This story is part of the pessimistic argument for the future of the planet in our special issue on Earth Day. Read the optimistic argument and the rest of our stories here.

Our nights are getting brighter

Light pollution is now among the most chronic environmental perturbations on Earth. In 2016 scientists estimated that 99 percent of the continental United States and Europe suffer some amount of light pollution.

Their study found that a third of humankind—including nearly 80 percent of North Americans—cannot see the Milky Way. And data from the Suomi NPP satellite suggest that worldwide, light pollution increased by roughly 2 percent a year from 2012 to 2016.

All lights, but especially LEDs, are to blame. Because they’re much more energy-efficient than incandescent and CFL bulbs, LED lights are left on for longer periods, casting cheap light in all directions.

Lack of darkness can affect any animal whose biology depends on circadian rhythms—including us, says Amanda Gormley of the International Dark Sky Association. “We lose a part of ourselves when we lose access to the night sky.” —Nadia Drake

View Images Tourists were the first wave to hit Venice. The sea may be the last—and most destructive. Photograph by MIGUEL MEDINA, AFP via Getty Images

Historic flooding in Venice

Every year, and after almost every rain, the headline is familiar. Venice is flooding and sinking at the same time, which leads to the same wet result: more water filling the 1,200-year-old city’s streets at greater frequency for longer periods. Venice mayor Luigi Brugnaro says the city “will shine again”—but can the island possibly survive a warming world?

The sea level in Venice’s lagoon is four inches higher than it was 50 years ago. The UN’s Intergovernmental Panel on Climate Change expects that so-called hundred-year floods will occur every six years by 2050—and every five months by 2100. One such flood last November left 70 percent of the city submerged.

The more urgent priority may be saving Venice’s treasures and artifacts. After November’s flood, art experts and university students visited damaged museums and churches to move precious objects to higher floors. In some cases, they aimed to find the objects new homes outside of Venice.

That’s only a stopgap until relief arrives from the Italian government’s long-awaited MOSE defense project (also known as the Moses project), which will use giant seawalls to seal off the lagoon. Scheduled for completion in 2011, the project has been delayed by cost overruns and disputes. Officials now expect Moses to start protecting Venice by 2022. —Daniel Stone

View Images Photograph by Joel Sartore, National Geogrphic Photo Ark

Crabs release carbon

Salt marshes store millions of tons of carbon, but burrowing fiddler crabs may be letting it out. Their tunnels create holes in soil that expose carbon-releasing organic matter in Brazil, Tanzania, and China. Researchers say other burrowing animals, like clams and shrimp, may be doing similar damage. —DS

View Images Photograph by GIUSEPPE CACACE, AFP VIA GETTY IMAGES

Allergies are on the rise

If you don’t have springtime allergies, you might soon. And if you already do, they might get worse. The 2018 U.S. National Climate Assessment cautions that allergic illnesses like asthma and hay fever are likely to afflict more people amid climate change. Warmer temperatures and earlier springs combine to spur plants to release more pollen over a longer season to irritate your nose, throat, and eyes. —DS

View Images Photograph by DUNCAN CLARK, NORTHWEST PASSAGE PROJECT, FUNDED BY THE NATIONAL SCIENCE FOUNDATION AND THE HEISING-SIMONS FOUNDATION

In a once unspoiled setting, plastic pollution

Plastics have colonized even Earth’s pristine environments: Researchers found that Arctic sea ice contains more than 10,000 microplastic particles per liter. Polar waters and ice now have the highest concentrations of ocean-based microplastics on the planet, scientists say. And the situation may well worsen, as plastic waste is expected to quadruple in the next 30 years. —DS