OSLO, Sept 5 (Reuters) - Global warming is disrupting ocean life from plankton to whales and the heat may linger in the depths for centuries even if man-made greenhouse gas emissions are halted, an international study said on Monday.
Rising temperatures in the seas were also having wider knock-on effects such as by disrupting rainfall patterns over land, spurring extreme weather events and aiding a spread of water-borne diseases, it said.
"Ocean warming may well turn out to be the greatest hidden challenge of our generation," according to a 460-page study by the International Union for Conservation of Nature (IUCN), which includes scientists, governments and activists.
"The impacts are already being felt," it said of the findings by 80 scientists in 12 nations. The oceans have absorbed more than 90 percent of the heat trapped by man-made greenhouse gas emissions since the 1970s, it said.
Warming is driving marine life such as plankton, jellyfish, fish and turtles towards the poles, according to the study released during an IUCN congress in Hawaii.
"The speed of change in the ocean, such as the poleward range shifts in marine systems, is happening between 1.5 and 5 times faster than on land. Such range shifts are potentially irreversible," it said.
Some migrants, such as whales, were arriving at the wrong time to feed in traditional breeding grounds. Some seabirds, such as those nesting on traditional sites in the North Atlantic, were now in the wrong place to catch fish.
And warming would penetrate ever more into the deep ocean, below 700 metres (2,300 ft). "The effects will continue to be experienced there for decades, if not centuries, even if a complete cessation of carbon dioxide emissions were possible," it said.
China and the United States, the top two emitters, said on Saturday that they had ratified a 2015 global deal to combat climate change. The pact aims to phase out emissions in the second half of this century.
Overall, warming would cause a "cocktail of negative effects" in the oceans, despite a few positive impacts, the study said. This year is likely to be the warmest since records began in the 19th century, ahead of 2015.
Among other impacts, coral reefs, vulnerable to a bleaching from global warming, were set to suffer ever more, it said. And sea ice in the Arctic could largely disappear in summers in the next 5 to 15 years. (Reporting By Alister Doyle; Editing by Richard Balmforth)