Historical carbon dioxide emissions caused by land-use changes are possibly larger than assumed

Arneth, Almut; Sitch, Stephen; Pongratz, Julia; Stocker, Benjamin D.; Ciais, Philippe; Poulter, Benjamin; Bayer, A.; Bondeau, Alberte; Calle, Luz Marina; Chini, L. P.; Gasser, Thomas; Fader, Marianela; Friedlingstein, Pierre; Kato, Etsushi; Li, W.; Lindeskog, Mats; Nabel, Julia E. M. S.; Pugh, Thomas A. M.; Robertson, Eddy; Viovy, Nicolas; Ye, Chao; Zaehle, Sönke

doi:10.1038/ngeo2882

Cited by 349 publications

(304 citation statements)

References 68 publications

(31 reference statements)

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“…In the ORCHIDEE model, increasing CO 2 leads to a fertilization effect as it increases the NPP and results in an increase in biomass production on land for most PFTs, depending on the temperature and moisture conditions (Arneth et al, 2017;Piao et al, 2009). Figure 9 shows the contribution of this fertilization effect to the cumulative SOC stock change during 1850-2005 (S4-S8), which is in the same order of magnitude as the effect of LUC excluding soil erosion.…”

Section: Effects Of Atmospheric Co 2 Increasementioning

confidence: 61%

Global soil organic carbon removal by water erosion under climate change and land use change during AD 1850–2005

et al. 2018

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Abstract. Erosion is an Earth system process that transports carbon laterally across the land surface and is currently accelerated by anthropogenic activities. Anthropogenic land cover change has accelerated soil erosion rates by rainfall and runoff substantially, mobilizing vast quantities of soil organic carbon (SOC) globally. At timescales of decennia to millennia this mobilized SOC can significantly alter previously estimated carbon emissions from land use change (LUC). However, a full understanding of the impact of erosion on land-atmosphere carbon exchange is still missing. The aim of this study is to better constrain the terrestrial carbon fluxes by developing methods compatible with land surface models (LSMs) in order to explicitly represent the links between soil erosion by rainfall and runoff and carbon dynamics. For this we use an emulator that represents the carbon cycle of a LSM, in combination with the Revised Universal Soil Loss Equation (RUSLE) model. We applied this modeling framework at the global scale to evaluate the effects of potential soil erosion (soil removal only) in the presence of other perturbations of the carbon cycle: elevated atmospheric CO 2 , climate variability, and LUC. We find that over the period AD 1850-2005 acceleration of soil erosion leads to a total potential SOC removal flux of 74 ± 18 Pg C, of which 79 %-85 % occurs on agricultural land and grassland. Using our best estimates for soil erosion we find that including soil erosion in the SOC-dynamics scheme results in an increase of 62 % of the cumulative loss of SOC over 1850-2005 due to the combined effects of climate variability, increasing atmospheric CO 2 and LUC. This additional erosional loss decreases the cumulative global carbon sink on land by 2 Pg of carbon for this specific period, with the largest effects found for the tropics, where deforestation and agricultural expansion increased soil erosion rates significantly. We conclude that the potential effect of soil erosion on the global SOC stock is comparable to the effects of climate or LUC. It is thus necessary to include soil erosion in assessments of LUC and evaluations of the terrestrial carbon cycle.

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Section: Effects Of Atmospheric Co 2 Increasementioning

confidence: 61%

Global soil organic carbon removal by water erosion under climate change and land use change during AD 1850–2005

et al. 2018

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“…In a recent review (Prestele et al, 2017), proper representation of gross LUC or sub-grid bidirectional land turnover has been identified as one of the three major challenges in implementing LUC in DGVMs for credible climate assessments, despite that these have already been pioneered by some models (Table 1). Large underestimation of LUC emissions would occur when gross LUC is ignored, as is shown by several model results reviewed in Arneth et al (2017).…”

Section: Discussionmentioning

confidence: 99%

“…All models in Table 1 include shifting cultivation and wood harvest except that shifting cultivation is not included in ISAM, and five of them include sub-grid secondary land tiles when accounting for LUC. A recent review by Arneth et al (2017) found that including processes that have been previously neglected in DGVMs, including gross transitions and other land management processes such as crop harvest and management, can lead to an upward shift of estimated LUC emissions. Their study thus highlights the importance of including these processes.…”

mentioning

confidence: 99%

Representing anthropogenic gross land use change, wood harvest, and forest age dynamics in a global vegetation model ORCHIDEE-MICT v8.4.2

Ciais

Luyssaert

et al. 2018

Geosci. Model Dev.

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Abstract. Land use change (LUC) is among the main anthropogenic disturbances in the global carbon cycle. Here we present the model developments in a global dynamic vegetation model ORCHIDEE-MICT v8.4.2 for a more realistic representation of LUC processes. First, we included gross land use change (primarily shifting cultivation) and forest wood harvest in addition to net land use change. Second, we included sub-grid evenly aged land cohorts to represent secondary forests and to keep track of the transient stage of agricultural lands since LUC. Combination of these two features allows the simulation of shifting cultivation with a rotation length involving mainly secondary forests instead of primary ones. Furthermore, a set of decision rules regarding the land cohorts to be targeted in different LUC processes have been implemented. Idealized site-scale simulation has been performed for miombo woodlands in southern Africa assuming an annual land turnover rate of 5 % grid cell area between forest and cropland. The result shows that the model can correctly represent forest recovery and cohort aging arising from agricultural abandonment. Such a land turnover process, even though without a net change in land cover, yields carbon emissions largely due to the imbalance between the fast release from forest clearing and the slow uptake from agricultural abandonment. The simulation with sub-grid land cohorts gives lower emissions than without, mainly because the cleared secondary forests have a lower biomass carbon stock than the mature forests that are otherwise cleared when sub-grid land cohorts are not considered. Over the region of southern Africa, the model is able to account for changes in different forest cohort areas along with the historical changes in different LUC activities, including regrowth of old forests when LUC area decreases. Our developments provide possibilities to account for continental or global forest demographic change resulting from past anthropogenic and natural disturbances.

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“…Arneth et al (2017) reviewed the "missing processes" in LULCC modelling with DGVMs and found that ignoring gross LULCC could underestimate the global E LULCC by 36 Pg C on average over the historical period . In this study, we used a bookkeeping method to quantify the difference in LULCC emissions calculated using net versus gross forest area transitions and to show the existence of critical ratios of gross to net forest area changes above which land-use action will cause a reversed sign of cumulative carbon flux.…”

Section: Discussionmentioning

confidence: 99%

“…Because of the non-symmetrical dynamics of CO 2 fluxes between forest loss and gain, E LULCC differs between net and gross area changes. Arneth et al (2017) recently reviewed this issue using DGVMs and concluded that considering gross LULCC significantly increased the simulated E LULCC on a global scale. Gross land-use and land-cover area transition datasets including, for example, shifting cultivation practice (Hurtt et al, 2011) and reconstructions using empirical ratios between gross and net transitions (Fuchs et al, 2015) are now available and have been implemented in a bookkeeping model (Hansis et al, 2015) as well as in some DGVMs to improve the estimate of E LULCC (Fuchs et al, 2016;Shevliakova et al, 2009;Stocker et al, 2014;Wilkenskjeld et al, 2014;Yue et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Gross changes in forest area shape the future carbon balance of tropical forests

Li¹,

Ciais²,

Ye³

et al. 2018

Biogeosciences

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Abstract. Bookkeeping models are used to estimate land-use and land-cover change (LULCC) carbon fluxes (E LULCC ). The uncertainty of bookkeeping models partly arises from data used to define response curves (usually from local data) and their representativeness for application to large regions. Here, we compare biomass recovery curves derived from a recent synthesis of secondary forest plots in Latin America by Poorter et al. (2016) with the curves used previously in bookkeeping models from Houghton (1999) and Hansis et al. (2015). We find that the two latter models overestimate the long-term (100 years) vegetation carbon density of secondary forest by about 25 %. We also use idealized LULCC scenarios combined with these three different response curves to demonstrate the importance of considering gross forest area changes instead of net forest area changes for estimating regional E LULCC . In the illustrative case of a net gain in forest area composed of a large gross loss and a large gross gain occurring during a single year, the initial gross loss has an important legacy effect on E LULCC so that the system can be a net source of CO 2 to the atmosphere long after the initial forest area change. We show the existence of critical values of the ratio of gross area change over net area change (γ A gross A net ), above which cumulative E LULCC is a net CO 2 source rather than a sink for a given time horizon after the initial perturbation. These theoretical critical ratio values derived from simulations of a bookkeeping model are compared with observations from the 30 m resolution Landsat Thematic Mapper data of gross and net forest area change in the Amazon. This allows us to diagnose areas in which current forest gains with a large land turnover will still result in LULCC carbon emissions in 20, 50 and 100 years.

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Historical carbon dioxide emissions caused by land-use changes are possibly larger than assumed

Cited by 349 publications

References 68 publications

Global soil organic carbon removal by water erosion under climate change and land use change during AD 1850–2005

Global soil organic carbon removal by water erosion under climate change and land use change during AD 1850–2005

Representing anthropogenic gross land use change, wood harvest, and forest age dynamics in a global vegetation model ORCHIDEE-MICT v8.4.2

Gross changes in forest area shape the future carbon balance of tropical forests

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