That sound you just heard was Al Gore's head exploding. Here's the money quote from the paper;
"Our most recent crystals suggest a warming relative to
the LIA in the last century, possibly as part of the regional recent
rapid warming, but this climatic signature is not yet as extreme in nature
as the MWP."
To summarize, our current warmth ain't nothing compared to the Medieval Warm Period, when Vikings farmed Greenland where now there is only permafrost. Today not only is farming impossible with manual tools, there's no way to dig a grave with a shovel through that frozen earth. Vikings buried their dead there for nearly 400 years, and they didn't have the benefit of a Caterpillar-built backhoe to do it. If global warming covered the entire planet during the MWP, then the causal factor cannot, must not be CO2! It must be exterior to the planet's ecosystem. Or in other words, it's the sun.