Paleoclimate Perspectives on Contemporary Climate Change

Paleoclimate data have informed contemporary climate science, and could do so more extensively. Quaternary data record glacial–interglacial cycles paced by variations in Earth’s orbit. Faster climate changes include repeated warming–cooling (Dansgaard–Oeschger) cycles during glacial times as well as abrupt glacial terminations, suggesting repeated crossings of a tipping point. Climate models reproduce some key features of past climate change but not others, including patterns of orbitally forced precipitation changes and linkages between different modes of climate variability. Land ecosystem records document plant species’ resilience to rapid climate change, in contrast to large mammals’ vulnerability; multiple roles of natural wildfires; and effects of low glacial CO2 on vegetation and fire. Dansgaard– Oeschger cycles constrain biogeochemical feedbacks, showing large increases of CH4 and N2O with warming and suggesting destabilizing feedbacks through land surface albedo under glacial conditions. Lessons for conservation include recognizing “novel” ecosystems as normal and respecting the paramount role of species movements as responses to rapid climate change.