Which sentence shows a flaw or mistake in logic

1) A volcano eruption in the early 1800 through so much ashen to the air that causes global temperature dip
2) sunspot activity affects earths climate which means that human activity is not a factor
3) ice reflects more heat away from the earth then open water which absorbs heat when is it exposed to sun
4) Ocean currents such as the golf stream and the Labador current have a significant effect on local climates