.... now and then of 120 to 130 degrees.  That kills crops and livestock.
Storm surges make coastal cities un inhabitable.
Winter storms killing millions due to massive destruction of power supply and people freezing to death.
Food chain disrupted, due to acidification of the salt water seas, starting with the coastal nurseries that nourish the little fish food and the bird food, working its way up the food chain so commercial fishing is eventually destroyed.  

Life will go on, sorta, but maybe humans get knocked down to a few roving tribes of barbarians wandering from skeletal city to city in ruins.