Green Boy by Susan Cooper

Trey and his mute, little brother love to explore the little island near their home in Jamaica. Their grandparents allow them to row over to the cay where they enjoy the birds, fish, and their own private cave. Then one day in the cave, the light starts to shimmer, Trey hears a sound, and the boys find themselves transported sometime in the future. The plants have been cut down, buildings and roads have taken their place, and all of the animals they knew are gone. Developers have destroyed all the beautiful nature of the island, and Trey discovers that his silent brother is the only one who can make things right.

Man versus nature. Man versus society. It's hard to stop businesses when they promise people money. The author captured the confusion, frustration, and determination of the two brothers. Little brother Lou had a lot to say even though he couldn't speak. It was amusing that Trey could panic, but Lou would just smile and make things better. The plot skips back and forth in time, as the kids try to figure out how to stop the future society.