Ocean levels have risen several inches over the last century, and that's only likely to increase going forward. Most of that is related to climate change — but now scientists may have discovered a hidden factor in all this: irrigation.
At first glance, that might seem surprising. After all, irrigation is just moving water from one area to another, to allow people to live in naturally dry or arid areas. The problem is that not all irrigation comes from water already on the surface - a lot of it is now extracted from deep underground, introducing tons of extra water that would not otherwise be a part of the planet's water cycle.
Researchers from the US Geological Survey calculated that the last century saw over a thousand cubic miles worth of water extracted from underground and used for irrigation purposes. That was enough water to boost ocean levels by about half an inch, accounting for 12.6% of the total sea level rise in the 20th century.
And all this isn't likely to stop anytime soon. Ground water extraction has skyrocketed in the last decade, with some estimates say we're now bringing up about 34 cubic miles each year. That's enough to increase sea levels by .016 inches each year, which is 13% of the current rise. While melting ice and other climate-related factors remain responsible for the vast majority of the sea level increase, this adds a new wrinkle to how we use irrigation and ground water going forward.