NEW YORK: The world's fisheries will be, on average, 20 per cent less productive in the year 2300, according to a study.This bleak future will be characterised by 9.6 degrees Celsius increase in mean surface air temperature, nearly 10 times the warming we have seen to this point.The extended climate warming will drastically alter wind patterns, boost ocean surface temperatures and melt nearly all the sea ice in polar regions."These conditions will cause changes in phytoplankton growth and ocean circulation around Antarctica , with the net effect of transferring nutrients from the upper ocean to the deep ocean," said J Keith Moore from the University of California, Irvine in the US."Marine ecosystems everywhere to the north will be increasingly starved for nutrients, leading to less primary production (photosynthesis) by phytoplankton, which form the base of ocean food chains," Moore said.The researchers used an empirical model linking plankton growth to present-day fish catches and then factored in dwindling nutrients and plankton populations due to climate warming in the coming centuries."By looking at the decline in fish food over time, we can estimate how much our total potential fisheries catch could be reduced," said Moore.Months of computations using thousands of central processing units were needed to simulate the climate and oceans up to 2300.According to the findings, published in the journal Science, fisheries in the North Atlantic will be down nearly 60 per cent and those in much of the western Pacific will experience declines of more than 50 per cent in the year 2300."The climate is warming rapidly now, but in the ocean, most of that added heat is still right at the surface. It takes centuries for that heat to work its way into the deeper ocean, changing the circulation and removing the sea ice, which is a big part of this process," Moore said."This is what's going to happen if we don't put the brakes on global warming, and it's pretty catastrophic for the oceans," he added.