Climate change is the largest human-caused stressor on the world's oceans, according to a new study published in the journal Nature.
Of the areas observed in the study, about two-thirds of ocean and 77 percent of waters in national exclusive economic zones experienced increased harm from human activity, based on a comparison of data between 2008 and 2013. Almost all of those detrimental effects on marine ecosystems came from climate change, rather than other practices such as fishing, pollution and agricultural runoff.
"The many stressors associated with climate change (anomalously high sea surface temperatures, ocean acidification and increasing ultraviolet radiation) dominate humanity's footprint on the open ocean, but commercial fishing and shipping also cover large areas of the oceans and contribute significantly to overall impact," said the study from researchers at University of California, the Hawaii Institute of Marine Biology, Scripps Institution of Oceanography, the National Oceanic and Atmospheric Administration, Conservation International and Imperial College London.
Climate scientists have warned that oceans are gobbling up carbon emissions, leading to ocean acidification that is killing coral reefs that are valuable habitats for marine life and is imperiling algae that provide oxygen to aquatic ecosystems. Warming waters are forcing some marine life to flee their traditional habitats, affecting commercial fishing operations.
The study tracked 19 types of human-induced stressors across 20 global marine ecosystems. While 66 percent of oceans saw an increase in human impact — largely in tropical, subtropical and coastal regions — just 13 percent saw a decline, the study said. The study said 97.7 percent of ocean is affected by more than one human stressor.
The study noted several "hotspots" in the North Sea and South and East China seas.
"National waters currently experiencing highest estimated impacts include those off Singapore, Jordan, Slovenia and Bosnia, while the most impacted coastal ecoregions include the Faroe Islands, Eastern Caribbean, Cape Verde and Azore islands," the study said.
Coastal population wasn't a significant determinant of ocean stress, the study said. While countries with the greatest increases in coastal population over the five-year period tended to show greater effects on the ocean, absolute population in those regions made no difference on ecosystems. Areas that were fairly uninhabited also showed upticks in ecological strain.
Commercial fishing was not a major cause of damage, either. Impact increased in less than 10 percent of the ocean area and 17 percent of the exclusive economic zones studied, though the study noted overfishing could have long-lasting effects.
"In fact, impacts from four of the five types of commercial fishing decreased in 70–80 percent of the ocean, consistent with results suggesting global catch has stabilized or is declining in most parts of the ocean and that well-managed fisheries are achieving sustainable yields," the study said.