atory ▁targets ▁for ▁reducing ▁" green house ▁gas " ▁em issions . ▁Bush ▁stated ▁that ▁human ▁activity ▁had ▁not ▁been ▁proven ▁to ▁be ▁the ▁cause ▁and ▁c ited ▁concerns ▁about ▁the ▁treat y ' s ▁impact ▁on ▁the ▁U . S . ▁economy ▁and ▁pointed ▁out ▁that ▁China ▁and ▁India ▁had ▁not ▁signed ▁on . ▁The ▁Pro tocol ▁entered ▁into ▁force ▁on ▁ 1 6 ▁February ▁ 2 0 0 5 . ▁As ▁of ▁September ▁ 2 0 1 1 , ▁ 1 9 1 ▁states ▁have ▁signed ▁and ▁rat ified ▁the ▁protocol . ▁The ▁only ▁remaining ▁sign atory ▁not ▁to ▁have ▁rat ified ▁the ▁protocol ▁is ▁the ▁United ▁States . ▁ ▁In ▁ 2 0 0 2 , ▁the ▁Bush ▁Administration ' s ▁E PA ▁issued ▁a ▁Cl imate ▁Action ▁Report ▁con cluding ▁that ▁the ▁climate ▁changes ▁observed ▁over ▁several ▁dec ades ▁" are ▁likely ▁mostly ▁due ▁to ▁human ▁activities , ▁but ▁we ▁cannot ▁rule ▁out ▁that ▁some ▁significant ▁part ▁of ▁these ▁changes ▁is ▁also ▁a ▁reflection ▁of ▁natural ▁vari ability ". ▁While ▁the ▁E PA ▁report ▁was ▁initially ▁ha iled ▁by ▁some ▁environmental ists ▁critical ▁of ▁the ▁Bush ▁administration ▁as ▁a ▁" 1 8 0 - deg ree ▁turn ▁on ▁the ▁science " ▁revers ing ▁" every thing ▁the ▁president ▁has ▁said ▁about ▁global ▁war ming ▁since ▁he ▁took ▁office ," ▁within ▁days ▁President ▁Bush ▁dismiss ed ▁the ▁report ▁as ▁being ▁" put ▁out ▁by ▁the ▁b ureau c racy ," ▁and ▁re aff ir med ▁his ▁opposition ▁to ▁the ▁Ky