Global warming is likely playing a bigger role than thought in dead zones in oceans, lakes and rivers around the world, according to a new study. Dead zones occur when fertilizer runoff clogs waterways with nutrients, such as nitrogen and phosphorous. The resulting explosion of microbes leaves the water depleted of oxygen. The study, published Monday in the journal Global Change Biology by Smithsonian Institution researchers, found about two dozen different ways — biologically, chemically and physically — that climate change worsens the oxygen depletion.

The researchers looked at 476 dead zones worldwide — 264 in the U.S. They found that computer climate models predict that, on average, the surface temperature around those dead zones will increase by about 4 degrees Fahrenheit (slightly more than 2 degrees Celsius) from the 1980s and 1990s to the end of this century. The largest predicted warming is nearly 7 degrees (almost 4 degrees Celsius) where the St. Lawrence River dumps into the ocean in Canada. The most prominent U.S. dead zones, the Gulf of Mexico and the Chesapeake Bay, are projected to warm 4 degrees (2.3 degrees Celsius) and nearly 5 degrees (2.7 degrees Celsius) respectively.

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Dead Zones worsened by climate change, says Smithsonian study that looked at > 400 dead zones http://t.co/gmEVavLlVv pic.twitter.com/MQoR28xR6m — seth borenstein (@borenbears) November 10, 2014

— The Associated Press