Quantifying and understanding natural climate variability at the centennial time scale is critical for detecting and attributing externally forced changes. The era of modern instrumental records of key climate variables such as sea surface temperature (SST) and sea level pressure (SLP) began less than 200 years ago, requiring that this variability be characterized with paleoclimatic evidence or multi-century simulations from general circulation models (GCMs). Initial results from a 3,000-year integration of one state-of-the-art GCM suggests the dominant mode of centennial-scale (~100-500 year) natural climate variability in the tropics elicits synchronous changes in the mean annual temperature of the ocean surface at several geographic locations, including the South China Sea. The ability of the climate modeling community to corroborate this finding is severely hampered by a lack of observational data. Our project aims to construct a much-needed tropical SST record on multi-century time scales, and use that new proxy record to guide and ground-truth the detailed analysis of a set of four global coupled GCM simulations. To this end, we propose an interdisciplinary effort consisting of two parts: a complete diagnostic analysis of global coupled GCM output, focusing on low frequency (decadal to centennial scale) variability; and production of a new coral-based proxy record of annual SST spanning the last ~420 years. Although coral proxy records can be generated at much higher resolution (e.g., biweekly), the preliminary low-resolution (annual) coral record proposed here will allow us to confirm the presence of low frequency climate variability seen in the model(s) at relatively low cost, and lay the groundwork for future investigations at seasonal time scales. Quantifying and understanding centennial-scale climate variability is critical for detection and attribution of trends that may be emerging due to anthropogenic forcing. The proposed study will contribute substantially to the growing interest in low-frequency tropical climate variability, and place the PIs in position to help lead the charge into this rapidly emerging and relevant topic.
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