How Humans Took Control of Climate

Session Date: 
May 15, 2015

Until the last decade, the consensus opinion had been that significant human effects on greenhouse gases and climate began during the Industrial Era (the last 200 years). But this paradigm is under assault based on evidence from several fields of research that suggests human intervention in the climate system thousands of years ago. Greenhouse-gas concentrations measured in bubbles of ancient air trapped in the Antarctic ice sheet show that carbon dioxide (CO2) and methane (CH4) concentrations fell during the early parts of previous interglaciations, but have risen during this one since 7000-5000 years ago. This ‘wrong-way’ (upward) trend suggests that early farming emitted large amounts of CO2 and CH4, with a warming effect on climate. In addition, comprehensive summaries of ‘ground-truth’ evidence from archeology and paleoecology in Europe and China reveal large-scale CO2-emitting forest clearance and CH4-emitting rice irrigation thousands of years before the industrial era. This evidence rules out the previous paradigm and favors a much earlier influence.

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