Global trends in carbon sinks and their relationships with CO₂ and temperature

Elevated CO₂ concentrations increase photosynthesis and, potentially, net ecosystem production (NEP), meaning a greater CO₂ uptake. Climate, nutrients and ecosystem structure, however, influence the effect of increasing CO₂. Here we analysed global NEP from MACC-II and Jena CarboScope atmospheric inversions and ten dynamic global vegetation models (TRENDY), using statistical models to attribute the trends in NEP to its potential drivers: CO₂, climatic variables and land-use change. We found that an increased CO₂ was consistently associated with an increased NEP (1995–2014). Conversely, increased temperatures were negatively associated with NEP. Using the two atmospheric inversions and TRENDY, the estimated global sensitivities for CO₂ were 6.0 ± 0.1, 8.1 ± 0.3 and 3.1 ± 0.1 PgC per 100 ppm (~1 °C increase), and −0.5 ± 0.2, −0.9 ± 0.4 and −1.1 ± 0.1 PgC °C⁻¹ for temperature. These results indicate a positive CO₂ effect on terrestrial C sinks that is constrained by climate warming.