Why Aren't We Warmer than the Last Interglacial?
If you look at graphs of global mean surface temperatures that go back to the last interglacial (LIG or the Eemian), you may notice that GMST anomalies were higher then than during the current interglacial (the Holocene), and current warming has not yet eclipsed the warmest periods of the Eemian. It's a fair question to ask, given that CO2 was ~280 ppm both during the Eemian and the Holocene (and over 420 ppm now), why aren't we yet warmer than the Eemian? The answer to this needs to be given in two parts. First, we'll look at why GMST during the Eemian was warmer than during the pre-industrial Holocene, and second, we'll consider why current warming has not yet eclipsed Eemian warmth. Long-term changes in GMST occur as a result of the energy imbalance near the top of the atmosphere, and on time scales of tens to hundreds of thousands of years, orbital cycles play a significant role in determining these GMST changes and the glacial cycles of the Quaternary. In fact, t...