Which kind of environmental change would a tornado be? short-term, because it occurs very quickly
long-term, because it lasts a long time
short-term, because it affects only a small area
long-term, because they have been happening for millions of years

As i see it, it could be short-term because it occurs very quickly. A tornado usually lasts 2-3 and maximum 10 minutes. If you say its long-term because they have been happening for millions of years now that is a different point of view. I think it wouldn’t be a long-term environmental change because tornadoes have been happening for millions of years.
So my final answer to your question is, its SHORT-TERM BC IT OCCURS VERY QUICKLY. (Its another thing if you ask what kind of environmental change would tornadoes CAUSE)