Abstract
Abstract. The response of the terrestrial carbon cycle to future changes in climate and atmospheric CO2 is assessed by analysing simulation results for the 2006–2100 period made with the second generation Canadian Earth system model (CanESM2) for the RCP 2.6, RCP 4.5 and RCP 8.5 climate change scenarios. Our interest is in the extent to which global terrestrial carbon pools and sinks, in particular those of the Amazonian region, are vulnerable to the adverse effects of climate change. CanESM2 results indicate that land remains an overall sink of atmospheric carbon for the 2006–2100 period. The net carbon uptake by land in response to changes in climate and atmospheric CO2 is close to 20, 80 and 140 Pg C for the RCP 2.6, 4.5 and 8.5 scenarios, respectively. The latitudinal structure of future atmosphere–land CO2 flux remains similar to that observed for the historical period with northern mid- to high-latitude regions gaining carbon from the atmosphere while the tropics remain either carbon neutral or a modest source of atmospheric carbon depending on scenario. These changes occur in conjunction with simulated precipitation and soil moisture increases over northern mid- and high-latitude land regions and precipitation and soil moisture decreases over the South American continent in all scenarios. Compared to other regions of the globe, which are either carbon sinks or near neutral, the Amazonian region is simulated to be a net source of carbon during the 21st century. Moreover, and unexpectedly, the rate of carbon loss to the atmosphere from the Amazonian region is largely independent of the differences between the three scenarios considered.
Highlights
The uptake of carbon dioxide by the land and ocean since the start of the industrial era has moderated the rate of increase of atmospheric CO2 that would have otherwise occurred as a consequence of anthropogenic fossil fuel and land use change emissions (Canadell et al, 2007; Le Quéré et al, 2013)
Terrestrial ecosystems will respond to future changes in climate as well as to changes in atmospheric CO2 concentration, nitrogen deposition rates, and anthropogenic land use change (LUC)
Earth system models (ESMs), which include representations of terrestrial and oceanic carbon cycle processes, provide a tool with which to study the response of terrestrial ecosystems to possible future changes in climate and atmospheric CO2 concentration
Summary
The uptake of carbon dioxide by the land and ocean since the start of the industrial era has moderated the rate of increase of atmospheric CO2 that would have otherwise occurred as a consequence of anthropogenic fossil fuel and land use change emissions (Canadell et al, 2007; Le Quéré et al, 2013). Terrestrial ecosystems will respond to future changes in climate as well as to changes in atmospheric CO2 concentration, nitrogen deposition rates, and anthropogenic land use change (LUC). Earth system models (ESMs), which include representations of terrestrial and oceanic carbon cycle processes, provide a tool with which to study the response of terrestrial ecosystems to possible future changes in climate and atmospheric CO2 concentration. We analyse results from simulations made with the second generation Canadian Earth system model (CanESM2) in order to investigate terrestrial ecosystem response to the changes in climate and atmospheric CO2 concentration consistent with three future climate change scenarios. We focus on the behaviour of the terrestrial carbon cycle in general and on the Amazonian region in particular where the simulated reduction in precipitation transforms the region from a sink of atmospheric carbon over the historical period to a source of atmospheric carbon during the 21st century
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