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The tropical Pacific influences climate patterns across the globe, yet robust constraints on decadal to centennial‐scale climate variations are difficult to extract from sparse instrumental observations in this region. Oxygen isotope (δ¹⁸O) records from long‐lived corals enable the quantitative reconstruction of tropical Pacific climate variability and trends over the twentieth century and beyond, but such corals are exceedingly rare. Here, we use multiple short coral δ¹⁸O records to create a coral ‘ensemble’ reconstruction of twentieth century climate in the central tropical Pacific. Ten U/Th‐dated fossil coral δ¹⁸O records from Kiritimati Island (2°N, 157°W) span 1891 CE to 2006 CE, with the younger samples enabling quantitative comparison to a large ensemble of modern coral records and instrumental sea surface temperature. A composite record constructed of modern and fossil Kiritimati coral δ¹⁸O records shows a shift toward warmer and fresher conditions from 1970 CE onward, consistent with previously published records in this region.

Coral oxygen isotopes (δ¹⁸O) from the central equatorial Pacific provide monthly resolved records of El Niño‐Southern Oscillation activity over past centuries to millennia. However, calibration studies usingin situdata to assess the relative contributions of warming and freshening to coral δ¹⁸O records are exceedingly rare. Furthermore, the fidelity of coral δ¹⁸O records under the most severe thermal stress events is difficult to assess. Here, we present six coral δ¹⁸O records andin situtemperature, salinity, and seawater δ¹⁸O data from Kiritimati Island (2°N, 157°W) spanning the very strong 2015/16 El Niño event. Local sea surface temperature (SST) anomalies of +2.4 ± 0.4°C and seawater δ¹⁸O anomalies of −0.19 ± 0.02‰ contribute to the observed coral δ¹⁸O anomalies of −0.58 ± 0.05‰, consistent with a ∼70% contribution from SST and ∼30% from seawater δ¹⁸O. Our results demonstrate that Kiritimati coral δ¹⁸O records can provide reliable reconstructions even during the largest class of El Niño events.

The El Niño–Southern Oscillation (ENSO) represents the largest source of year‐to‐year global climate variability. While Earth system models suggest a range of possible shifts in ENSO properties under continued greenhouse gas forcing, many centuries of preindustrial climate data are required to detect a potential shift in the properties of recent ENSO extremes. Here we reconstruct the strength of ENSO variations over the last 7,000 years with a new ensemble of fossil coral oxygen isotope records from the Line Islands, located in the central equatorial Pacific. The corals document a significant decrease in ENSO variance of ~20% from 3,000 to 5,000 years ago, coinciding with changes in spring/fall precessional insolation. We find that ENSO variability over the last five decades is ~25% stronger than during the preindustrial. Our results provide empirical support for recent climate model projections showing an intensification of ENSO extremes under greenhouse forcing.