THE IMPACTS OF FUTURE
CLIMATE CHANGE ON
ECOSYSTEM CARBON
Climate change has a major impact on the factors governing the uptake and storage of
carbon by ecosystems and therefore plays a key role in the future capacity of ecosystems
to sequester carbon.
TERRESTRIAL
Research results from Amazonian and African tropical forests leading to carbon being released more quickly back into the atmo-
show that carbon storage per hectare has increased over the past sphere (respiration) (Heath et al. 2005; Davidson and Janssens
few decades, possibly as a result of higher concentrations of carbon 2006). Higher autumn respiration rates and resulting soil carbon
dioxide in the atmosphere (Phillips et al. 2008; Lewis et al. 2009). loss may turn boreal forest areas into carbon sources (Piao et al.
An increase in vegetation biomass is accompanied by an increase 2008). Fertilization experiments in Alaska showed that while an-
in plant-derived carbon input into soils from leaf and root detritus nual aboveground plant growth doubled, the loss of carbon and
(Davidson and Janssens 2006). Beyond this, “new” carbon sinks nitrogen from deep soil layers more than offset this increased stor-
may appear in the arctic and at high altitudes if temperature in- age of carbon in plant biomass (Mack et al. 2004). Other factors
creases allow vegetation to grow here (Schaphoff et al. 2006). associated with climate change may turn carbon sinks to sources,
for example the thawing of permafrost in northern ecosystems
However, a range of models for future changes in biological car- (Gruber et al. 2004; Johansson et al. 2006; Schuur et al. 2008),
bon sequestration project that terrestrial ecosystems will serve as an increase in ozone levels inhibiting photosynthesis (Felzer et al.
a carbon sink only until 2050. After that, they may become car- 2005) and changing hydrologic regimes contributing to tropical
bon saturated or in the worst case start to act as carbon sources forest dieback (Fung et al. 2005; Hutyra et al. 2005; Nepstad et al.
towards the end of the 21st century (White et al. 2000; Cox et al. 2007; Huntingford et al. 2008). The serious drought of the year
2000; Cramer et al. 2001; Joos et al. 2001; Lenton et al. 2006; 2005 that hit the Amazon rainforest, for instance, resulted in con-
Schaphoff et al. 2006). Several factors related to climate change siderable losses of carbon from aboveground biomass, estimated
have been found to counteract an overall increase in carbon up- as in the range of 1.2 to 1.6 Gt (Phillips et al. 2009). Moreover,
take and storage by ecosystems, especially in coaction with other the species composition of tropical forests is likely to change with
drivers of ecosystem degradation (e.g. Nepstad et al. 2008): An changing climate, and this may have considerable impact on their
increase in temperature accelerates soil carbon decomposition carbon storage capacity (Bunker et al. 2005).
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