"Relative warmth" means that something or someone is warmer compared to something else, but it doesn't necessarily mean it is always warm. Full definition
Given that, their estimate of relative warmth in 2009 is probably a good bet. (realclimate.org)
But Mann points out that neither «we, nor any other researchers, have ever denied there was a period of relative warmth sometime during medieval for many regions. (theguardian.com)
Period of relative warmth in some regions of the Northern Hemisphere in comparison with the subsequent several centuries. (realclimate.org)