We @thefosterlab, with Celli Hull, Dan Lunt, and Jim Zachos organised a discussion meeting at the Royal Society last September to bring together scientists from many branches of the Earth Sciences to advance our understanding of these events and crucially try and fathom what they can tell us about our warm future. This research has now been written up and turned into a special volume of the Philosophical Transactions of the Royal Society (here). I recommend you go and read them as many are open access and free to download.

(Briefly) What can we learn from hyperthermals?

Exactly how the climate will respond to anthropogenic forcing is currently uncertain because our understanding of the climate system is incomplete. Hyperthermals, however paint a very consistent picture of how the Earth has responded in the past intervals of rapid and massive carbon addition (see table above). These features include:

(i) rapid global warming of >3 C.

(ii) a reduction in oceanic oxygen content leading to ocean anoxia and/or euxinia.

(iii) ocean acidification of around 0.3 to 0.4 pH units.

(iv) the hydrological cycle intensified with wet regions generally getting wetter and dry regions drier.

(v) continental erosion/weathering rates were enhanced.

(vi) relatively large biotic responses occurred in the first half of the Phanerozoic (Paleozoic and early Mesozoic mass extinctions often associated with hyperthermals), and muted or mixed responses in the latter half of the Phanerozoic. But in each case the hyperthermals are associated with biotic disruptions.

(vii) the Earth system takes 100's of thousands of years to recover once C-emissions have stopped.

These changes to the system were likely caused by the introduction of 10,000 to 40,000 Pg of C over a couple of millennia. Where this carbon came from is debatable but CO2 from flood basalt eruption and emplacement is likely involved (see here and here). Although this is rapid for geology, the rates of carbon addition are still likely 10x less than current rates (i.e. less than 1-2 Pg C per year vs. 10 Pg C per year; though this is controversial – see this paper in our special volume).