Rapid vegetation changes of the late Quaternary

During glacial cycles of the late Quaternary, terrestrial vegetation changed globally in response to orbitally controlled insolation changes, variable levels of carbon dioxide, and availability of ice-free land. As they developed, the emerging vegetation patterns also in turn influenced climatic and carbon cycle trends via biogeophysical and biogeochemical feedbacks. Although such trends are clearly seen in proxy data covering glacial cycles, the vegetation patterns still remain poorly constrained due to short, scarce and discontinuous plant fossil and pollen records. For understanding the varying vegetation patterns, and for assessing terrestrial sources and causes of rapid atmospheric greenhouse gas changes, we have simulated the entire last glacial cycle, covering over 130,000 years, using an Earth system model with dynamic vegetation, carbon pools and methane emissions. In line with proxy records, our simulation shows an Eemian interglacial globally warmer than the preindustrial era, with slightly more boreal forest cover and a greener Sahara, while the simulated much colder Last Glacial Maximum, has larger subtropical deserts, more boreal tundra and fragmented tropical forests. We separate regions where vegetation change is mainly bound to forcing from ice-sheet extent (and sea level) or carbon dioxide fertilization, or the result of a feedback response to climate change. Regions where the feedbacks with climate are strong, like in northern Africa where there is hydroclimate-driven vegetation growth, and eastern Siberia where there is thermally-driven taiga-tundra turnover, the vegetation responses are highly dynamic, including a clear precessional signal that propagates to land carbon allocation and greenhouse gas emissions. Such regions have the largest potential to contribute to rapid changes in atmospheric greenhouse gases, besides any fast changes that depend directly on cryosphere or sea-level dynamics. In contrast, large parts of the tropics have vegetation with a muted response to climate change, and rapid coverage changes within this region may only occur when there are sudden changes in carbon dioxide fertilization.