No. The climate is changing. What I am saying is that one probably cannot definitively say +/- 0.5 degree in , say, the 1600's or 1700's. Add to that. Who was taking said temperature readings???? I know the Royal Navy has been taking readings every watch for hundreds of years, all over the world. How accurate were their devices? Maybe just maybe there is an old 18th century thermometer in working order at Greenwich, that someone can test????
It looks like a nice graph but...