Water

PAST: 

The river sources were larger, had more aquatic species, rivers and seas had no pollution, most of the water was clean, the poles were larger and controlled the seas. 

PRESENT: 

Water is scarce due to pollution, aquatic species are disappearing, so we're running if natural water resources, the poles are melting from the heat increasing growth of the sea. 

FUTURE:

The water will become scarce to the point of becoming a luxury to have it, rising sea will be even higher, causing tidal waves and floods abysmal, no aquatic life, there will be no poles, the water will not be potable.