They sound like something from a horror movie, but red tides are all too real. They begin with tiny, reddish creatures called dinoflagellates. They're normally harmless. But every now and then, dinoflagellate populations suddenly explode. The red organism is a dinoflagellate. Source: Woods Hole Oceanographic Institution All those red bodies make the water look red too. And that's not all. Some species release a nerve toxin that can harm or kill people who eat shellfish from the same water. click to enlarge image Red tides killed these Florida fish. Source: Woods Hole Oceanographic Institution Scientists don't know exactly what triggers red tides. They generally occur toward the end of summer—when water is warm. So what happens if whole oceans grow hotter?

Many people think of "the beach" mainly as a place to relax. But our coastal areas are much more than that. In ancient times, oceans provided all-you-can-catch food, and boats often were the easiest way to get around.

Fish merchants in 1920 await the latest catches from these ships in Boston Harbor. Source: NOAA: History of Groundfishing

Ports grew into prosperous and mighty cities. Many remain important trade centers today. Fishing and shipping still are huge industries. Two-thirds of Earth's six billion people live in coastal areas—and this number keeps growing.

Source: NOAA: Shoreline Crowding

That means that whether the sea grows hotter—as a result of global warming—isn't just an issue for scientists and environmentalists. It could mean a flood of trouble for everyone.

• Coastal flooding: As glaciers melt, sea level rises. Rising tides could force huge numbers of families from their homes, especially in poorer countries. Even in places with adequate sewer systems, frequent flooding prevents them from functioning well.
• Too much salt: All that salty ocean water could come inland and seep into farmland, river valleys, and groundwater.
  This could poison plants, freshwater fish, and drinking water.
• Disease: Warmer oceans could harbor more disease-carrying microbes,
  which could spread illnesses such as cholera.

Would you want saltwater from your faucets?