Asymmetric extreme events of Earth's climate and carbon cycle during the last 66 million years

The history of Earth's climate and carbon cycle is preserved by carbon and oxygen isotope records in deep-sea sediments. Here we show that the sub-Myr fluctuations in both records have exhibited pronounced, negatively skewed non-Gaussian tails throughout most of the past 66 million years. This asymmetry suggests that the climate-carbon cycle system has been intrinsically predisposed towards extreme events involving abrupt global warming and respiration of organic carbon. The fluctuations further obey theoretical relationships predicted for stochastic multiplicative noise processes. We investigate these observations by developing a simple climate-carbon cycle model in which the amplitude of random internal fluctuations increases at higher temperatures. The model replicates the data well, provides a general explanation for the observed pacing of past global warming events by changes in orbital parameters, and is complementary to approaches that seek to explain these events on an individual basis. These results suggest that, as anthropogenic emissions continue, Earth's climate may become more susceptible to extreme warming events on geological timescales.