Legacy Effects from Historical Environmental Changes Dominate Future Terrestrial Carbon Uptake

The carbon balance of terrestrial ecosystems is determined by environmental drivers (chiefly related to climate and land use) which interact with each other and change over time. In particular, ecosystems are presently still affected by past environmental changes because they have not yet reached equilibrium with their environment. However, the magnitude and drivers of this legacy effect for the upcoming decades are still unclear. Here, we use the dynamic global vegetation model LPJ-GUESS to calculate the effects of historical (1850-2015) and future (2015-2099, exemplarily for the high emission/moderate deforestation scenario SSP5-8.5) environmental changes on historical and future terrestrial carbon cycling and to quantify the contributions of the following environmental drivers: climate change, CO2 fertilization, agricultural expansion, shifting cultivation frequency, wood harvest, nitrogen deposition, and nitrogen fertilization.According to our simulations, the land represented a cumulative net carbon source (-154 GtC) over the historical period mainly due to deforestation, wood harvest, and negative climate change impacts partly offset by carbon uptake via increased CO2 levels and nitrogen input. In contrast, the land is simulated to act as a net carbon sink (+118 GtC) over the 21st century. This is mostly a result of historical environmental changes as ecosystems still adapt to present-day CO2 and nitrogen availability as well as long-term vegetation regrowth following agricultural abandonment and wood harvest. The net impact of future environmental changes on future carbon cycling is much smaller because effects from individual environmental drivers largely compensate. Historical environmental changes dominate future terrestrial carbon cycling at least until mid-century when legacy effects gradually diminish and future environmental changes start to trigger carbon accumulation. Our results suggest that legacy effects persist even many decades after environmental changes occurred and need to be considered when interpreting alterations of the terrestrial carbon cycle.

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Nitrogen feedbacks increase future terrestrial ecosystem carbon uptake in an individual-based dynamic vegetation model

Biogeosciences Discussions ◽

10.5194/bgd-11-151-2014 ◽

2014 ◽

Vol 11 (1) ◽

pp. 151-185 ◽

Cited By ~ 7

Author(s):

D. Wårlind ◽

B. Smith ◽

T. Hickler ◽

A. Arneth

Keyword(s):

Carbon Sequestration ◽

Nitrogen Cycle ◽

Environmental Changes ◽

Nitrogen Dynamics ◽

Carbon Uptake ◽

Terrestrial Carbon ◽

Vegetation Model ◽

Carbon And Nitrogen ◽

Dynamic Vegetation Model ◽

Ecosystem Carbon

Abstract. Recently a considerable amount of effort has been put into quantifying how interactions of the carbon and nitrogen cycle affect future terrestrial carbon sinks. Dynamic vegetation models, representing the nitrogen cycle with varying degree of complexity, have shown diverging constraints of nitrogen dynamics on future carbon sequestration. In this study, we use the dynamic vegetation model LPJ-GUESS to evaluate how population dynamics and resource competition between plant functional types, combined with nitrogen dynamics, have influenced the terrestrial carbon storage in the past and to investigate how terrestrial carbon and nitrogen dynamics might change in the future (1850 to 2100; one exemplary "business-as-usual" climate scenario). Single factor model experiments of CO2 fertilisation and climate change show generally similar directions of the responses of C–N interactions, compared to the C-only version of the model, as documented in previous studies. Under a RCP 8.5 scenario, nitrogen limitation suppresses potential CO2 fertilisation, reducing the cumulative net ecosystem carbon uptake between 1850 and 2100 by 61%, and soil warming-induced increase in nitrogen mineralisation reduces terrestrial carbon loss by 31%. When environmental changes are considered conjointly, carbon sequestration is limited by nitrogen dynamics until present. However, during the 21st century nitrogen dynamics induce a net increase in carbon sequestration, resulting in an overall larger carbon uptake of 17% over the full period. This contradicts earlier model results that showed an 8 to 37% decrease in carbon uptake, questioning the often stated assumption that projections of future terrestrial C dynamics from C-only models are too optimistic.

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Effect of nitrogen deposition on China's terrestrial carbon uptake in the context of multifactor environmental changes

Ecological Applications ◽

10.1890/10-1685.1 ◽

2012 ◽

Vol 22 (1) ◽

pp. 53-75 ◽

Cited By ~ 77

Author(s):

Chaoqun Lu ◽

Hanqin Tian ◽

Mingliang Liu ◽

Wei Ren ◽

Xiaofeng Xu ◽

...

Keyword(s):

Nitrogen Deposition ◽

Environmental Changes ◽

Carbon Uptake ◽

Terrestrial Carbon

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Consequences of Considering Carbon–Nitrogen Interactions on the Feedbacks between Climate and the Terrestrial Carbon Cycle

Journal of Climate ◽

10.1175/2008jcli2038.1 ◽

2008 ◽

Vol 21 (15) ◽

pp. 3776-3796 ◽

Cited By ~ 246

Author(s):

Andrei P. Sokolov ◽

David W. Kicklighter ◽

Jerry M. Melillo ◽

Benjamin S. Felzer ◽

C. Adam Schlosser ◽

...

Keyword(s):

Carbon Sequestration ◽

Carbon Cycle ◽

Carbon Emissions ◽

Terrestrial Ecosystems ◽

Co2 Concentration ◽

Nitrogen Dynamics ◽

Carbon Uptake ◽

Terrestrial Carbon ◽

Surface Warming ◽

Terrestrial Carbon Cycle

Abstract The impact of carbon–nitrogen dynamics in terrestrial ecosystems on the interaction between the carbon cycle and climate is studied using an earth system model of intermediate complexity, the MIT Integrated Global Systems Model (IGSM). Numerical simulations were carried out with two versions of the IGSM’s Terrestrial Ecosystems Model, one with and one without carbon–nitrogen dynamics. Simulations show that consideration of carbon–nitrogen interactions not only limits the effect of CO2 fertilization but also changes the sign of the feedback between the climate and terrestrial carbon cycle. In the absence of carbon–nitrogen interactions, surface warming significantly reduces carbon sequestration in both vegetation and soil by increasing respiration and decomposition (a positive feedback). If plant carbon uptake, however, is assumed to be nitrogen limited, an increase in decomposition leads to an increase in nitrogen availability stimulating plant growth. The resulting increase in carbon uptake by vegetation exceeds carbon loss from the soil, leading to enhanced carbon sequestration (a negative feedback). Under very strong surface warming, however, terrestrial ecosystems become a carbon source whether or not carbon–nitrogen interactions are considered. Overall, for small or moderate increases in surface temperatures, consideration of carbon–nitrogen interactions result in a larger increase in atmospheric CO2 concentration in the simulations with prescribed carbon emissions. This suggests that models that ignore terrestrial carbon–nitrogen dynamics will underestimate reductions in carbon emissions required to achieve atmospheric CO2 stabilization at a given level. At the same time, compensation between climate-related changes in the terrestrial and oceanic carbon uptakes significantly reduces uncertainty in projected CO2 concentration.

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Effect of increasing CO2 on the terrestrial carbon cycle

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1407302112 ◽

2014 ◽

Vol 112 (2) ◽

pp. 436-441 ◽

Cited By ~ 244

Author(s):

David Schimel ◽

Britton B. Stephens ◽

Joshua B. Fisher

Keyword(s):

Climate Change ◽

Carbon Cycle ◽

Terrestrial Ecosystems ◽

Future Climate Change ◽

Carbon Uptake ◽

Model Diagnostics ◽

Terrestrial Carbon ◽

Terrestrial Carbon Cycle ◽

New Space ◽

Improved Model

Feedbacks from the terrestrial carbon cycle significantly affect future climate change. The CO2 concentration dependence of global terrestrial carbon storage is one of the largest and most uncertain feedbacks. Theory predicts the CO2 effect should have a tropical maximum, but a large terrestrial sink has been contradicted by analyses of atmospheric CO2 that do not show large tropical uptake. Our results, however, show significant tropical uptake and, combining tropical and extratropical fluxes, suggest that up to 60% of the present-day terrestrial sink is caused by increasing atmospheric CO2. This conclusion is consistent with a validated subset of atmospheric analyses, but uncertainty remains. Improved model diagnostics and new space-based observations can reduce the uncertainty of tropical and temperate zone carbon flux estimates. This analysis supports a significant feedback to future atmospheric CO2 concentrations from carbon uptake in terrestrial ecosystems caused by rising atmospheric CO2 concentrations. This feedback will have substantial tropical contributions, but the magnitude of future carbon uptake by tropical forests also depends on how they respond to climate change and requires their protection from deforestation.

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Changes in oceanic and terrestrial carbon uptake since 1982

Nature ◽

10.1038/373326a0 ◽

1995 ◽

Vol 373 (6512) ◽

pp. 326-330 ◽

Cited By ~ 366

Author(s):

R. J. Francey ◽

P. P. Tans ◽

C. E. Allison ◽

I. G. Enting ◽

J. W. C. White ◽

...

Keyword(s):

Carbon Uptake ◽

Terrestrial Carbon

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Nitrogen deposition: how important is it for global terrestrial carbon uptake?

Biogeosciences Discussions ◽

10.5194/bgd-10-11077-2013 ◽

2013 ◽

Vol 10 (7) ◽

pp. 11077-11109 ◽

Cited By ~ 1

Author(s):

G. Bala ◽

N. Devaraju ◽

R. K. Chaturvedi ◽

K. Caldeira ◽

R. Nemani

Keyword(s):

Nitrogen Deposition ◽

Carbon Storage ◽

Climate Warming ◽

N Deposition ◽

Carbon Uptake ◽

Terrestrial Carbon ◽

Co2 Fertilization ◽

Current Increase ◽

Community Land Model ◽

Global Mean

Abstract. Global carbon budget studies indicate that the terrestrial ecosystems have remained a~large sink for carbon despite widespread deforestation activities. CO2-fertilization, N deposition and re-growth of mid-latitude forests are believed to be key drivers for land carbon uptake. In this study, we assess the importance of N deposition by performing idealized near-equilibrium simulations using the Community Land Model 4.0 (CLM4). In our equilibrium simulations, only 12–17% of the deposited Nitrogen is assimilated into the ecosystem and the corresponding carbon uptake can be inferred from a C : N ratio of 20:1. We calculate the sensitivity of the terrestrial biosphere for CO2-fertilization, climate warming and N deposition as changes in total ecosystem carbon for unit changes in global mean atmospheric CO2 concentration, global mean temperature and Tera grams of Nitrogen deposition per year, respectively. Based on these sensitivities, it is estimated that about 242 PgC could have been taken up by land due to the CO2 fertilization effect and an additional 175 PgC taken up as a result of the increased N deposition since the pre-industrial period. Because of climate warming, terrestrial ecosystem could have lost about 152 PgC during the same period. Therefore, since preindustrial times terrestrial carbon losses due to warming may have been approximately compensated by effects of increased N deposition, whereas the effect of CO2-fertilization is approximately indicative of the current increase in terrestrial carbon stock. Our simulations also suggest that the sensitivity of carbon storage to increased N deposition decreases beyond current levels, indicating climate warming effects on carbon storage may overwhelm N deposition effects in the future.

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