The net energy cliff

Charles Hall, the father of the energy return on investment (EROI) concept, once told me that our current society would probably not be able to function if the EROI for the entire society slipped below five. … Hall estimates that the United States is currently running on an EROI of just under 40 to 1. This looks like a fairly substantial margin of safety over the 5 to 1 that might lead to societal breakdown. But worrisome developments in the oil, natural gas and coal fields may send us rushing toward that figure.