Are terrestrial biosphere models fit for simulating the global land carbon sink?

Although the existence of a large carbon sink in terrestrial ecosystems is well-established, the drivers of this sink remain uncertain. It has been suggested that perturbations to forest demography caused by past land-use change, management, and natural disturbances may be causing a large component of current carbon uptake. Here we use a global compilation of forest age observations, combined with a terrestrial biosphere model with explicit modeling of forest regrowth, to partition the global forest carbon sink between old-growth and regrowth stands over the period 1981–2010. For 2001–2010 we find a carbon sink of 0.85 (0.66–0.96) Pg year−1located in intact old-growth forest, primarily in the moist tropics and boreal Siberia, and 1.30 (1.03–1.96) Pg year−1located in stands regrowing after past disturbance. Approaching half of the sink in regrowth stands would have occurred from demographic changes alone, in the absence of other environmental changes. These age-constrained results show consistency with those simulated using an ensemble of demographically-enabled terrestrial biosphere models following an independent reconstruction of historical land use and management. We estimate that forests will accumulate an additional 69 (44–131) Pg C in live biomass from changes in demography alone if natural disturbances, wood harvest, and reforestation continue at rates comparable to those during 1981–2010. Our results confirm that it is not possible to understand the current global terrestrial carbon sink without accounting for the sizeable sink due to forest demography. They also imply that a large portion of the current terrestrial carbon sink is strictly transient in nature.

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Sub-grid scale representation of vegetation in global land surface schemes: implications for estimation of the terrestrial carbon sink

Biogeosciences Discussions ◽

10.5194/bgd-10-16003-2013 ◽

2013 ◽

Vol 10 (10) ◽

pp. 16003-16041 ◽

Cited By ~ 1

Author(s):

J. R. Melton ◽

V. K. Arora

Keyword(s):

Water Balance ◽

Environmental Conditions ◽

Land Surface ◽

Carbon Balance ◽

Spatial Representation ◽

Carbon Sink ◽

Terrestrial Ecosystem ◽

Terrestrial Carbon ◽

Global Land ◽

Terrestrial Carbon Sink

Abstract. Terrestrial ecosystem models commonly represent vegetation in terms of plant functional types (PFTs) and use their vegetation attributes in calculations of the energy and water balance and to investigate the terrestrial carbon cycle. To accomplish these tasks, two approaches for PFT spatial representation are widely used: "composite" and "mosaic". The impact of these two approaches on the global carbon balance has been investigated with the Canadian Terrestrial Ecosystem Model (CTEM v 1.2) coupled to the Canadian Land Surface Scheme (CLASS v 3.6). In the composite (single-tile) approach, the vegetation attributes of different PFTs present in a grid cell are aggregated and used in calculations to determine the resulting physical environmental conditions (soil moisture, soil temperature, etc.) that are common to all PFTs. In the mosaic (multi-tile) approach, energy and water balance calculations are performed separately for each PFT tile and each tile's physical land surface environmental conditions evolve independently. Pre-industrial equilibrium CLASS-CTEM simulations yield global totals of vegetation biomass, net primary productivity, and soil carbon that compare reasonably well with observation-based estimates and differ by less than 5% between the mosaic and composite configurations. However, on a regional scale the two approaches can differ by > 30%, especially in areas with high heterogeneity in land cover. Simulations over the historical period (1959–2005) show different responses to evolving climate and carbon dioxide concentrations from the two approaches. The cumulative global terrestrial carbon sink estimated over the 1959–2005 period (excluding land use change (LUC) effects) differs by around 5% between the two approaches (96.3 and 101.3 Pg, for the mosaic and composite approaches, respectively) and compares well with the observation-based estimate of 82.2 ± 35 Pg C over the same period. Inclusion of LUC causes the estimates of the terrestrial C sink to differ by 15.2 Pg C (16%) with values of 95.1 and 79.9 Pg C for the mosaic and composite approaches, respectively. Spatial differences in simulated vegetation and soil carbon and the manner in which terrestrial carbon balance evolves in response to LUC, in the two approaches, yields a substantially different estimate of the global land carbon sink. These results demonstrate that the spatial representation of vegetation has an important impact on the model response to changing climate, atmospheric CO2 concentrations, and land cover.

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Global terrestrial carbon fluxes of 1999–2019 estimated by upscaling eddy covariance data with a random forest

Scientific Data ◽

10.1038/s41597-020-00653-5 ◽

2020 ◽

Vol 7 (1) ◽

Author(s):

Jiye Zeng ◽

Tsuneo Matsunaga ◽

Zheng-Hong Tan ◽

Nobuko Saigusa ◽

Tomoko Shirai ◽

...

Keyword(s):

Random Forest ◽

Ecosystem Respiration ◽

Gross Primary Production ◽

Net Ecosystem Exchange ◽

Carbon Fluxes ◽

Mitigation Policy ◽

Terrestrial Biosphere ◽

Area Index ◽

The World ◽

Global Land

Abstract The terrestrial biosphere is a key player in slowing the accumulation of carbon dioxide in the atmosphere. While quantification of carbon fluxes at global land scale is important for mitigation policy related to climate and carbon, measurements are only available at sites scarcely distributed in the world. This leads to using various methods to upscale site measurements to the whole terrestrial biosphere. This article reports a product obtained by using a Random Forest to upscale terrestrial net ecosystem exchange, gross primary production, and ecosystem respiration from FLUXNET 2015. Our product covers land from −60°S to 80°N with a spatial resolution of 0.1° × 0.1° every 10 days during the period 1999–2019. It was compared with four existing products. A distinguishable feature of our method is using three derived variables of leaf area index to represent plant functional type (PFT) so that measurements from different PFTs can be mixed better by the model. This product can be valuable for the carbon-cycle community to validate terrestrial biosphere models and cross check datasets.

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Global land carbon sink response to temperature and precipitation varies with ENSO phase

Environmental Research Letters ◽

10.1088/1748-9326/aa6e8e ◽

2017 ◽

Vol 12 (6) ◽

pp. 064007 ◽

Cited By ~ 22

Author(s):

Yuanyuan Fang ◽

Anna M Michalak ◽

Christopher R Schwalm ◽

Deborah N Huntzinger ◽

Joseph A Berry ◽

...

Keyword(s):

Carbon Sink ◽

Temperature And Precipitation ◽

Global Land ◽

Response To Temperature

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Strong time dependence of ocean acidification mitigation by atmospheric carbon dioxide removal

Nature Communications ◽

10.1038/s41467-019-13586-4 ◽

2019 ◽

Vol 10 (1) ◽

Cited By ~ 2

Author(s):

M. Hofmann ◽

S. Mathesius ◽

E. Kriegler ◽

D. P. van Vuuren ◽

H. J. Schellnhuber

Keyword(s):

Carbon Dioxide ◽

Global Warming ◽

Atmospheric Carbon Dioxide ◽

Carbon Sink ◽

Biogeochemical Cycles ◽

Mitigation Strategies ◽

Emissions Reduction ◽

Critical Difference ◽

Terrestrial Biosphere ◽

Favorable Conditions

AbstractIn Paris in 2015, the global community agreed to limit global warming to well below 2 $${}^{\circ }$$∘C, aiming at even 1.5 $${}^{\circ }$$∘C. It is still uncertain whether these targets are sufficient to preserve marine ecosystems and prevent a severe alteration of marine biogeochemical cycles. Here, we show that stringent mitigation strategies consistent with the 1.5 $${}^{\circ }$$∘C scenario could, indeed, provoke a critical difference for the ocean’s carbon cycle and calcium carbonate saturation states. Favorable conditions for calcifying organisms like tropical corals and polar pteropods, both of major importance for large ecosystems, can only be maintained if CO$${}_{2}$$2 emissions fall rapidly between 2025 and 2050, potentially requiring an early deployment of CO$${}_{2}$$2 removal techniques in addition to drastic emissions reduction. Furthermore, this outcome can only be achieved if the terrestrial biosphere remains a carbon sink during the entire 21st century.

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Controls of terrestrial ecosystem nitrogen loss on simulated productivity responses to elevated CO<sub>2</sub>

Biogeosciences ◽

10.5194/bg-15-5677-2018 ◽

2018 ◽

Vol 15 (18) ◽

pp. 5677-5698 ◽

Cited By ~ 6

Author(s):

Johannes Meyerholt ◽

Sönke Zaehle

Keyword(s):

Plant Growth ◽

Elevated Co2 ◽

Large Scale ◽

Nitrogen Availability ◽

Carbon Sink ◽

Nitrogen Loss ◽

Terrestrial Ecosystem ◽

Turnover Rates ◽

Terrestrial Biosphere ◽

Loss Rates

Abstract. The availability of nitrogen is one of the primary controls on plant growth. Terrestrial ecosystem nitrogen availability is not only determined by inputs from fixation, deposition, or weathering, but is also regulated by the rates with which nitrogen is lost through various pathways. Estimates of large-scale nitrogen loss rates have been associated with considerable uncertainty, as process rates and controlling factors of the different loss pathways have been difficult to characterize in the field. Therefore, the nitrogen loss representations in terrestrial biosphere models vary substantially, adding to nitrogen cycle-related uncertainty and resulting in varying predictions of how the biospheric carbon sink will evolve under future scenarios of elevated atmospheric CO2. Here, we test three commonly applied approaches to represent ecosystem-level nitrogen loss in a common carbon–nitrogen terrestrial biosphere model with respect to their impact on projections of the effect of elevated CO2. We find that despite differences in predicted responses of nitrogen loss rates to elevated CO2 and climate forcing, the variety of nitrogen loss representation between models only leads to small variety in carbon sink predictions. The nitrogen loss responses are particularly uncertain in the boreal and tropical regions, where plant growth is strongly nitrogen-limited or nitrogen turnover rates are usually high, respectively. This highlights the need for better representation of nitrogen loss fluxes through global measurements to inform models.

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Impact of changes in diffuse radiation on the global land carbon sink

Nature ◽

10.1038/nature07949 ◽

2009 ◽

Vol 458 (7241) ◽

pp. 1014-1017 ◽

Cited By ~ 575

Author(s):

Lina M. Mercado ◽

Nicolas Bellouin ◽

Stephen Sitch ◽

Olivier Boucher ◽

Chris Huntingford ◽

...

Keyword(s):

Carbon Sink ◽

Diffuse Radiation ◽

Global Land

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The climatic-induced net carbon sink by terrestrial biosphere over 1901–1995

Advances in Atmospheric Sciences ◽

10.1007/s00376-001-0033-1 ◽

2001 ◽

Vol 18 (6) ◽

pp. 1192-1206 ◽

Cited By ~ 2

Author(s):

Yang Xin ◽

Wang Mingxing ◽

Huang Yao

Keyword(s):

Carbon Sink ◽

Terrestrial Biosphere ◽

Net Carbon Sink

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Aerosol-light interactions reduce the carbon budget imbalance

Environmental Research Letters ◽

10.1088/1748-9326/ac3b77 ◽

2021 ◽

Author(s):

Michael O'Sullivan ◽

Yuan Zhang ◽

Nicolas Bellouin ◽

Ian Harris ◽

Lina M. Mercado ◽

...

Keyword(s):

Carbon Budget ◽

Carbon Sink ◽

Volcanic Eruptions ◽

Ground Level ◽

Diffuse Solar Radiation ◽

Global Carbon Budget ◽

Tropospheric Aerosol ◽

Separate Treatment ◽

Global Land ◽

Global Carbon

Abstract Current estimates of the global land carbon sink contain substantial uncertainties on interannual timescales which contribute to a non-closure in the global carbon budget in any given year. This budget imbalance (BIM) partly arises due to the use of imperfect models which are missing or misrepresenting processes. One such omission is the separate treatment of downward direct and diffuse solar radiation on photosynthesis. Here we evaluate and use an improved high-resolution (6-hourly), gridded dataset of surface solar diffuse and direct fluxes, over 1901-2017, constrained by satellite and ground-level observations, to drive two global land models. Results show that tropospheric aerosol-light interactions have the potential for substantial land carbon impacts (up to 0.4 PgCyr-1 enhanced sink) at decadal timescales, however large uncertainties remain, with models disagreeing on the direction of change in carbon uptake. On interannual timescales, results also show an enhancement of the land sink (up to 0.9 PgCyr-1) and subsequent reduction in BIM by 55% in years following volcanic eruptions. We therefore suggest global carbon budget assessments include this dataset in order to improve land sink estimates.

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Sub-grid scale representation of vegetation in global land surface schemes: implications for estimation of the terrestrial carbon sink

Biogeosciences ◽

10.5194/bg-11-1021-2014 ◽

2014 ◽

Vol 11 (4) ◽

pp. 1021-1036 ◽

Cited By ~ 33

Author(s):

J. R. Melton ◽

V. K. Arora

Keyword(s):

Land Cover ◽

Water Balance ◽

Environmental Conditions ◽

Land Surface ◽

Carbon Balance ◽

Carbon Sink ◽

Terrestrial Ecosystem ◽

Terrestrial Carbon ◽

Global Land ◽

Terrestrial Carbon Sink

Abstract. Terrestrial ecosystem models commonly represent vegetation in terms of plant functional types (PFTs) and use their vegetation attributes in calculations of the energy and water balance as well as to investigate the terrestrial carbon cycle. Sub-grid scale variability of PFTs in these models is represented using different approaches with the "composite" and "mosaic" approaches being the two end-members. The impact of these two approaches on the global carbon balance has been investigated with the Canadian Terrestrial Ecosystem Model (CTEM v 1.2) coupled to the Canadian Land Surface Scheme (CLASS v 3.6). In the composite (single-tile) approach, the vegetation attributes of different PFTs present in a grid cell are aggregated and used in calculations to determine the resulting physical environmental conditions (soil moisture, soil temperature, etc.) that are common to all PFTs. In the mosaic (multi-tile) approach, energy and water balance calculations are performed separately for each PFT tile and each tile's physical land surface environmental conditions evolve independently. Pre-industrial equilibrium CLASS-CTEM simulations yield global totals of vegetation biomass, net primary productivity, and soil carbon that compare reasonably well with observation-based estimates and differ by less than 5% between the mosaic and composite configurations. However, on a regional scale the two approaches can differ by > 30%, especially in areas with high heterogeneity in land cover. Simulations over the historical period (1959–2005) show different responses to evolving climate and carbon dioxide concentrations from the two approaches. The cumulative global terrestrial carbon sink estimated over the 1959–2005 period (excluding land use change (LUC) effects) differs by around 5% between the two approaches (96.3 and 101.3 Pg, for the mosaic and composite approaches, respectively) and compares well with the observation-based estimate of 82.2 ± 35 Pg C over the same period. Inclusion of LUC causes the estimates of the terrestrial C sink to differ by 15.2 Pg C (16%) with values of 95.1 and 79.9 Pg C for the mosaic and composite approaches, respectively. Spatial differences in simulated vegetation and soil carbon and the manner in which terrestrial carbon balance evolves in response to LUC, in the two approaches, yields a substantially different estimate of the global land carbon sink. These results demonstrate that the spatial representation of vegetation has an important impact on the model response to changing climate, atmospheric CO2 concentrations, and land cover.

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