The globe\'s marine life is facing a greater risk of large-scale extinctions than at any previous time in human history, marine scientists have warned. An international team of researchers has compared events that triggered massive extinctions of sea life in the past with conditions seen in the seas and oceans globally today, Australia\'s ARC Center of Excellence for Coral Reef Studies reported Tuesday. Global warming and acidification of the oceans, trends seen today, are associated with three of the five largest extinctions of the past 500 million years, the researchers from Australia, the United States, Canada, Germany, Panama, Norway and Britain said in the journal Trends in Ecology and Evolution. \"Currently, the Earth is again in a period of increased extinctions and extinction risks, this time mainly caused by human factors,\" the scientists wrote. \"We wanted to understand what had driven past extinctions of sea life and see how much of those conditions prevailed today,\" co-author John Pandolfi of the ARC Center said. \"It is very useful to look back in time -- because if you forget your history, you\'re liable to repeat it,\" said Pandolfi, an authority on coral reefs and previous mass extinction events. The researchers said they wrote their paper out of concern the oceans appear to be on the brink of another major extinction event. \"In effect, it says we need to stop releasing the CO2 that drives these massive extinction events, curb the polluted and nutrient-rich runoff from the land that is causing ocean \'dead zones,\' manage our fisheries more sustainably and protect their habitat better,\" Pandolfi said.