Okay kiddo, so basically a climate ensemble is like having a bunch of different climate predictions. Imagine you and your friends are trying to guess what the weather will be like tomorrow. You all have different ideas - one friend thinks it will be sunny, another thinks it will be rainy, and another thinks it will be really windy.
A climate ensemble is kind of like that, but instead of just a few guesses, scientists use computer models to create lots and lots of predictions about what the climate might be like in the future. They do this because predicting the climate is really hard - there are so many factors that can influence it, like the amount of carbon dioxide in the air or how much the oceans are warming up.
By making lots of different predictions, scientists can get a better idea of what the range of possible outcomes might be, and how likely each one is. It's kind of like having lots of different guesses from your friends - while each one might not be exactly right, looking at all of them together can help you figure out what's most likely to happen.
Overall, a climate ensemble is a way for scientists to make better predictions about what the Earth's climate might look like in the future using lots of different computer models.