Potential strong contribution of future anthropogenic land-use and land-cover change to the terrestrial carbon cycle

Benjamin Quesada,Eddy Robertson,Nathalie De Noblet-Ducoudré,Almut Arneth

doi:10.1088/1748-9326/aac4c3

Abstract

Anthropogenic land-use and land cover changes (LULCC) affect global climate and global terrestrial carbon (C) cycle. However, relatively few studies have quantified the impacts of future LULCC on terrestrial carbon cycle. Here, using Earth system model simulations performed with and without future LULCC, under the RCP8.5 scenario, we find that in response to future LULCC, the carbon cycle is substantially weakened: browning, lower ecosystem C stocks, higher C loss by disturbances and higher C turnover rates are simulated. Projected global greening and land C storage are dampened, in all models, by 22% and 24% on average and projected C loss by disturbances enhanced by ~49% when LULCC are taken into account. By contrast, global net primary productivity is found to be only slightly affected by LULCC (robust +4% relative enhancement compared to all forcings, on average). LULCC is projected to be a predominant driver of future C changes in regions like South America and the southern part of Africa. LULCC even cause some regional reversals of projected increased C sinks and greening, particularly at the edges of the Amazon and African rainforests. Finally, in most carbon cycle responses, direct removal of C dominates over the indirect CO2 fertilization due to LULCC. In consequence, projections of land C sequestration potential and Earth’s greening could be substantially overestimated just because of not fully accounting for LULCC.

Highlights

Terrestrial soils and vegetation contribute to the global carbon cycle and climate mainly through biogeochemical emissions and uptake of greenhouse gases (CO2, CH4, N2O, etc) and exchange of energy, water and momentum [1–3]
The contributions of future land-use and land cover changes (LULCC) to the projections of global and regional terrestrial carbon cycle (2071– 2100) are assessed in a multi-model framework of five different Earth system model (ESM) and under a common realistic LULCC scenario (RCP8.5), distinguishing the direct impacts of carbon removal and the indirect CO2 emissions induced by those LULCC
If land carbon uptake is projected to increase under future greenhouse gases scenarios, mainly driven by the positive effects of CO2 fertilization of photosynthesis [5, 42], large uncertainties [9, 33, 54, 55], our results show that the ability of the terrestrial biosphere to sequester carbon from the atmosphere is substantially dampened by future LULCC

Summary

Introduction

Terrestrial soils and vegetation contribute to the global carbon cycle and climate mainly through biogeochemical emissions and uptake of greenhouse gases (CO2, CH4, N2O, etc) and exchange of energy, water and momentum (i.e. biophysical effects) [1–3]. The productivity and carbon stocks of terrestrial ecosystems can be in turn affected by climate and human use. Changes in terrestrial carbon storage are found to be positively correlated with changes in atmospheric CO2 concentration and negatively to temperature changes (∼1 PgC.ppm−1 and ∼−80 PgC.K−1 as approximated sensitivities among the studies [4–7]). Land-use and land cover changes (LULCC), like conversion of forests into crops or pastures, affect ecosystem-climate-carbon cycle processes through changes in biophysical properties of the land-cover, changes in phenology and changes in biogeochemical emissions and uptake. Over the last 150 years, estimated cumulative LULCC emissions represent approximately one-third of total cumulative anthropogenic CO2 emissions but only one-eighth over the recent period 1990–2010 [8, 10]

Objectives

Methods

Results

Conclusion