Four colours of carbon sinks in terrestrial ecosystems

<p>Terrestrial ecosystems are important carbon (C) sinks that absorb 31% of anthropogenic carbon dioxide (CO<sub>2</sub>) emissions. Understanding the formation mechanisms and enhancement strategies of terrestrial carbon sinks is necessary for assessing their magnitude, spatiotemporal dynamics, and potential. This knowledge is also the foundation for implementing effective management measures and technological approaches to enhance terrestrial carbon sinks, which is essential for achieving carbon neutrality and limiting global warming to less than 1.5°C. Here we propose that the terrestrial carbon sinks can be systematically conceptualized into four colours, specifically green carbon, black carbon, blue carbon, and white carbon. We elucidate the definition, current distribution, and approaches for enhancing carbon sinks of these four colours. Our results indicate that the current four-colour carbon sink globally is 4.4 Pg C yr<sup>-1</sup>. The global potential to enhance the four-colour carbon sinks is estimated to be 11.9 ± 2.2 Pg C yr<sup>-1</sup>. Using China as a case study, where its current four-colour carbon sink amounts to 0.74 Pg C yr<sup>-1</sup>, we also introduce the approaches to enhancing carbon sinks of these colours, along with their mitigation potential, costs, environmental risks, and social acceptance. Finally, we highlight priority research areas for future studies to advance the scientific and practical understanding of terrestrial carbon sinks.</p>