Vegetation-climate interactions in the warm mid-Cretaceous

Vegetation-climate interactions are thought to have amplified polar warmth during past warm periods. Here, we explore the vegetation-climate interactions in the mid-Cretaceous using a fully coupled ocean-atmosphere general circulation model with a dynamic vegetation component. We run simulations with 1x, 10x and 16x pre-industrial atmospheric CO ₂. Results show that forests expand from mid-latitudes to high latitudes as CO ₂ increases from 1x to 10x and 16x, mainly due to the CO ₂-induced warming. This expansion of mid-to-high latitude forests are largely supported by the distribution of mid-Cretaceous fossil woods and coal deposits. Globally, the presence of vegetation increases mean annual temperature and precipitation by 0.9 °C and 0.11 mm day ^-1 relative to bare ground. High-latitude warming induced by the presence of vegetation (∼1.9 °C) is less than half of that reported in previous studies. The weaker warming here is mainly due to less pronounced albedo feedbacks, and to a less extent, reduced poleward heat transport via weakening of the meridional overturning circulation. Our results suggest that other mechanisms in addition to high atmospheric CO ₂ and high-latitude vegetation are required to maintain the polar warmth.