The ocean floor is turning into a dumping ground. A recent study found that millions of tons of plastic litter the bottom of the world’s oceans and seas. About half of that debris sits in shallow waters near coastlines. And a lot more is expected to settle in the oceans over the coming decades.

The world generates millions of tons of plastic every year—enough to fill a garbage truck every minute. And a lot of it finds its way into the ocean—through runoff, offshore dumping, lost fishing gear, and other sources.

Much of this debris floats on the surface. Some of it forms giant patches, such as the well-known Great Pacific Garbage Patch. Over time, though, a lot of plastic drops into the ocean depths, and much of it settles on the bottom.

To understand how much plastic litters the ocean floor, researchers in Australia poked through the results of many studies. They then developed computer models to analyze those results. Their best model used observations by remotely operated vehicles in the deep ocean.

Their study focused on bits of plastic at least five millimeters across. That accounts for plastic bags, bottles, fishing gear, and other bigger chunks. The model showed that there should be a lot of this debris—somewhere between three million and 12 million tons as of 2020. Almost half of that should be close to shore.

Plastic use is projected to double over the next couple of decades—adding a lot more litter to the ocean floor.

Some strange holes pockmark the bottom of the North Sea. They can be anywhere from a few feet to hundreds of feet wide. But all of them are about four inches deep. That doesn’t match the kinds of pits produced by geological processes or ocean currents. Instead, a recent study says they were created on porpoise.

Scientists have known about the pits for years. The most common explanation said they were produced by blobs of methane bubbling up through the sediments. But such pits are cone shaped. And wider methane pits are also deeper.

To learn more about these odd depressions, researchers studied the floor of the North Sea off the coast of Germany. Using sophisticated sonar, they mapped the sea floor in great detail. They saw more than 40,000 of the pits. And they found that, over a six-month-period, the pits changed. Some of them got bigger, others merged, and new ones took shape.

The scientists also studied ocean currents and marine life in the region. And they found that it’s part of the habitat of the harbor porpoise.

The team suggested that the porpoises scour the shallow pits while they’re hunting for sand eels, which can burrow a few inches into the sediments. The porpoises are known to use their snouts to dig into the soft sand and mud. That poking around may scare the critters out of their hiding places, making them easy prey. And stirring up one sand eel might make others try to get away as well—escaping from pits dug by hungry porpoises.

If you live near the coast, few words are scarier than these: Category Five. That’s the classification for the most powerful hurricanes. The storms have maximum sustained winds of at least 157 miles per hour. And their potential damage is catastrophic. They can flatten houses, bring massive storm surges, and cause heavy rainfall well inland.

In recent years, the most powerful tropical storms have been getting even stronger. And as our planet continues to warm up, they’re expected to get stronger still. So some scientists think it’s time to add even scarier words to the tropical-storm lexicon: Category Six. To qualify for this category, a storm would have wind speeds of at least 192 miles per hour.

A recent study found that five storms would have reached that threshold in the past nine years—four typhoons in the western Pacific Ocean, and one hurricane in the eastern Pacific—Hurricane Patricia. It hit the Pacific coast of Mexico with peak sustained winds of 215 miles per hour—the strongest storm yet recorded.

The study also projected that such monster storms will become more common in the years ahead. Climate change is making the oceans warmer, providing extra “fuel” to power typhoons and hurricanes. That may not increase the number of tropical storms, but it is expected to make the strongest of them even more intense. Some would even qualify for Category Six—a scarier name for the most powerful storms.