There's numerous natural events that affect the environment, and they can be with bigger or lesser impact compared to how much the humans affect the environment, depending on the intensity and which type of natural event we are talking about.
Some of the natural events that affect the environment are the volcanic activity and the plate tectonics.
The volcanic activity can have global effect, regional one, or only local one, depending on the activity. If there's a large scale volcanic activity across the globe by numerous large volcanoes, than the impact on the environment will huge, not comparable to anything the humans have caused so far.
The plate tectonics are a very slow process, but they have a global impact. If lets say the continental plates start moving and eventually are all positioned around the two poles, that will have a huge impact on the environment, as most, if not all of the land masses will be covered in ice and have very low and extreme temperatures, which is also something that the human activities can not compare to.
