Oppo, D.W., Rosenthal, Y. and Linsley, B.K. 2009. 2,000-year-long temperature and hydrology reconstructions from the Indo-Pacific warm pool. Nature 460: 1113-1116.
Oppo et al. derived a continuous sea surface temperature (SST) reconstruction from the Indo-Pacific Warm Pool (IPWP), which they describe as "the largest reservoir of warm surface water on the earth and the main source of heat for the global atmosphere." This history -- which was based on δ18O and Mg/Ca data obtained from samples of the planktonic foraminifera Globigerinoides ruber found in two gravity cores, a nearby multi-core (all at 3°53'S, 119°27'E), and a piston core (at 5°12'S, 117°29'E) that were recovered from the Makassar Strait on the Sulawesi margin -- spans the past two millennia and, as they describe it, "overlaps the instrumental record, enabling both a direct comparison of proxy data to the instrumental record and an evaluation of past changes in the context of twentieth century trends." Reconstructed SSTs were, in their words, "warmest from AD 1000 to AD 1250 and during short periods of first millennium." From the authors' Figure 2b, adapted below, we calculate that the Medieval Warm Period was about 0.4°C warmer than the Current Warm Period.