Late Paleocene Thermal maximum - A.K.A Global Warming (55.5 million years ago)

We left off 65 million years ago. What else could have happened between that time and now? The Cenozoic was no exception to the mood swings of our planet, though there is a cooling trend present after an initial warming.

Figure 1 shows us what was happening from the end of the Mesozoic to present day, though the Holocene, our present epoch, is almost indistinguishable since it started only 11700 years ago. 

Fig. 1: The δ¹⁸O record shows the temperature scale until around 35 million years ago, before the large scale glaciation of Antarctica and afterwards it reflects the changes in ice volume (towards the left means greater volume of ice). Zachos et al., 2001

The Late Paleocene Thermal maximum, around 55.5 million years ago, saw the highest temperatures in the Cenozoic, with deep sea temperatures rising by 6 °C in less than 10000 years (Zachos et al., 2001). As can be seen in the figure, it also coincided with a significant fall in the δ¹³C records. These characteristics suggest that an immense volume of ¹²C enriched carbon was added rapidly added to the ocean-atmosphere system. Dickens et al. (1997) argue that this ¹²C came from methane clathrates, since it is an immense reservoir (assuming it is similar to present day) that becomes unstable with higher temperatures. However, it remains unclear what could have triggered the initial dissociation of the methane clathrates – model results by Katz et al. (2001) were not conclusive if temperature rise was the initial trigger. Alternative proposed triggers are mechanical disruption of the clathrates, either by seafloor erosion caused by changes in ocean circulation or continental slope failure (Katz et al., 2001), or by bolide impact, though Bowen et al. (2015) did not find it consistent with the two release events of found in their study.

This event can be used as an analogue for present day anthropogenic warming and what we may be facing in the future. This time the trigger for releasing methane trapped in the clathrates is not unknown - the temperature is already rising.