Antarctic isotopic thermometer during a CO2 forced warming event

Results from an isotope-enabled general circulation model are presented in order to determine the isotopic signal of a warmer climate on Antarctica. The warming is forced using CO2 forecasts for the next century. For unforced interannual climate variability the temporal gradient and correlation between stable water isotopes and surface temperature is small. The relationship is much stronger for the CO2 forced event. There is little regional coherence between temporal gradients for the forced and unforced climates, implying that correlations between stable water isotopes and temperature from instrumental records of a couple of decades cannot be applied to larger warming events. Additionally, there are strong discrepancies between the forced warming temporal gradients and present-day spatial gradients of isotopes against temperature. We show that it is difficult to obtain a local spatial gradient since it is systematically affected by the geographical size of the spatial sample. For the forced warming, the temporal gradient derived for the warming event over Dome C is less than half the value generally applied. We determine, through means of a new frequency decomposition, that a large portion of this decrease from the expected value is due to changes in the seasonal precipitation temperature covariance. This low isotopic sensitivity to a CO2 driven warming implies that current and future warming trends may have rather small isotopic signals in Antarctica.

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