Global Carbon Cycle Change: a Geological Perspective on Carbon and Climate

Our global clean energy goals are really about controlling carbon fluxes. The basis for any expectation that we can achieve sustainability is our understanding of the Earth's natural carbon cycles. To change global climate, the amount of carbon dioxide and other greenhouse gases in the atmosphere needs to change, which in turn requires a change in the way carbon is moved around among the various forms and places it exists in and on the Earth.  If one looks backward millions (and billions) of years into deep geologic time, and compares the Earth to other planets, it is possible to grasp how carbon can be moved in and out of planetary interiors, and how natural cycles have acted to regulate the Earth's surface temperature. Although many of the details are uncertain, evidence indicates that natural processes have produced large changes in the amount of atmospheric CO2 in the geologic past.  But, an essential aspect of geologic processes is that they act extremely slowly, even during times regarded as examples of rapid change.

In contrast, over the past 100 years Earth's carbon cycles have undergone revolutionary change as a result of an unprecedented transfer of carbon from geologic storage to the atmosphere. Today, 98 to 99% of the net movement of carbon out of geologic reservoirs into the atmosphere is due to human activities; there is little uncertainty in this estimate.  Whether you think this is a problem or not, it is nevertheless a fact that we are currently doing something that is unprecedented in Earth history; unprecedented not just in the past million years, but in the entire history of the planet.  Engineering a sustainable carbon cycle may be attainable over the next century or two, but could entail significant surprises depending on whether we adequately understand the Earth's carbon cycling systems.

Speaker: Donald DePaolo