A view of major bleaching on the coral reefs of the Society Islands on May 9, 2019 in Moorea, French Polynesia. GETTY IMAGES



Temperatures are rising both on land and at sea, with climate experts ringing alarm bells about unprecedented sea surface temperatures in the North Atlantic.



With El Niño's return, warmer than average temperatures are expected to persist, and could impact sea ice levels, fisheries and coral.



"We are in uncharted territory and we can expect more records to fall as El Niño develops further and these impacts will extend into 2024," World Meteorological Organization director of climate services Christopher Hewitt said Monday. "This is worrying news for the planet."



The National Oceanic and Atmospheric Administration in late June warned that half of the world's oceans may experience marine heat wave conditions by September. Research scientist Dillon Amaya said that in the organization's Physical Sciences Laboratory's decades of measurement, such widespread high temperatures had never been seen.



"Normally, we might expect only about 10% of the world's oceans to be 'hot enough' to be considered a marine heatwave, so it's remarkable to reach 40% or 50%, even with long-term warming," Amaya said.



Global sea temperatures in May and June were at record highs for the time of year. The temperatures also "much higher than anything the models predicted," Dr. Michael Sparrow, head of the World Meteorological Organization's world climate research department, said.



Those high temperatures came, in part, before El Niño — which is associated with high ocean temperatures — even began, the European Union's Copernicus Climate Change Service stressed in a July report.



With warmer temperatures, Antarctic sea ice "reached its lowest extent for June since satellite observations began, at 17% below average, breaking the previous June record by a substantial margin," according to Copernicus. The region is usually thought of as being relatively stable when compared to the Arctic, Sparrow said.



High ocean temperatures are also causing coral bleaching, which can leave coral vulnerable to deadly diseases, experts warned. NOAA calls coral bleaching "one of the most visible and damaging marine ecological impacts of persistently rising ocean temperatures." Coral-based ecosystems act as nurseries for fish.



Spiking ocean temperatures can also impact fisheries. As water temperatures rise, marine life is moving toward the poles to stay cool, according to NOAA. This can mean fish are moving out of the range of fishers. Marine fisheries and seafood industries in the U.S. supported around 1.7 million jobs and $253 billion in sales in 2020, according to the agency.



Warmer ocean water can kill fish because it holds less oxygen than cooler water. In June, thousands of dead fish washed up along the Texas Gulf Coast because of a "low dissolved oxygen event."



Marine heat waves can also produce "hot spots" of harmful algae, which produces a toxin, domoic acid, that can accumulate in shellfish and make it dangerous to eat, according to NOAA.



Around 90% of global warming is occurring in the ocean, according to NASA. Scientists attribute the widespread heat of the global ocean waters to human-caused climate change.



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