Technical Note: Past and future warming – direct comparison on multi-century timescales

Abstract

In 2013, the Intergovernmental Panel on Climate Change concluded that Northern Hemisphere temperatures had reached levels unprecedented in at least 1400 years. The 2021 report now sees global mean temperatures rising to levels unprecedented in over 100 000 years. This Technical Note briefly explains the reasons behind this major change. Namely, the new assessment reflects additional global warming that occurred between the two reports and improved paleotemperature reconstructions that extend further back in time. In addition to past and recent warming, the conclusion also considers multi-century future warming, which thereby enables a direct comparison with paleotemperature reconstructions on multi-century time scales.