1 0 , ▁the ▁International ▁Resource ▁P anel , ▁hosted ▁by ▁the ▁United ▁Nations ▁Environment ▁Program me ▁( UN EP ) ▁published ▁reports ▁on ▁metal ▁stock s ▁that ▁exist ▁within ▁society ▁and ▁their ▁rec y cling ▁rates . ▁The ▁P anel ▁reported ▁that ▁the ▁increase ▁in ▁the ▁use ▁of ▁met als ▁during ▁the ▁ 2 0 th ▁and ▁into ▁the ▁ 2 1 st ▁century ▁has ▁led ▁to ▁a ▁substantial ▁shift ▁in ▁metal ▁stock s ▁from ▁below ▁ground ▁to ▁use ▁in ▁applications ▁within ▁society ▁above ▁ground . ▁For ▁example , ▁the ▁in - use ▁stock ▁of ▁co pper ▁in ▁the ▁USA ▁grew ▁from ▁ 7 3 ▁to ▁ 2 3 8   kg ▁per ▁cap ita ▁between ▁ 1 9 3 2 ▁and ▁ 1 9 9 9 . ▁ ▁The ▁report ▁authors ▁observed ▁that , ▁as ▁met als ▁are ▁inher ently ▁rec y cl able , ▁the ▁metal ▁stock s ▁in ▁society ▁can ▁serve ▁as ▁huge ▁mines ▁above ▁ground ▁( the ▁term ▁" urban ▁min ing " ▁has ▁been ▁co ined ▁with ▁this ▁idea ▁in ▁mind ). ▁However , ▁they ▁found ▁that ▁the ▁rec y cling ▁rates ▁of ▁many ▁met als ▁are ▁very ▁low . ▁The ▁report ▁war ned ▁that ▁the ▁rec y cling ▁rates ▁of ▁some ▁rare ▁met als ▁used ▁in ▁applications ▁such ▁as ▁mobile ▁ph ones , ▁battery ▁pack s ▁for ▁hy brid ▁cars ▁and ▁fuel ▁cells , ▁are ▁so ▁low ▁that ▁unless ▁future ▁end - of - life ▁rec y cling ▁rates ▁are ▁dram atically ▁stepped ▁up ▁these ▁critical