Abstract
Despite several decades of effort to constrain equilibrium climate
sensitivity (ECS), current best estimates still exhibit a large spread.
Past studies have sought to reduce ECS uncertainty through a variety of
methods including emergent constraints. One example uses global
temperature variability over the past century to constrain ECS. While
this method shows promise, it has been criticized for its susceptibility
to the influence of anthropogenic forcing and the limited length of the
instrumental record used to compute temperature variability. Here, we
investigate the emergent relationship between ECS and two metrics of
global temperature variability using model simulations and paleoclimate
reconstructions over the last millennium (850-1999). We find empirical
evidence in support of these emergent relationships. Observational
constraints suggest a central ECS estimate of 2.6-2.8K, consistent with
the Intergovernmental Panel on Climate Change’s consensus estimate of
3K. Moreover, they suggest “likely” ranges of ECS between 1.8-3.3K and
2.0-3.6K.