Feedback loop is basically the part of the system, which some portions of the system is outputed and is used in input for a future type behavior. Most times a feedback loop can have 4 stages.
An example of a positive feedback loop is the ripening of a fruit. hope this helps :)
If the water to rise then that could wipe out things like Florida which is only 10 feet above sea level and the population could go down depending on how high the water rose