Ok, let’s pretend this paper is onto something (yes, I noticed the 2009 date.)
6K warmer than this interglacial. Let’s pretend that Climate Sensitity is 3K (it’s a lot lower.) That’s two doublings of CO2, meaning that CO2 levels were roughly 15-1600 ppm back then.
So either the was a massive human civilzation back then pouring out gigatons of CO2, several times, since there were several interglacials, or a whole bunch of volcanoes poured an insane amount of CO2 into the air without adding the aerosols to cool things (and do it on a cyclical basis,) or…
The CO2 theory is bunk and CO2 is trivially important to global temps. Or this paper is bunk and we move on.
Stable isotope ratios of oxygen and hydrogen in the Antarctic ice core record have revolutionized our understanding of Pleistocene climate variations and have allowed reconstructions of Antarctic temperature over the past 800,000 years (800 kyr; refs 1, 2).
The relationship between the D/H ratio of mean annual precipitation and mean annual surface air temperature is said to be uniform ±10% over East Antarctica3 and constant with time ±20% (refs 3–5). In the absence of strong independent temperature proxy evidence allowing us to calibrate individual ice cores, prior general circulation model (GCM) studies have supported the assumption of constant uniform conversion for climates cooler than that of the present day3, 5.
Here we analyse the three available 340 kyr East Antarctic ice core records alongside input from GCM modelling. We show that for warmer interglacial periods the relationship between temperature and the isotopic signature varies among ice core sites, and that therefore the conversions must be nonlinear for at least some sites. Model results indicate that the isotopic composition of East Antarctic ice is less sensitive to temperature changes during warmer climates.
We conclude that previous temperature estimates from interglacial climates are likely to be too low. The available evidence is consistent with a peak Antarctic interglacial temperature that was at least 6 K higher than that of the present day —approximately double the widely quoted 3 ± 1.5 K (refs 5, 6).
The whole paper is behind a paywall, as usual, but the abstract is here.