It’s as simple as sediment flux: what we’ve moved from land into the water. In 1855 the levees broke along the Yellow River. Now it’s eighty feet above the floodplain. As much earth and stone as used to make the Great Wall of China has been displaced for Hong Kong Island Airport. Think about the movement of water around the earth. Let’s cover the basics: deforestation, fallow lands, tilling, terracing, irrigation systems, subsurface water extraction, mining, transportation systems, waterway re-plumbing, reservoir interception, groynes, jetties, seawalls, breakwaters, harbours, warfare that magnifies many of the above for a duration that extends beyond the period of combat, dissipation in the frozen north. I’m afraid it’s too soon to tell the impact of sea-floor trawling on the continental shelf.