A review of the global extent of the MWP is presented and the following conclusions are offered:
- The MWP was a global event and a large number of studies show that warming events overwhelming outnumber cold events.
- However, the not insignificant number of dry or wet events recorded in the MWP Mapping Project would suggest that perhaps the Medieval Climate Anomaly would be a better description than the MWP.
- NH temperatures during the MWP were at least as warm those in 1980-1989 instrumental record.
- Recent instrumental temperatures show higher temperatures when compared with the MWP proxies. However, instrumental temperatures should not be compared directly with proxy temperatures because this is not an “apples for apples” comparison. Proxy temperatures are dampened (flattened) out on decadal or greater scales.
- Recent proxy records diverge from instrumental temperatures – instruments show higher readings when compared with proxies.
- The divergence problem in item (e) above is probably due to a linear proxy-temperature response being assumed in current temperature reconstructions. A nonlinear proxy-temperature response would achieve more accurate results for historical high and low temperatures and achieve a better correlation with recent instrumental data.