Lower Land Use Emissions Increased Net Land Carbon Sink During the Slow Warming Period

The terrestrial carbon sink has accelerated after 1998, concurrently with the slow warming period, but the mechanisms behind this acceleration are unclear. Here we analyse recent changes in the net land carbon sink and its driving factors using atmospheric inversions and terrestrial carbon models. We show that the linear trend of NLS during 1998-2012 is about 0.17±0.05 PgC yr^-2 - three times larger than during 1980-1998 (0.05±0.05 PgC yr^-2). According to terrestrial carbon model simulations, the intensification of the net land carbon sink cannot be explained by CO₂ fertilization or climate change alone. We therefore use a bookkeeping model to explore the contribution of changes in land-use emissions and find that decreasing land-use emissions are the dominant cause of the intensification of the land carbon sink during the slow warming period. This reduction of land-use emissions is due to both decreased tropical forest area loss and increased afforestation in northern temperate regions. The inversion-based estimate shows consistently reduced land-use emissions, while another bookkeeping model did not reproduce such change probably due to missing the signal of reduced tropical deforestation. These results highlight the importance of better constraining emissions from land-use change to understand recent trends in land carbon sinks.