Observations of Climate Feedbacks over 2000–10 and Comparisons to Climate Models

Abstract

eedbacks in response to climate variations during the period 2000?10 have been calculated using reanalysis meteorological fields and top-of-atmosphere flux measurements. Over this period, the climate was stabilized by a strongly negative temperature feedback (~?3 W m?2 K?1); climate variations were also amplified by a strong positive water vapor feedback (~+1.2 W m?2 K?1) and smaller positive albedo and cloud feedbacks (~+0.3 and +0.5 W m?2 K?1, respectively). These observations are compared to two climate model ensembles, one dominated by internal variability (the control ensemble) and the other dominated by long-term global warming (the A1B ensemble). The control ensemble produces global average feedbacks that agree within uncertainties with the observations, as well as producing similar spatial patterns. The most significant discrepancy was in the spatial pattern for the total (shortwave + longwave) cloud feedback. Feedbacks calculated from the A1B ensemble show a stronger negative temperature feedback (due to a stronger lapse-rate feedback), but that is cancelled by a stronger positive water vapor feedback. The feedbacks in the A1B ensemble tend to be more smoothly distributed in space, which is consistent with the differences between El Niño?Southern Oscillation (ENSO) climate variations and long-term global warming. The sum of all of the feedbacks, sometimes referred to as the thermal damping rate, is ?1.15 ± 0.88 W m?2 K?1 in the observations and ?0.60 ± 0.37 W m?2 K?1 in the control ensemble. Within the control ensemble, models that more accurately simulate ENSO tend to produce thermal damping rates closer to the observations. The A1B ensemble average thermal damping rate is ?1.26 ± 0.45 W m?2 K?1.