Dead planet, living planet

ECOSYSTEM RESTORATION FOR CLIMATE CHANGE MITIGATION All living matter (biomass) – from grasses and trees to salt marshes and plankton – stores carbon. Terrestrial biomass carbon stores are often referred to as “green carbon”. Worldwide, terrestrial vegetation, soil and detritus currently store 2261 Gigatonnes of carbon (GtC; IPCC, 2007) 1 . Approximately half of terrestrial biomass carbon stocks are found in forest (IPCC, 2007). The oceans and coastal vegetation also store a large amount of carbon (often known as “blue carbon”), which is thought to be approxi- mately 38334 GtC (IPCC, 2007), though there is uncertainty about the precise quantity (Nellemann et al ., 2009).

Much recent attention has been given to the potential of eco- systems, especially forests, to take up (sequester) additional carbon and hence mitigate climate change. Unfortunately, this process is disrupted when natural ecosystems are converted for agricultural use. This releases much of the carbon stored in plants and soil, and also alters the physical and biological ef- fects of the landscape on the climate (Bala et al ., 2007). Some of these effects warm the climate, whilst others cool it. The high albedo (reflectivity) of grassland and deserts plays a role in atmospheric cooling (Hansen et al ., 1998; Thompson, 1998). High rates of evapotranspiration (release of water into the atmosphere) from tropical forest reduce surface air tem- perature and increase rainfall (Bonan, 2008). The structure of vegetation also influences the regional climate: for example, a study in Australia found that land cover change (mainly defor- 1 To illustrate how substantial these ecosystem stores of carbon are, the global annual emissions of carbon dioxide from human activity in 2004 totalled 38 Gigatonnes (IPCC 2007).2 Services include provisioning (e.g. fish and minerals), regulating (e.g. role in climate), supporting (e.g. role in water cycle) and cultural (e.g. tourism, recreation)

estation) explained up to 50% of the observed warming and changes to rainfall patterns due to reduced surface roughness (Pitman et al ., 2004). The marine environment also has a key role in climate regula- tion. The oceans store and conduct heat, while ocean chem- istry is important in regulating carbon uptake (IPCC, 2007; Reid et al ., 2009). Restoration of terrestrial and marine ecosystems therefore protects and enhances the climate regulating services of eco- systems as well as the carbon stocks that aid climate change mitigation. Many ecosystems are currently carbon sinks (they store more carbon than they lose). The IPCC Fourth Assessment (AR4) Report suggests that the size of the terrestrial sink is approxi- mately 0.5–1.5 GtC per year while the marine sink is approxi- mately 1.8–2.6 GtC per year (IPCC, 2007). However, land use change and degradation damage the terrestrial sink as well as generating carbon emissions (Ong, 1993; Anser et al ., 2005; Eliasch, 2008; Lal, 2008).

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