The fact is that a rise in ocean temperature will change the magnitude and direction of ocean currents. Whether that rise in temperature is caused by global warming is debatable, but it doesn't hurt to be cautious about it.
It doesnt hurt, you are right. But it isnt something that we should stake billions of dollars on. Im not saying that countries shouldnt engage in global warming/emmisions control but the reasons are more assosiated with many theories, not just one.