CMIP6中陆地-植被系统的状态转变在巴黎协定规定的变暖水平下出现
State transitions in land-vegetation systems emerge at Paris Agreement warming levels in CMIP6
AI总结：
本研究基于CMIP6集合识别陆地-植被系统的9类共47种状态转变，发现巴黎协定规定的2℃或更低变暖已足以触发多数转变，揭示了不同区域转变的驱动机制。
AI中文摘要：
本研究将自动检测工作流程应用于未来排放情景下的第六阶段耦合模式比较计划（CMIP6）集合，识别出地球系统陆地-植被分量中47种突发及更渐进发展的状态转变，分为9个类别。在亚马逊地区，发现植被枯萎与绿化两种状态转变案例，二者的差异主要源于降水不同：出现枯萎的模式要么降水绝对降幅更大，要么降水更易转化为土壤水分流失，尤其是近地表；而在绿化模式中，若土壤水分流失较弱，CO₂肥效则占优。易发生枯萎的模式中，降水减少似乎由湿对流减弱驱动。在亚马逊所有案例中，动态植被模式会出现枯萎，而绿化仅见于植被分布固定的模式。非洲案例包括非洲中东部与刚果盆地的绿化，以及刚果地区突发的土壤水分干燥。高纬度地区，北方森林扩张，且当区域零上温度持续超过半年时，永久冻土融化。其他类别包括北美东北部积雪覆盖减少的转变、青藏高原及东南亚附近植被生物量增加，以及北美东北部叶面积指数增加。特别值得关注的是，巴黎协定目标范围内可实现的2℃或更低的全球变暖，已足以触发CMIP6中多数已识别类别的转变。
英文摘要：
Using an automatic detection workflow applied to the Coupled Model Intercomparison Project Phase 6 (CMIP6) ensemble under future emission scenarios, we identify 47 abrupt and more gradually developing state transitions in the land-vegetation component of the Earth system, classified into 9 categories. Over the Amazon, we find state transitions via vegetation dieback alongside greening cases; the contrast between them is traced primarily to differences in precipitation: models showing dieback experience either a larger absolute decline in precipitation, or one that translates more efficiently into soil moisture loss, particularly near the surface, while in greening models the CO$_2$ fertilization effect wins out where the soil moisture loss remains weaker. The precipitation decline in dieback-prone models appears driven through a weakening of moist convection. Across these Amazon cases, models with dynamic vegetation undergo dieback, whereas greening is confined to models with prescribed vegetation distributions. African cases include greening over eastern-central Africa and the Congo basin, and an abrupt soil-moisture drying also over the Congo. At high latitudes, boreal forest expands, while permafrost thaws once the regional above-zero temperatures persist for more than half the year. Additional categories cover transitions to a reduced snow-cover state over northeastern North America, increased vegetation biomass near the Tibetan Plateau and southeastern Asia, and increased leaf-area index over the northeast Northern America. Of particular concern, a global warming of 2$^\circ$C or below, within reach of the Paris Agreement targets, is already enough to trigger the onset of the majority of the identified categories in CMIP6.
