third ▁of ▁the ▁glo be , ▁with ▁a ▁" sw amp " ▁ocean ▁and ▁only ▁land ▁surface ▁at ▁high ▁lat itudes , ▁it ▁showed ▁an ▁Ar ctic ▁war ming ▁faster ▁than ▁the ▁trop ics ▁( as ▁have ▁all ▁subsequent ▁models ). ▁ ▁Am pl ification ▁ ▁Am pl ifying ▁mechan isms ▁Fe ed back s ▁associated ▁with ▁sea ▁ice ▁and ▁snow ▁cover ▁are ▁widely ▁c ited ▁as ▁the ▁main ▁cause ▁of ▁recent ▁terrest rial ▁polar ▁ampl ification . ▁However , ▁ampl ification ▁is ▁also ▁observed ▁in ▁model ▁world s ▁with ▁no ▁ice ▁or ▁snow . ▁ ▁It ▁appears ▁to ▁arise ▁both ▁from ▁a ▁( poss ibly ▁trans ient ) ▁intens ification ▁of ▁pole ward ▁heat ▁transport ▁and ▁more ▁directly ▁from ▁changes ▁in ▁the ▁local ▁net ▁radiation ▁balance ▁( an ▁overall ▁decrease ▁in ▁out ward ▁radiation ▁will ▁produce ▁a ▁larger ▁relative ▁increase ▁in ▁net ▁radiation ▁near ▁the ▁pol es ▁than ▁near ▁the ▁equ ator ). ▁ ▁Some ▁examples ▁of ▁climate ▁system ▁feedback s ▁thought ▁to ▁contribute ▁to ▁recent ▁polar ▁ampl ification ▁include ▁the ▁reduction ▁of ▁snow ▁cover ▁and ▁sea ▁ice , ▁changes ▁in ▁atmos pher ic ▁and ▁ocean ▁circul ation , ▁the ▁presence ▁of ▁anth rop ogen ic ▁so ot ▁in ▁the ▁Ar ctic ▁environment , ▁and ▁increases ▁in ▁cloud ▁cover ▁and ▁water ▁v apor . ▁Most ▁studies ▁connect ▁sea ▁ice ▁changes ▁to ▁polar ▁ampl ification . ▁Some ▁models ▁of ▁modern ▁climate ▁exhib it ▁Ar ctic ▁ampl ification ▁without ▁changes ▁in ▁snow ▁and ▁ice ▁cover . ▁The ▁individual ▁processes ▁contrib uting ▁to ▁polar ▁war