Christian Science Monitor: Northern-hemisphere temperatures over the past decade are likely to have been warmer than at any time in the past 1,300 years — perhaps over the past 1,700 years if tree rings have anything useful to say about it. Either time span embraces the warmest years of the so-called Medieval warm period. That`s the latest from a team led by Penn State University`s Michael Mann, who heads the university`s Earth System Science Center. And the graph illustrating the take-home message? It still …