All the H2O we have on Earth now is all we will ever have. Water molecules might get polluted with contaminants for a time, or they might get locked up in glaciers for eons, or whole regions may suffer decades of drought, but Earth’s overall water balance never fluctuates. So we’re never going to run out of water. That doesn’t mean we don’t have to worry about supply, both undersupply due to pollution, drought, and water diversion projects or oversupply because of climate change. For example, if all the glaciers were to melt over the course of just a few decades, ocean levels could rise some 230 feet, drowning virtually every coastal city (and many others) on the globe.
The phosphorus cycle functions similarly — the phosphorus atoms the Earth has now are essentially all it will ever have. For billions of years, they leached into the living world as their host rocks eroded, like drops of water off a melting glacier. Now that we have figured out how to turn those drips into a gusher by mining the sedimentary rocks created by dead sea life raining down upon the ocean floor, we are flooding the world with it — in some cases to disastrous effect. Like water, we can’t live without phosphorus but, like water, too much of it causes its own set of drastic problems. Read more…