Background
When considering the subject of global warming, and especially when considering ways to change the way the world does business (emits CO2 to the atmosphere) based on purported changes in global temperature, it is only prudent to have a good global record of temperature over as long a time period as possible.  Currently, we are not in great shape in this regard; for the temperature history most commonly employed in these deliberations (Mann et al., 1999) pertains to only a portion of the land area of the globe, which is but a portion (and a minor one at that) of the entire "water-world" we call earth.  Hence, it is absolutely essential that we obtain more long-term sea surface temperature (SST) data, which is what the study of Linsley et al. does.  A second important reason for obtaining such data is that the information could greatly increase our knowledge of the ability of coral reefs to withstand the thermal stresses they are predicted to encounter in the face of the CO2-induced warming of the globe that the IPCC claims is already upon us.

What was done
The authors retrieved a 3.5-meter core of continuous coral from a massive colony of Porites lutea on the southwest side of Rarotonga, which is located at 21.5°S and
159.5°W in the Cook Islands.  They measured Sr/Ca ratios on 1-mm-interval sections spanning the entire core (representing 271 years of growth), as well as delta ¹⁸O values at the same resolution from 1726 to 1770 and from 1950 to 1997 for calibration purposes that also utilized Integrated Global Ocean Service System Products SST data.

What was learned
Astonishingly - but, then again, maybe not so surprisingly - the authors' analyses revealed the existence of a quarter-century period centered on about the year 1745 when SSTs in the vicinity of Rarotonga were at least 1.5°C warmer than they are today, which is pretty amazing in light of the Mann et al.-inspired claim of the IPCC that the current mean temperature of the globe is higher than it has been at any time in the past millennium.

What it means
The results of this study raise serious questions about the validity of the "global" temperature history that is being used to cajole the nations of the earth into accepting a planet-wide scheme for reducing anthropogenic CO2 emissions to the atmosphere.  This history is derived from but a few records, which by virtue of their paucity can in no way be construed to represent the globe as a whole; and the study of Linsley et al. demonstrates that superb data from one previously-unsampled part of the planet tell a drastically different story from the one IPCC politicos are trying to feed us.  It would seem only prudent, therefore, to delay judgment on this important matter until more long-term coral-derived temperature data are acquired.  In the words of Cane and Evans (2000), who provide an interesting perspective on the Linsely et al. paper, "fewer than 100 comparable records should be enough to fill in the big picture" with respect to modes of decadal variability.  They would also go a long way towards verifying or vilifying the temperature history of Mann et al.

In this regard, it would also seem prudent to temper our angst over the potential of predicted global warming to drive earth's corals to extinction, as is so fashionable to claim nowadays.  On the basis of the temperature record of the Linsley et al. study, which Cane and Evans characterize as "persuasive," we know that corals in the vicinity of Rarotonga have survived sustained temperatures of a magnitude easily great enough to destroy them, according to conventional Greenpeace wisdom.  Perhaps the politically-correct view of the world's temperature history, both future and past, as well as the IPCC's take on the resiliency of its biota, are a long way removed from reality.

Mann, M.E., Bradley, R.S. and Hughes, M.K.  1999.  Northern Hemisphere temperatures during the past millennium: Inferences, uncertainties, and limitations.  Geophysical Research Letters 26: 759-762.