Warming oceans are not only spreading diseases among animals, humans and marine lives but also hampering food security in many countries.
A recent study has red-flagged change in weather patterns due to warming of oceans as a phenomenon that does not bode well for major key producing countries, like India. This may well be the "greatest" hidden challenge for the present generation, it adds.
Changes in ocean-focussed atmospheric patterns have direct implications on food production as the yield is impacted. "The consequences for society of changing weather patterns due to the warming of the oceans are considerable," said the report titled "Explaining ocean warming: causes, scale, effects and consequences".
The report, released by the International Union for Conservation of Nature (IUCN), said they involve a mix of food and water factors, and the evolution of various types of risk.
Noting that there have already been changes to precipitation patterns in a number of areas of the planet resulting from large-scale atmospheric teleconnections with ocean warming, the report said there can be increased rainfall in some mid-latitude and monsoon areas and decrease over various sub-tropical regions.
"Both will have impacts on the yields of crops over a range of important food producing areas such as Australia, North America and India," it said.
The report said there were good correlations between wheat and maize yields with the NAO (North Atlantic Oscillation) and PDO (Pacific Decadal Oscillation), so changes in these ocean-focused atmospheric patterns have direct implications on food production.
Similarly, increasing temperatures tend to reduce maize yields, if all other factors are held constant, it said.
"At sea, warming temperatures will cause changes to the abundance and range of marine species used for food, leading to implications for both the billion people who depend on fish for their principal source of protein and the fishing and aquaculture industries linked to this harvesting."
It also warned that the changes in the ocean are happening between 1.5 and 5 times faster than those on land.
"Such range shifts are potentially irreversible, with great impacts on ecosystems. What this will result in, decades down the line, is less clear.
"It is an experiment where, rather than being a casual observer in the lab, we have unwittingly placed ourselves inside the test-tube," it said, adding that ocean warming may well turn out to be the greatest hidden challenge of our generation.
The report, launched at the just concluded IUCN World Conservation Congress held in Hawaii, said more than 93 per cent of the enhanced heating since the 1970s resulting from human activities has been absorbed by the ocean, and data show a sustained and accelerating upward trend in ocean warming.
"The scale of ocean warming depicted in the report is truly staggering: if the same amount of heat that has gone into the top 2 km of the ocean between 1955 and 2010 had instead gone into the lower 10 km of the atmosphere, the Earth would have seen a warming of 36 degree Celsius," says the report compiled for IUCN by 80 scientists in 12 countries.
Major changes caused by ocean warming and other stressors described in the report include impacts on entire ecosystems from polar to tropical regions, predicted to increase further in scale, stretching from accessible coasts to the deep ocean seabed.
The entire groups of species such as plankton, jellyfish, fish, turtles and seabirds could be driven by up to 10 degrees of latitude towards the Earth's poles to keep within reasonable environmental conditions.
It also spoke about loss of breeding grounds for groups such as turtles and seabirds, and impacts on the breeding success of birds and sea mammals; and seasonality shifts by plankton, leading to potential mismatch between plankton species with fish and other marine wildlife.
As the ocean warms the atmosphere above, and beyond, is being affected by it.
"Developing changes in air-sea interactions are being seen around the planet, in many cases leading to enhancement or shifting of extreme weather.
“This can be mid-latitude storminess, linked to changes in Arctic sea-ice, more severe hurricanes or changes to the character of El Ni o events or monsoons, all linked to tropical ocean changes," it said.
These changes to the ocean, and then atmosphere, are set to continue as anthropogenic warming continues this century.
"More and more change to the ocean will occur, in terms of sea ice cover, stratification, the global meridional overturning circulation or the increased melt water runoff and calving of icebergs into the ocean," the report said.
The report also describes the inadequacy of current knowledge, capabilities and capacity to adequately study ocean warming, and to advise and cope with the associated challenges.
(With agency inputs)