Goodbye view from the back porch

Our neighbors in back plan on cutting down these trees just beyond the fence at the back of our yard. We live on the second floor and have enjoyed this view and the privacy it has provided us in a thickly settled city environment for almost 40 years.

To add insult to injury, they have asked if they can cut them down from OUR yard. I try to be neighborly but this is asking too much. I may not be able to stop them, but I don't have to make it easier, do I??????