Climate science has produced two contrasting frameworks to explain the ‘ice age’ climate cycles of the recent geologic past. Either orbital forcing encouraged the growth and decay of ice sheets that reflect sunlight to cause ice age cooling (Milankovitch theory), or changes in atmospheric CO₂ affected Earth’s greenhouse effect to drive global climate change (CO₂ theory). Overwhelming evidence from observation, simulation and theory suggest that both these dynamics operate in Earth’s climate system. In the main part this talk I will use elements of General Systems Theory to assess causality of climate change in the Earth System, and present boron isotope records that identify surface ocean pH change as the necessary and sufficient condition for ice age cycles and anthropogenic climate change. Further, we have developed observations and theory to demonstrate that the common attractor for ocean pH, atmospheric CO₂ and climate states is an Earth property that emerged as recently as 1 million years ago, during the mid-Pleistocene climate transition (MPT). This new perspective on the coupling of climate and carbon cycle can be useful in weighing purposeful interventions to mitigate anthropogenic climate change and ocean acidification, where Earth System models serve as a critical means of knowledge production. To broaden participation in climate solutions will require making these models accessible and engaging across a wide range of contexts.

Lunch served.