Time-variations of the climate feedback parameter λ are associated with the Pacific Decadal Oscillation

Climate models suggest that the climate feedback parameter λ , which denotes the magnitude of the Earth radiative response to a change in global surface temperature, varies with time. This is because λ depends on the pattern of sea-surface temperature. However, the time-variability of λ and its relation to the sea-surface temperature pattern has not been evaluated in multi-decadal observations. Here, using up-to-date observations, we evaluate the global energy budget over successive 25-year windows and derive a time-series of λ over 1970–2005. We find λ varied within the range [−3.2, −1.0]W ⋅ m −2 ⋅ K −1 since 1970. These variations are linked to the sea-surface temperature pattern changes associated with the Pacific Decadal Oscillation. Climate model simulations forced with observations of historical sea-surface temperature show a 1970–2005 mean λ that is consistent with observations. However, they fail in reproducing observed λ time-variations since 1970 which are associated to the Pacific Decadal Oscillation, meaning that climate models underestimate the pattern effect at decadal time scales.