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. We examine the relationships in models andreconstructions between the multidecadal variability of surface temperaturein East Asia and two extratropical modes of variability: the AtlanticMultidecadal Oscillation (AMO) and the Pacific Decadal Oscillation (PDO). Weanalyse the spatial, temporal and spectral characteristics of the climatemodes in the last millennium, historical and pre-industrial control simulationsof seven Coupled Model IntercomparisonProject phase 5 (CMIP5)/Paleoclimate ModelIntercomparison Project phase 3 (PMIP3) global climate models (GCMs) to assess the relative influences of externalforcing and unforced variability. These models produce PDO and AMOvariability with realistic spatial patterns but widely varying spectralcharacteristics. AMO internal variability significantly influences EastAsian temperature in five models (MPI, HadCM3, MRI, IPSL and CSIRO) but has aweak influence in the other two (BCC and CCSM4). In most models, externalforcing greatly strengthens these statistical associations and hence theapparent teleconnection with the AMO. PDO internal variability stronglyinfluences East Asian temperature in two out of seven models, but externalforcing makes this apparent teleconnection much weaker. This indicates thatthe AMO–East Asian temperature relationship is partly driven by externalforcing, whereas the PDO–temperature relationship is largely from internalvariability within the climate system. Our findings suggest that externalforcing confounds attempts to diagnose the teleconnections of internalmultidecadal variability. Using AMO and PDO indices that represent internalvariability more closely and minimising the influence of external forcing onEast Asian temperature can partly ameliorate this confounding effect.Nevertheless, these approaches still yield differences between the forcedand control simulations and they cannot always be applied to paleoclimatereconstructions. Thus, we recommend caution when interpreting teleconnectionsdiagnosed from reconstructions that contain both forced and internalvariations.

Identifying teleconnections and multidecadal variability of East Asian surface temperature during the last millennium in CMIP5 simulations