Based on the simplifying assumption that the signal can be attributed to temperature change alone, with the effects of salinity and ice volume change ignored, Epstein et al. (1953) estimated that 
a  increase of 0.22‰ is equivalent to a cooling of 1 °C (or 1.8 °F).  
More precisely, Epstein et al. (1953) give a quadratic extrapolation for the temperature, as 
where T is the temperature in °C (based on a least-squares fit for a range of temperature values between 9 °C and 29 °C, with a standard deviation of ±0.6 °C, and δ is δO for a calcium carbonate sample).