There are over 400 coastal dead zones around the world, regions so poor in dissolved oxygen that marine life can't survive during the summer months. And it looks like these dead zones will be getting worse in the next few decades — in terms of both size and number.
Dead zones are closely associated with air temperature, which is why they're typically found in the shallow waters in coastal areas. Owing to this connection, scientists are now predicting that climate change will have a significant impact on dead zones around the globe, including the 265 dead zones found along the continental United States.
The NOAA explains the maps:
The map...shows the location of all known dead zones (black and white dots) in the continental United States along with the projected changes in air temperature by the end of the century under a middle-of-the road fossil-fuel-use scenario. Under this scenario, the median global air temperature is projected to be 4.1°F (2.3°C) warmer than the 1980-1999 average.
Of the 265 dead zones in the continental United States, 65 percent (black dots) are projected to experience warming of at least the median 4.1°F by 2099. Globally, that statistic increases to include roughly 94 percent of existing dead zones. The white dots are dead zones where the air temperature is projected to increase by less than 4.1°F
Dead zones happen naturally, but they've also been linked to human activities, such as runoff from farms or sewers. The resulting increases in nitrogen and phosphorus causes an overgrowth of single-celled algae which, after they die, dissolve oxygen during decomposition.
In future, the expanding dead zones are expected to have a detrimental effect on animals such as crabs, mussels, and fish, which require more oxygen to survive in warmer temperatures. The resulting oxygen-poor regions could experience the collapse of entire ecosystems.