Net biome production of the Amazon Basin in the 21st century

Abstract

Global change includes multiple stressors to natural ecosystems ranging from direct climate and land-use impacts to indirect degradation processes resulting from fire. Humid tropical forests are vulnerable to projected climate change and possible synergistic interactions with deforestation and fire, which may initiate a positive feedback to rising atmospheric CO 2 . Here, we present results from a multifactorial impact analysis that combined an ensemble of climate change models with feedbacks from deforestation and accidental fires to quantify changes in Amazon Basin carbon cycling. Using the LPJmL Dynamic Global Vegetation Model, we modelled spatio-temporal changes in net biome production (NBP); the difference between carbon fluxes from fire, deforestation, soil respiration and net primary production. By 2050, deforestation and fire (with no CO 2 increase or climate change) resulted in carbon losses of 7.4-20.3 Pg C with the range of uncertainty depending on socio-economic storyline. During the same time period, interactions between climate and land use either compensated for carbon losses due to wetter climate and CO 2 fertilization or exacerbated carbon losses from droughtinduced forest mortality (À20.1 to 1 4.3 Pg C). By the end of the 21st century, depending on climate projection and the rate of deforestation (including its interaction with fire), carbon stocks either increased (1 12.6 Pg C) or decreased (À40.6 Pg C). The synergistic effect of deforestation and fire with climate change contributed up to 26-36 Pg C of the overall decrease in carbon stocks. Agreement between climate projections (n 5 9), not accounting for deforestation and fire, in 2050 and 2098 was relatively low for the directional change in basin-wide NBP (19-37%) and aboveground live biomass (13-24%). The largest uncertainty resulted from climate projections, followed by implementation of ecosystem dynamics and deforestation. Our analysis partitions the drivers of tropical ecosystem change and is relevant for guiding mitigation and adaptation policy related to global change.

Present state of global wetland extent and wetland methane modelling: conclusions from a model inter-comparison project (WETCHIMP)

“…NPP enhancement is a strong lever on CH 4 emissions, as ORCHIDEE's strong NPP enhancement under elevated [CO 2 ] partially explains its strong increase in global wetland CH 4 emissions. This pattern in NPP response has been reported previously (for the LPJ model) (Hickler et al, 2008;Poulter et al, 2010). CLM4Me has the opposite pattern with a three-times stronger response from the extratropics.…”

The global carbon budget 1959–2011

“…Four different DGVM estimates are presented here and used to explore the uncertainty in LUC annual emissions (Jain et al, 2013;Kato et al, 2013;Poulter et al, 2010;Stocker et al, 2011). While many published DGVM LUC emissions estimates exist, these model runs were driven by a consistently updated HYDE LUC dataset up to year 2009.…”

The importance of tree demography and root water uptake for modelling the carbon and water cycles of Amazonia

“…Future changes in the rate of carbon sequestered by Amazonia could potentially lead the global climate system to a critical tipping point (Ahlström et al, 2017;Lenton et al, 2008;Nobre and Borma, 2009), and trigger positive carbon cycle climate feedbacks from forest dieback. Yet, large uncertainties impede the production of robust future projections of changes in net 5 carbon uptake over Amazonia (Arora et al, 2013;Jones et al, 2013;Poulter et al, 2010) -current model projections range from no change, or an increase in tree biomass production Huntingford et al, 2013;Rammig et al, 2010), to large-scale Amazonian dieback (Cox et al, 2004;Good et al, 2011). …”