CR 57:11-18 (2013)  -  DOI: https://doi.org/10.3354/cr01159

ABSTRACT: We examine the characteristics (amplitude and phase) of the temporal variation in the rates of global-mean surface temperature change during the past millennium. The study was conducted by applying 20, 30, and 50 yr sliding windows to the observations of the recent century and reconstructions of earlier times. The analysis focuses on the characteristics of the rate of warming during the 20th century within the context of the past millennium as well as its sensitivity to the low-frequency variability of sea surface temperature (SST) and the time scales. On the 20 yr time scale, rates comparable to that of the 20th century in both amplitude and phase occur in the preceding 9 centuries. The maximum in the amplitude of rates of temperature change in the 20th century on the 30 yr time scale, although not the largest during the past millennium, is the longest lasting. On the 50 yr time scale, the 20th century warming rates are the highest and the most persistent of the past millennium. The results also indicate that although the SST variability does not greatly affect the amplitude of the rates, the phases are quite different, highlighting the importance of the role of oceans in affecting the rates. We also analyze the characteristics of temperature change rates using global climate model (1000 to 1999 AD) simulations with different climate forcing (solar, volcanic, and greenhouse gases). Except for the case driven by solar forcing alone, all produce amplitudes similar to observed ones. However, only greenhouse gas forcing can reproduce the persistent high warming rates of the 20th century.

KEY WORDS: Rates of temperature change · Observation · Reconstruction · Model simulation · 20th century warming · The past millennium