Snow and ice lead to increased reflectance of incoming radiation. Beringia was unglaciated in the last glaciation. There was only one glaciation in the Northern Hemisphere during the Quaternary Period. The climate has become progressively warmer in the present interglacial. Isostatic uplift is the result of deposition of loess in periglacial regions.
Communities move intact in response to climate change.
Modern ecosystems do not provide modern analogues for all ecosystems in the recent past. Some pollen types are poorly preserved. Not all pollen types can be identified at the species level. The chronological sequence is often disturbed due to the mixing of material from different depths by physical processes. Some species produce large amounts of pollen, so they are over-represented in the diagram.