This is good as a 8 years old boy, Carry on to encourage him to participate more to write, or let him express him self in his own opinion in all different area. Such as, The politicical, the society, the community, the family, etc....

This will initiate him, how should he think or judge in the maters that all around.

Suggest to keep this letter, and show it to him every two years after, let him read it again.(or ask him rewrite the same letter), By doing this, It will reminds him, what he was thinking when he was 2 years younger.

I believe he will re-think what he said on the 1st letter. Doing this, he will be able to judge that. did he say it correctly or worng,(When he was 2 years younger) because he has learned more, have more experence in his young life, in turn, his judgement will have more elemant to use to make the opinion.

This is great for an 8 year old, but please consider the facts. For your first paragraph, you wanted to stop producing gasoline cars. This is an good idea but what happens when solar cars become popular? The gasoline cars end up in a landfill, or the furnace. That's a waste of metal, and effort. Also, what happens to the gas stations? They will become bankrupt because no one wants to go there because all the cars are solar powered.

Your second paragraph was also good, but then an over dosage of carbon dioxide will harm the trees. And there isn't a point in doing this because at night the trees will breathe the carbon dioxide back out. And if the trees get harmed, what happens to the paper industry? The paper we use may become frail or even turn black.

Your third paragraph is great though. However, your idea is already in use. Some universities have a program where people plant trees, and some groups have been made to plant trees as well.

As perent. it is our responsbility to teach our kid. What and How should judgement is made when they seeing things.
No matter how good or smart they are now, All are only from their young age's experence,(westen expression they still "Green"). right or worng. time will tell as they grown up. As perent's we have to guide them out as they growing up.