As icebergs melt, at least two bad things happen. The first is they have less surface area to reflect the sun’s rays meaning the ocean receives more of these rays and in turn this warms the earth more than usual.
The second is they change the saline levels of the ocean which could totally change the flow of ocean currents which control the weather patterns of the world. If you wonder why the weather has been getting wacky lately, it is likely because the icebergs are melting rapidly and the oceans are getting less salty.