1 - Carbon Accounting for Planet Earth

Summary

The Earth surface carbon cycle consists of regular flows between the major sinks: atmosphere, ocean, soils and biota. It is in balance, except for flows to and from long-term storage (methane formations, deep ocean, lithosphere), which comprise the deep Earth carbon cycle. At the beginning of life in earth history, about 500 million years ago, the atmosphere was carbon-rich, and Earth temperatures were vastly hotter than today. Over time most of this carbon was withdrawn from the surface carbon cycle through ocean sedimentation, reactions with weathering rock and migration of organic matter to the lithosphere, where they were transformed into fossil fuels. This eventually produced the temperate Earth, which facilitated human evolution, but now, by extracting and burning fossil energy, humans are recreating conditions for the hotter Earth of earlier times. These direct carbon emissions can be amplified by feedback mechanisms, whereby initial warming releases carbon stored in formerly stable methane deposits and alters the carbon cycle so as to increase the size of the atmospheric sink relative to other sinks or changes in the Earth’s albedo. The politics of controlling emissions is further complicated by lags in warming and subsequent climate impacts.