Answer:
Over hundreds of years
Step-by-step explanation:
Environmental changes occur as a result of human action and natural processes. These changes leads to the disruption in the normal environmental processes. Examples of human actions include release of pollutants into the atmosphere, overcrowding and destroy of plants and animals habitats etc while the natural causes include earthquakes and the end results include climate changes.
The greatest time frame in which a short-term environmental change can occur is over hundred of years as environmental changes are normally known to occur after several thousands and millions of years.