Reconstructions, Reconstructions Everywhere: A humble call for a Climate Reconstruction Intercomparison Project

The number of seasonal or annual climate reconstructions targeting the last 1000-2000 years has increased significantly over the last decade, particularly climate field reconstructions (CFRs) that provide spatially explicit estimates of multiple climate state variables such as surface temperature, precipitation, or sea level pressure.  This proliferation of CFRs has been driven by multiple factors, including increasing numbers of available proxies and methodological advances.  These developments have created a moment of opportunity, long in the making, in which seasonal and annual CFRs that target the last several millennia can better inform climate dynamics, model assessments, historical conditions, and characterizations of climate risks.  But how accurate are these CFRs, how well do they agree with each other, and how dependent are they on different methodological and data choices?  The importance of these questions will be demonstrated by comparing estimates of climate responses to large tropical eruptions derived from a state-of-the-science CFR ensemble.  The results of these comparisons subsequently will be used to propose a framework for developing a climate reconstruction intercomparison project to evaluate methodological choices, data dependencies, and reconstruction agreement.  This framework will include an exploration of systematic reconstruction and data protocols, as well as skill and comparison diagnostics.