Kind of takes the global right out of global warming. While climate variations are never linear, this equates to only a half a degree Centigrade over a century, if you want to play that game. Hardly catastrophic.
Horner doesn't point out the obvious difference between the hemispheres primarily responsible for this dichotomy: the large difference in ocean vs. continental area between the two hemispheres. The ocean is a moderating factor in the warming of the SH.
Climate scientists, of course, are perfectly well aware of this.