Four year old screaming when baby cries

Whenever we are in the car and our 6 month old starts to whine or cry, our four year old starts screaming at the top of his lungs and won’t stop. He does this at home as well, but at least we’re able to move away from his noise. I’m concerned his loud screaming in the car is going to damage our baby’s ears. Is that likely? How do we stop him? We tried headphones and he won’t keep them on. We have to drive 30 minutes every day for school, grocery shopping, etc.