Background
The authors write that "high-resolution records of climate change during the Holocene are valuable for a better understanding of ... present-day climate conditions and the potential trend of future climate change." This statement is especially applicable to the tropical Western Pacific (which is located adjacent to the South China Sea), for in an attempt to depict earth's current temperature as being extremely high and, therefore, extremely dangerous, Hansen et al. (2006) have claimed that "this critical ocean region, and probably the planet as a whole [our italics], is approximately as warm now as at the Holocene maximum and within ~1°C of the maximum temperature of the past million years [our italics]."

What was done
Wei et al. reconstructed three mid-Holocene sea surface temperature (SST) records that spanned more than 30 years using Sr/Ca ratios derived from cores of three Porites lutea colonies in the fringe reef at Dadonghai, Sanya in southern Hainan Island, which lived about 6000 years ago at a water depth similar to that of modern coral at that location (approximately 18°12'N, 109°33'E).

What was learned
In the words of the six researchers, "the results indicate warmer than present climates between circa 6100 yr B.P. and circa 6500 yr B.P. with the mid-Holocene average minimum monthly winter SSTs, the average maximum monthly summer SSTs, and the average annual SSTs being about 0.5°-1.4°C, 0°-2.0°C, and 0.2°-1.5°C higher, respectively, than they were during 1970-1994." In addition, they report that "ENSO variability in the mid-Holocene SSTs was weaker than that in the modern record, and the SST record with the highest summer temperatures from circa 6460 yr B.P. to 6496 yr B.P. shows no robust ENSO cycle."

What it means
The findings of Wei et al. clearly contradict the extravagant contention of Hansen et al. (2006) with respect to the current degree of warmth of western equatorial Pacific SSTs, which contention Hansen (2007) reemphasized in his 26 April 2007 testimony before the Select Committee of Energy Independence and Global Warming of the United States House of Representatives. In addition, computer model simulations have suggested that global warming will increase both the frequency and intensity of ENSO events; but the data of Wei et al. demonstrate that this claim, too, is incorrect. In fact, a wealth of empirical evidence demonstrates that just the opposite is the case (see ENSO (Relationship to Global Warming) in our Subject Index). Consequently, Wie et al.'s finding that ENSO variability in the mid-Holocene "was weaker than that in the modern record," and their observation that "the SST record with the highest summer temperatures from circa 6460 yr B.P. to 6496 yr B.P. shows no robust ENSO cycle" also suggest that it is currently not nearly as warm in the western equatorial Pacific as it was during the mid-Holocene.

Reference
Hansen, J., Sato, M., Ruedy, R., Lo, K., Lea, D.W. and Medina-Elizade, M. 2006. Global temperature change. Proceedings of the National Academy of Sciences USA 103: 14,288-14,293.