Vegetation Pattern and Terrestrial Carbon Variation in Past Warm and Cold Climates.

Understanding the transition of biosphere‐atmosphere carbon exchange between glacial and interglacial climates can constrain uncertainties in its future projections. Using an individual‐based dynamic vegetation model, we simulate vegetation distribution and terrestrial carbon cycling in past cold and warm climates and elucidate the forcing effects of temperature, precipitation, atmospheric CO2 concentration (pCO2), and landmass. Results are consistent with proxy reconstructions and reveal that the vegetation extent is mainly determined by temperature anomalies, especially in a cold climate, while precipitation forcing effects on global‐scale vegetation patterns are marginal. The pCO2 change controls the global carbon balance with the fertilization effect of higher pCO2 linking to higher vegetation coverage, an enhanced terrestrial carbon sink, and increased terrestrial carbon storage. Our results indicate carbon transfer from ocean and permafrost/peat to the biosphere and atmosphere and highlight the importance of forest expansion as a driver of terrestrial ecosystem carbon stock from cold to warm climates. Plain Language Summary: The terrestrial biosphere plays a key role in mitigating climate change by sequestering the anthropogenic carbon emissions in the atmosphere. The projected change in biosphere‐atmosphere carbon exchange remains highly uncertain due to competing effects of elevated CO2 concentration and the accompanying climate forcing. Studying how the carbon balance changed in the past cold and warm climate transitions can help to constrain these uncertainties. Here we perform dynamic vegetation model simulations to reproduce the vegetation patterns and terrestrial carbon variations in these climate states, which are consistent with paleo‐vegetation and carbon cycle‐related reconstructions. We further investigate separately the climate forcing effects (precipitation, temperature, and CO2 concentration) and take into account the different land‐sea distributions. We conclude that global vegetation distribution is mainly determined by temperature anomalies rather than precipitation anomalies. Furthermore, the forest expansion from the cold to warm climate state, mainly driven by CO2 fertilization effect, contributes the most to an increased terrestrial ecosystem carbon stock. Key Points: Vegetation pattern and terrestrial carbon cycling in past cold and warm climates are simulated consistently by a dynamic vegetation modelThe glacial‐interglacial temperature changes have larger influences on the global vegetation extent than precipitation anomaliesThe CO2 concentration, by affecting forest coverage through the fertilization effect, dominates the changes of terrestrial carbon stock [ABSTRACT FROM AUTHOR]