Participants joined together to strike ahead of next week's UN Climate Summit and NYC Climate Week, urging lawmakers to act on climate issues.
More than 1,000 communities across the United States participated in the event, and New York City schools allowed students to attend the march.
Sixteen-year-old activist, Greta Thunberg, spoke with "Good Morning America" about her plan for the Climate Strike and the message she wants to send to others about climate change.
GMA: What is your plan for today's Climate Strike?
Greta: Today I'm going to join the Climate Strike in New York, which will start on Foley Square and end up on Battery Park, and then I'm planning to go home and look at all the pictures from around the world from all of the strikes.
I look forward to doing that and to seeing all the numbers from strikes.
GMA: What do you expect from today?
Greta: From today, I hope there will be lots and lots of people all around the world who are standing together and are striking for the climate, striking for schools, striking from work. People of all ages joining each other in this fight, and I hope that will lead to action, to real action, because this is building up to the UN Climate Action Summit on Monday and for the UN Week when world leaders are gathering in New York. I just hope that they will take something out this that there are so many [who desperately] want action, who demand action.
GMA: We heard that over 150 countries are participating in this Friday, how does that make you feel?
Greta: The numbers from all these cities around the world. There are tens of thousands and just small towns, and it's just incredible to see. I think it's just a joyful day.
GMA: What's your next step?
Greta: After today, I am going to stay in New York for a while for the UN Week and join several events, and then for the big strike on the 27th of September in one week, I am going up to Montreal to join that climate strike, and then I'm going to try to get to Santiago.
This movement we are planning on continuing. [For] some of us, it's every Friday and some of us, it's whenever we can and many of us on the big global strikes.
GMA: You recently mentioned that news organizations and Congress need to do more than just cover you like a piece of news. Tell us more about that.
Greta: Right now we are focusing very much on me as the individual, and not the climate crisis itself, so I think we need to see more the big picture and the media need to cover this whole crisis for what it actually is.
I'm so public and so many people are listening to me, then I'm trying to use that positioning to making a change.
GMA: Tell us about a time during your tour when you spoke to someone who opposes your beliefs.
Greta: Of course, I have met many people who don't understand or accept the science, and I just don't try to convince them otherwise, because I don't want to normalize their view, because, I mean, it's just science. This is not my beliefs or opinions. I'm just trying to communicate the science.
GMA: Do you feel like when you talk to people in America, it's different than anywhere else you've traveled to.
Greta: Of course, every country's different. Here, it feels like we are still stuck in the conversation of whether the climate crisis is real or not. People always say, "I believe in climate change," and it's just we need to move past that.
GMA: What don't people understand about your mission?
Greta: About me and our mission, this movement's mission, we are not just some kids who are skipping school, but this actually something much bigger. This is a movement and all we're saying is, "Listen to science," and we are so much more than just young children. This is, I think, this is something very big that is growing and it will not stop. I think we are only seeing the beginning.
GMA: What would you want to happen in 50 years?
Greta: I would want [the world] to have taken the responsibility and listen to the science, and together with experts and scientists, developed a plan and how to take the measures required to safeguard the conditions for future and present generations.
GMA: Do you have a message for the leader of the United States, President Donald Trump?
Greta: My message is the same to everyone, just [unite behind] science, and, I mean, it doesn't feel like it's very easy to change his mindset, so I'm not even gonna try to do that.
GMA: What do you think the best way is to get people to agree or talk about climate issues?
Greta: I think just raise awareness and start treating this crisis as the crisis it is, because otherwise, people won't be able to understand the urgency, and if they don't understand of the situation, they can't be able to put pressure on people in power, so I think it's a very essential part of this.
GMA: What has surprised you the most about your American tour?
Greta: I don't know, just so many cultural differences. It's very fun to travel to different countries and see how the debate is going there and how much people seem to be aware, and how climate activists work, because they work so different in different parts of the world.
Everything is just so much bigger and so much more than where I come from.
ABC News' Elissa Nuñez contributed to this report.