Slow

Sink Sink

Fast

Fast

Sink

Intermediate

Slow

Likely sink

Soil: 133; Vegetation: 8

Slow

Slow

Sink (but uncertain)

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

Soil

Fast

Fast

Sink

Soil

Fast

Fast

Sink

Aboveground vegetation Soil Deep ocean

Slow In terms of plankton: Fast

Slow Fast

Sink Sink

Not emission but decreasing uptake capacity

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