Garrett Hardin’s classic essay, ‘The Tragedy of the Commons’ (1968), eloquently expresses the finite nature of the non-renewable resource base on which human technological society depends: “In a finite world...the per capita share of the world's goods must steadily decrease”. The Human Natural Resource Endowment (HNRE) is a measure of the per capita allocation of resources worldwide. Publicly available data documenting annual production of 40 metals and metalloids (i.e. rare earth elements) were used to calculate the HNRE of metals from 1900-2018. Since 1900, at least 8.07 x 10¹⁰ metric tonnes of metal were produced worldwide. Between 1900 and 2018, the observed annual rate of consumption of metals increased exponentially at 3.75% annually. Thus, production of metals doubles in approximately 18.7 years and global metal production has doubled more than 6 times in 118 years. Despite exponentially increasing production of metals since 1900, HNRE steadily declined because population also increased exponentially. The present HNRE for metals is 9.53 metric tonnes per person. In 2018, remaining global metal reserves were 7.45 x 10¹⁰ metric tonnes (i.e. approximately 10 metric tonnes per person). Consequently, extrapolation of HNRE into the future using the historic rate of metals production and HNRE decline shows HNRE reaches zero in 2021! However, HNRE depends critically on estimates of the Ultimately Recoverable Reserves (URR) of each metal and these estimates may be quite uncertain. In addition to uncertainty in resource assessments, reserve and production data for some metals are classified national security secrets. To account for potential errors and omissions in global metal reserves estimates, additional depletion scenarios were modeled using URR 2 – 10 times greater than present estimates. Model results indicated that increasing estimated URR even 10-fold provides only a few additional years prior to depletion. Further, it may be surmised that HNRE falls below the necessary threshold to sustain humanity at a quantity significantly greater than zero. As such, the declining trend of HNRE indicates that global metal resources may be essentially ‘exhausted’ prior to 2035 and that societal use of global metal resources is unsustainable.