Saying we shouldn't be doing something to alleviate climate change because we can't precisely predict what the effects will be, is like saying that because we can't predict exactly what will happen, we should not step on the brakes when our car is headed for a brick wall. Exactly what will happen at a given speed will depend on how the car is made, if it has been weakened by age or accidents, the strength of the wall. But it would be totally stupid not to stop the car before we hit the wall.
A ploy the fossil fuel industry has recently been trying is to try to convince people that since a certain amount of damage has already been done, we shouldn't try to prevent even more. That is like saying that if we are headed for a brick wall, and won't be able to avoid hitting it, we shouldn't try to slow down the car as much as possible, to lessen the damage.