Open AccessA review of the major drivers of the terrestrial carbon uptake: model-based assessments, consensus, and uncertainties
Author(s) -
Thejna Tharammal,
Govindasamy Bala,
N. Devaraju,
Ramakrishna R. Nemani
Publication year - 2019
Publication title -
environmental research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.37
H-Index - 124
ISSN - 1748-9326
DOI - 10.1088/1748-9326/ab3012
Subject(s) - environmental science , carbon sink , climate change , greenhouse gas , coupled model intercomparison project , land use, land use change and forestry , carbon cycle , global change , land use , carbon sequestration , carbon fibers , deposition (geology) , global warming , soil carbon , sink (geography) , atmospheric sciences , nitrogen , climate model , ecology , ecosystem , soil water , soil science , geography , chemistry , computer science , geology , algorithm , composite number , biology , paleontology , cartography , organic chemistry , sediment
Terrestrial and oceanic carbon sinks together sequester >50% of the anthropogenic emissions, and the major uncertainty in the global carbon budget is related to the terrestrial carbon cycle. Hence, it is important to understand the major drivers of the land carbon uptake to make informed decisions on climate change mitigation policies. In this paper, we assess the major drivers of the land carbon uptake—CO 2 fertilization, nitrogen deposition, climate change, and land use/land cover changes (LULCC)—from existing literature for the historical period and future scenarios, focusing on the results from fifth Coupled Models Intercomparison Project (CMIP5). The existing literature shows that the LULCC fluxes have led to a decline in the terrestrial carbon stocks during the historical period, despite positive contributions from CO 2 fertilization and nitrogen deposition. However, several studies find increases in the land carbon sink in recent decades and suggest that CO 2 fertilization is the primary driver (up to 85%) of this increase followed by nitrogen deposition (∼10%–20%). For the 21st century, terrestrial carbon stocks are projected to increase in the majority of CMIP5 simulations under the representative concentration pathway 2.6 (RCP2.6), RCP4.5, and RCP8.5 scenarios, mainly due to CO 2 fertilization. These projections indicate that the effects of nitrogen deposition in future scenarios are small (∼2%–10%), and climate warming would lead to a loss of land carbon. The vast majority of the studies consider the effects of only one or two of the drivers, impairing comprehensive assessments of the relative contributions of the drivers. Further, the broad range in magnitudes and scenario/model dependence of the sensitivity factors pose challenges in unambiguous projections of land carbon uptake. Improved representation of processes such as LULCC, fires, nutrient limitation and permafrost thawing in the models are necessary to constrain the present-day carbon cycle and for more accurate future projections.