According to me natural disasters are a result of human greed. The BP oil spill in the Gulf of Mexico caused a disaster to nature along the Gulf Coast of Louisiana to Florida. The oil in the water killed fish, birds, reptiles, and many other species of animals and plants. All because BP upper management wanted to save a buck and hurry using sea water instead of drilling mud.
I do not think that human beings are the only cause for natural disasters. Most natural disasters happen, naturally. They occur naturally in nature. If humans weren't here, there would still be earthquakes and tornados and other natural disasters. Humans do have an impact on some disasters though, but I think it is a small impact in comparison to the big picture.
There is no reason to believe that humans cause natural disasters. Due to climate change, some people have theorized that some natural disasters (like hurricanes and tornadoes) are getting worse because of the harm that has been done to the plant. However, natural disasters cover far more, including volcanoes and earthquakes.