The report in Nature Climate Change was for one specific tree ring set in northern Norway. It's probably stretching the evidence too far to try an apply this to the Northern Hemisphere. There's an interesting discussion of the paper by Michael Mann here:
http://www.realclimate.org/index.php/archives/2012/07/tree-rings-and-climate-some-recent-developments/CO2 emissions have dropped significantly due to the ongoing switch from coal to natural gas. But in the long run that won't be enough. Unless we reduce our net emissions of CO2 to zero the problem of global warming just keeps getting worse.
