Issue Earth system models may overestimate land carbon resilience

Summary

Many mitigation scenarios and remaining carbon budget estimates assume that land carbon sinks keep working throughout the transition to net-zero emissions. Yet many Earth-system models represent vegetation with a few average plant types rather than locally adapted, diverse communities, treating it like simplified "big leaves" on grid cells tens to hundreds of kilometers wide. Modeled vegetation therefore responds smoothly to rising carbon dioxide and recovers easily after disturbance, missing how real trees die one by one through water stress, carbon starvation and pests. The danger is greatest when this combines with climate models that struggle to reproduce the size, duration and legacy of droughts and compound extremes. The report stresses that models remain indispensable, and its concern is specifically that they may overstate the resilience of the land sink. If that assumption is too optimistic, the real remaining carbon budget is smaller, warming and tipping risks during the transition are higher and reliance on carbon removal grows.