1. Because the increase of temperatures.
2. Why they effect humans - Melting glaciers add to rising sea levels, which in turn increases coastal erosion and elevates storm surge as warming air and ocean temperatures create more frequent and intense coastal storms like hurricanes and typhoons.
2. Why they effect the ecosystems - Continual melt from glaciers contributes water to the ecosystem throughout dry months, creating perennial stream habitat and a water source for plants and animals. The cold runoff from glaciers also affects downstream water temperatures.