GISP2
ice core temperatures show that the arctic was 2 degrees C warmer 6000 years ago, 2000 years ago and approximately the same temperature 1000 years ago (with the Vikings).
A full 900,000 years
of ice core temperature records and carbon dioxide content records show CO2 increases follow increases in Earth's temperature instead of leading them.
As far as determining whether or not CO2 preceded or lagged temperature,
ice core temperature vs. CO2 is self consistent whether or not the dates are wrong.
Unfortunately, they are not well defined on
the ice core temperature proxies due to resolution difficulties and local latitude differences.
More recently, there is the warm period known as the Holocene Optimum (from 3,000 to 8,000 years ago) and shown in
ice core temperatures from Greenland (Figure 4).