Underground reservoirs affect Earth's balance. Geophysicist Ki-Weon Seo has discovered that we have extracted so much underground water that the tilt of Earth's axis has changed. This has caused the North Pole to move. It is drifting by more than four centimetres a year. Professor Seo calculated that we used more than two trillion tons of groundwater between 1993 and 2010. This caused Earth to wobble.

Groundwater affects Earth's gravity. Seo said: "Every mass moving around on the surface of the Earth can change the rotation axis." Scientists previously thought water-driven shifts were caused by melting glaciers. Seo was puzzled at how this alone could cause a tilt. He concluded that underground water was also a factor. Most groundwater we use is for irrigation. Another researcher said: "The very way the planet wobbles is impacted by our activities."