Natural and Anthropogenic Climate Variability Signals in a 237‐Year‐Long Coral Record From the Philippines

Both proxy and model studies conducted to understand anthropogenic warming have revealed historical variations in sea‐surface temperature (SST) since the industrial revolution. However, because of discrepancies between observations and models in the late nineteenth century, the timing and degree of anthropogenic warming remain unclear. In this study, we reconstructed a 237‐year‐long record of SST and salinity using a coral core collected from Bicol, southern Luzon, Philippines, which is located at the northern edge of the western Pacific warm pool. The SST record showed volcanic cooling after several volcanic eruptions, including the 1815 Tambora eruption, but the pattern of change differed. Decadal SST variations at Bicol are connected to Pacific Decadal Variability (PDV). Therefore, it is suggested that the PDV conditions at the time of the eruption may have influenced marine conditions, such as the degree and duration of cooling and/or salinity, after the eruptions. Although there were discrepancies in SST variations among the modeled, observed, and proxy SST data from the late nineteenth to early twentieth centuries, SST data from the late twentieth century showed globally coherent anthropogenic warming, especially after 1976. In particular, summer SST in the northwestern Pacific has become more sensitive to anthropogenic forcing since 1976. Global warming is a growing concern worldwide, and model studies play an important role in predicting climate change. To improve the accuracy of the model, a comparison with observed data is critical. However, continuous observed data are spatially inadequate, and sometimes there is a discrepancy between the model and observed data. Therefore, proxy data, such as coral skeletons, were used to understand climate variability. In this study, we measured geochemical tracers in a coral skeleton collected from Bicol, southern Luzon, Philippines, and reconstructed the sea surface temperature (SST) and salinity data for more than 200 years. The SST record shows several cooling events due to volcanic eruptions, such as the Tambora eruptions in 1815. Overall SST variations at Bicol are likely to be connected to Pacific Decadal Variability. The SST profile in the modeled, observed, and proxy data from the late nineteenth to early twentieth centuries showed discrepancies. However, the anthropogenic warming indicated by the SST data of the late twentieth century was globally coherent, especially after 1976. Coral geochemical data from the Philippines show volcanic cooling only during the nineteenth centuryThe decadal variation in sea‐surface temperature in this study showed a close relationship with the Pacific decadal variabilityThe warming trend observed in the late twentieth century suggests that recent warming was globally synchronous Coral geochemical data from the Philippines show volcanic cooling only during the nineteenth century The decadal variation in sea‐surface temperature in this study showed a close relationship with the Pacific decadal variability The warming trend observed in the late twentieth century suggests that recent warming was globally synchronous