Read here. Recently, Phil Jones in an interview with the BBC: "...he agreed that the debate had not been settled over whether the Medieval Warm Period was warmer than the current period." Why would he make such a statement after so many years claiming the opposite?
As Phil Jones knows full well from his own research, the Medieval Warming Period was highly likely to have experienced warmer temperatures than current temperatures per the proxy reconstructions (below graph represents proxy reconstructions only). In a 2003 study that he published with Mann, the proxy reconstructed temperatures clearly show warmer historical temperatures (see blue and green lines on graph below) and that modern temperatures were not accelerating (note steepness of slope of red curve at different points in time) as quickly as they had done in the past.
In addition, when viewing the graphical representation of the proxy temperatures (minus any instrumental temperature records) the claim that modern warming is solely a result of human-CO2, versus all previous historical warmings being the result of only natural forces, is obviously ludicrous to assert. (click on image to enlarge)
"First of all, granting them almost everything they have done, it can readily be seen from their own graph of their own results that the end point of their reconstructed global mean temperature history is not the warmest period of the prior 1800 years. In fact, their treatment of the data depicts three earlier warmer periods: one just prior to AD 700, one just after AD 700 and one just prior to AD 1000...as tree-ring data comprise the bulk of the proxy temperature information employed by Mann and Jones, their reconstructed global mean temperature history must possess a non-temperature-induced pseudo-warming signal driven by CO2- and nitrogen-induced increases in growth that make 20th century warming appear significantly greater than it really is....Their data, however, speak for themselves in clearly demonstrating that late 20th century global warmth was not unprecedented over the past two millennia."
More historical charts here. Other climate history postings here. Modern temperature charts.