Radiative Forcing and Global Temperatures: 800,000 Years of Co-Movement

This paper evaluates paleoclimate sensitivity over the past 800,000 years using two recently proposed co-movement measures: Long-run covariability and quantile coherency. The former allows one to calculate long-run correlation as well as long-run regression coefficients. The latter is based on cross-spectral densities; it characterizes the dependence in quantiles of the joint distribution across frequencies. Both allow one to focus on long-term components of the data; this addresses the uncertainty associated with paleoclimatic reconstructions of radiative forcings as well as temperatures. The long-run correlation coefficient and long-run regression coefficient are found to be 0.87 and 0.76, respectively. The quantile coherency analysis finds that the dependence is generally stronger for the long-term components of the data, but also significantly lower in smaller quantiles of the joint distribution of temperatures and forcing. Thus, the relationship is weaker during full glacial climates compared to interglacial periods and intermediate glacial climates.