Scientific land greening under climate change: Theory, modeling, and challenges

Anthropogenic land greening is a vital strategy to combat the global warming crisis. However, the changing external environment and endowment factors may constrain the effectiveness of land greening. It remains unclear how to quantify and optimize land greening strategies scientifically. This article reviewed the theoretical foundations of land greening, pointing out that climate governance and human settlement quality improvement have gradually become the two core objectives of land greening since the 20th century. Multi-source and multi-scale experimental and observational surveys are important techniques for detecting and evaluating long-term land greening in the context of climate change, especially by forming experimental and observational networks. The theoretical mechanisms of interactions among climate, humans, and vegetation were also explored. For modeling approaches, hybrid modeling based on Earth system coupling theory may be the most promising but challenging approach. Four main challenges of scientific land greening were also discussed, including knowledge gaps related to land greening mechanisms, unclear multifaceted effects of land greening, lack of forward-looking quantitative assessment, and difficulties in evaluating synergies and trade-offs among assessment targets. Based on these, a strategic framework was proposed, including systematic observation, mechanism research, expectation assessment, and scientific planning for scientific greening programs in the Guangdong- Hong Kong- Macao Greater Bay Area. This review underscored the importance of proactively implementing land greening programs and provided guidelines for scientific greening based on cutting-edge theory and methods.