Now, I'll go along with you. There is probably an increase in the global mean temperature of around a degree celsius. I say "probably" because, first, accurate data from the "medieval warm period" simply does not exist; second, the instrumentation used today is much more accurate and widespread than even that used in the 1920s; and third, even the chart you provided shows global temperature cycles (sort of). One cycle does not a pattern make, but it is compelling.
My gentle reminder to you is that funding for things scientific is ALWAYS political. As there is political pressure towards man-made global warming, public research funding will ALWAYS go in that direction. I speak from direct, personal experience; not GW, but in another realm altogether. Hence the need for organizations formed to "deny" MMGW.