Natural Length of the Current Interglacial

This will be a summary and discussion of Tzedakis et al. 2012. Determining the natural length of the current interglacial. Nature Geoscience 5: 138-141.

Tzedakis et al. (2012) test the overdue glaciation hypothesis by comparing the current Holocene interglacial to similar periods in Earth's history. They use ice cores from which greenhouse gasses have been measured to determine the timing of glacial onset. These results are then used to predict the natural onset of the next glacial cycle.

This paper is interesting in allowing us to contrast the effects of anthropogenic global warming with the potential natural climatic cycles of the Earth. Their comparison to earlier interglacial periods shows that atmospheric CO2 was lower (240 ppmv) than pre-industrial levels (280 ppmv) at the onset of the last glacial. Tzedakis et al. (2012) further state that if comparison to previous periods is valid, modern atmospheric CO2 should have already fallen below 250 ppmv, triggering the next glacial cycle.

I was disappointed that Tzedakis et al. (2012) did not discuss current levels of atmospheric CO2. To me this paper suggests that we cannot expect the onset of a glacial cycle given current global warming (which is obvious). This means that the length of the current interglacial is not a result of low eccentricity, as has been suggested by climate change denialists, but rather of anthropogenic factors.

I suppose this isn't entirely new information, but it is a direct comparison of current conditions to past conditions that highlights the extreme weirdness of today's climate.