Marine species are under threat from rising levels of acidity in the oceans, says the UK's Royal Society.
Tiny coccolithophorids form vast populations
Unless carbon dioxide emissions are cut, there could be irreversible damage to ecosystems, it warns.
It is further evidence of the need to take action at next week's G8 summit, says working group chair, John Raven.
"Failure to do so may mean that there is no place in the oceans of the future for many of the species and ecosystems that we know today," he said.
The report: Ocean acidification due to increasing atmospheric carbon dioxide, says excess carbon dioxide (CO2) in the atmosphere has already increased the acidity of the world's oceans to a level that is irreversible in our life times.
The world's oceans have already absorbed about half of the CO2 produced by humans, mainly by the burning of fossil fuels, over the past 200 years.
This has led to a reduction of the pH of seawater by 0.1 units on the 14-point scale. If emissions of CO2 continue to rise as predicted, there will be another drop in pH by 0.5 units by 2100, a level that has not existed in the oceans for many millions of years.
"The carbon dioxide dissolving in the ocean is not a trivial problem, the effects are likely to be severe in some areas of the ocean," Prof John Raven told the BBC News website.
"These effects may not be immediately translated into direct economics but there are potentially important effects on the way the earth system is working and how it will continue over many millennia to support humans in the way we've become accustomed."
Scientists fear the rising acidity of seawater will have a particularly detrimental effect on corals and other marine organisms, because it will be harder for them to form their skeletons and shells.
Tiny shelled plankton in the Antarctic Ocean that are a major food source for fish and other animals are likely to be among the first to suffer.
Higher CO2 levels will also make it harder for many marine fish and shellfish to breathe and reproduce.
In addition, the changes in the chemistry of the oceans will reduce their ability to absorb CO2 from the atmosphere, which in turn will accelerate the rate of global warming.
Dr Carol Turley of the Plymouth Marine Laboratory said that ocean acidification is a "sister" problem to that of climate change.
"The oceans have already taken up about 50% of the CO2 that man has produced over the last 200 years and will continue to do so," she said.
"Essentially, the oceans have been reducing the impact of climate change but at their own expense."