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.

Tweet of the week - Another record year?

A new year begins, so it is almost time to see how 2014 measures with previous years - did the warming trend continue?

Will 2014 be the warmest year on record? Watch this space #climate2014 pic.twitter.com/6kF4rZDs7M
— WMO | OMM (@WMOnews) January 2, 2015

To the surprise of all (... not really), the Earth continued warming. At the beginning of December, the WMO issued a press release that stated that, if 2014 continued the same trend in November and December as what was observed from January to October, it would be among the hottest - if not the hottest - year on record. Global air average temperature (Jan-Oct) was 0.57°C higher than the 1961-1990 reference period. Over land average air temperature was 0.86°C higher.

 

Average temperature over land will continue warming faster that over the sea. Figure 1 shows the change in surface temperature per degree Celsius of global mean change, as projected for the 21st century (IPCC, 2013).

Fig. 1: mean surface temperature increase per °C of global
mean temperature increase. Source: IPCC, AR5

 

This means that the average global temperature is just that, an average. A warming in 2°C is not distributed equally around the globe, but there can be cooler areas and other areas that are much warmer. While the globe may increase 1°C, the continents will be around 1.25-1.5°C warmer. The figure also shows that the warming will be even higher in the Arctic regions, because the localised ice-albedo feedback will allow an increase in absorbed radiation.

 

The final verdict on 2014 is still to come, but it will likely not be a surprise.