There is absolutely no doubt that exposure to noise levels in excess of 100 db causes cumulative hearing damage. Worse yet, this is hearing loss that you can never recover. Once it goes away, it's gone forever. Eventually you are likely to develop tinnitus, a constant 'singing' or 'whistling' in your ears that overlays everything you hear. No fun.
The best solution is a pair of custom fitted earplugs made by an audiologist. These are cast out of space age polymers from molds made in your own ears and contain a tiny valve that allows low level sounds to be heard, while at the same time cutting out everything that's above a given sound pressure. You can still hear sirens, horns, and so forth, but the wind noise is pretty much gone. (And that constant wind noise really tires you out. Try it and see.) Best of all, these things are legal -at least in California- under the provisions of the law, whereas store-bought plugs are not. However, many riders use disposable store-bought plugs and are quite content with them. They can be found in the pharmacy section of many stores.
For lots more information, read IanJ's comprehensive survey of earplug models.