We have made our climb to the top of the geologic time scale, and now we have reached the holocene epoch. Pre-industrial sea level and atmospheric co2 levels are about the same as other interglacials. We now must consider the other kinds of variation that operate on much smaller scales than the glacial-interglacial cycle. Small variations in incoming solar radiation from the sun drive small cooling or warming events on the century scale. Cycles: these variations are on the human and historical time scale, and although they are not big and dramatic, they still affect humans and impact society. Carbon dioxide as of january, 2014 is measured at 400 ppm (you can find these measurements and check out their interactive historical view of rising co2): http://www. esrl. noaa. gov/gmd/ccgg/trends/global. html. How can we answer this question: we can look at the co2 measurements from ice cores drilled in the antarctic and.