UC Santa Cruz

Earth system feedbacks can amplify greenhouse gas forcing but are difficult to quantify, particularly on land where long palaeoclimate records are scarce. Here we reconstructed warm-season temperatures and vegetation at Lake Baikal, Russia, over the past 8.6 million years. We document gradual late Neogene cooling that was punctuated by an abrupt transition approximately 2.7 million years ago to severe cold temperatures during glacial periods. Forests were replaced by open steppe–tundra ecosystems and permafrost probably extended into South Siberia during these Early Pleistocene cold intervals. Compiled palaeobotanical data suggest this ecosystem turnover occurred throughout the Arctic and subarctic, although the timescale of these changes is less understood. Reconstructed Early Pleistocene glacial temperatures and vegetation resemble Late Pleistocene glacial periods at Lake Baikal, despite much warmer mean global temperatures in the Early Pleistocene. These geologic observations support the view that regional climate can respond nonlinearly to global forcing. We hypothesize that both vegetation albedo and permafrost carbon storage may have played a key role in amplifying glacial–interglacial climate cycles through the last 2.7 million years alongside ocean and ice sheet feedbacks.