IPCC Paleoclimate Streamlining: An alternative Perspective on Common Era Temperature Variability
The assessment of pre-instrumental climate variability during the Common Era (CE) has been a key element of IPCC reports and was recently emphasized by showing a single temperature reconstruction as the first figure in the 2021 Summary for Policymakers (SPM). This reconstruction is derived from dozens of proxy records including tree-rings, corals, ice cores and sediments, and displays the course of global temperatures over the past 2000 years. Show casing a single study for paleoclimate contextual evidence of recent warming in the SPM is not unprecedented. This was already done in 2001, when the now iconic Hockey Stick reconstruction was the main teaser of this important document. In 2001, however, all other reconstructions that were state-of-the-art at the time were also included in the full IPCC report. This is now different as none of the various recently published reconstructions is illustrated in the latest report that in its current form extends over some 3500 pages. Streamlining the 2021 SPM and report to only one reconstruction affects the conclusions that can be drawn from state-of-the-art paleoclimate research. We here show all recently published CE temperature reconstructions, discuss differences in reconstructed temperature variance and trends, and conclude that the reduced reconstructed variability highlighted in the 2021 SPM for the first millennium might substantially change when more high-resolution proxy series covering the entire CE become available.