Climate change is happening and it means that the Earth is getting warmer because of things people are doing, like burning trees, oil, and gas. But some people don't believe that it's happening! They think the Earth is just doing what it's always done and getting warmer and colder on its own. This is called climate change denial.
It's like if your parents told you that you had to clean your room before you could go play outside, but you didn't want to clean. If you just ignore them and keep playing, you're denying that you have to clean! The people who deny climate change are ignoring the evidence that says it's happening and they don't want to do anything to fix it, like using renewable energy instead of fossil fuels.
It's like sticking your head in the sand instead of facing the truth. This won't help make the problem go away. The more people deny climate change, the worse it will get and the harder it will be to fix. So it's important that everyone works together to understand and fix the problem.