To my 5-year-old son:

By the time you’re my age, the year will be 2051. I don’t know what the planet will look like. And that scares me.

Today, it’s obvious that nature is changing too fast, too much. Of course, nature’s not the culprit. We are. Humans. Your parents, your grandparents, and so many generations who came before us.

We’ve been selfish and careless. We’ve forgotten to think about the future. We’ve screwed up the environment with our plastic water bottles and our massive landfills, and most of all, our fossil fuels.

If we don’t make real changes, and soon, our Earth in 2051 may look very different from our Earth in 2018. I have to fight for your future. There’s no other reasonable choice, for me or any adult.

What am I fighting for? I want you to share these four moments with your own kids, in 2051.

1. Hikes in the woods, among the trees and the bluebells, deer peeking out at you through the brush, birdsong floating all around us. I want you and your kids to love to explore the woods. Climate change causes droughts and forest fires. It threatens our whole ecosystem in countless ways, endangering too many species, particularly bees and butterflies and other pollinators (which are vital to our eco-system). I will fight for your future forests.

2. Fun at the beach. The beach is my favorite thing in the world, other than you and your dad. I’m in awe of the vastness of the ocean. As I dig my toes into the sand, I feel connected to the Earth. Like I belong. I want you to have those long, lazy summer days at the beach, swimming and body surfing, stretching out on a towel to read a book, and building sandcastle after sandcastle. But climate change threatens beaches, with tides rising and coastlines eroding, whole cities disappearing. I will fight for your future beach days.

3. Snow. I remember taking you out in the snow for the first time. It was magical. I want you to experience that same magic with your children. But as temperatures soar, winters in many parts of the world will be under siege. Winter freezes could shrink or disappear. I will fight for your future snowball fights.

4. Lazy summer days. I want you to love summer as much as I do. It’s my favorite season. I love to lie outside in the sun, to feel the sunlight soaking into my skin. I love that warmth. Summer is your favorite too. You say, “I like it hot.” But if we do nothing, your favorite season could become miserable, oppressive. You might not want to run around in the sprinklers with your kids. I will fight for your future long days of summer.

The good news is that it’s not too late. We can change our ways. We can give you a wonderful future.

We can demand clean energy. We can conserve energy. And recycle. And compost. And clean up litter. And eat less meat. And use public transportation. And drive cars that pollute less.

All these big and little choices make a difference. If we all do our parts to help — and if our governments do theirs — we can give you a beautiful, healthy planet in 2051. Along the way, we can teach our children how to make good choices, how to be part of the solution instead of part of the problem.

You and me kid, we can save the world. We have to try.