That can only be passed through congress and they already told Obama they would not pass any treaty that jeapordized the second amendment.
And even if they did, do you think the largest army in the world (armed US citizens) would give up their guns without a fight? Also, in so much as every congressman, law enforcement officer, and military individual pledged to defend the Constitution of the United States of America from all enemies both foreign and domestic, who would enforce such an action which directly violates the Constitution?