The declaration is based on results from a UNESCO symposium, The Ocean in a High-CO2 World, held at the Oceanography Museum in Monaco last October.
Prince Albert II of Monaco today urged political leaders to take notice of the declaration ahead of negotiations at the UN Climate Change Conference in Copenhagen at the end of the year.
"I strongly support this declaration," said the prince, whose environmental foundation provided support for the symposium. "I hope the declaration will be heard by all the political leaders meeting in Copenhagen in December 2009."
"The chemistry is so fundamental and changes so rapid and severe that impacts on organisms appear unavoidable," said symposium chair James Orr of the Monaco-based UN Marine Environment Laboratories, a division of the the International Atomic Energy Agency.
"The questions are now how bad will it be and how soon will it happen," said Orr.
The international community has been developing a global observing system for ocean carbon, using ships, buoys, and satellites to understand how the ocean absorbs atmospheric CO2.
The ocean absorbs a quarter of the carbon dioxide emitted into the atmosphere from human activities. Observations from the last 25 years show increasing acidity in surface seawater, following trends in increasing atmospheric CO2.
"Measured recent increases in ocean acidity follow exactly what is expected from basic chemistry; meanwhile, key ocean regions reveal decreases in shell weights and corals that are less able to build skeletal material," said Orr.
"The report from the symposium summarizes the state of the science and priorities for future research, while the Monaco Declaration implores political leaders to launch urgent actions to limit the source of the problem," he said.
"The Monaco Declaration is a clear statement from this expert group of marine scientists that ocean acidification is happening fast and highlights the critical importance of documenting associated changes to marine life," says Professor Sybil Seitzinger, executive director of the International Geosphere-Biosphere Programme, one of the sponsors of the symposium.
Other symposium sponsors were UNESCO's Intergovernmental Oceanographic Commission, the Scientific Committee on Oceanic Research, and the International Atomic Energy Agency.
The other great oceanic consequence of high atmospheric CO2 concentrations from fossil fuel burning - the expansion of low oxygen dead zones - was highlighted in a report Monday from a team of Danish scientists.
Dead zones across the world's oceans would expand by a factor of 10 or more if global warming continues unchecked, the Danish team warned, based on newly developed climate models that project 100,000 years into the future.
"Such expansion would lead to increased frequency and severity of fish and shellfish mortality events, for example off the west coasts of the continents like off Oregon and Chile," said Professor Gary Shaffer of the University of Copenhagen, leader of the research team at the Danish Center for Earth System Science, with scientists from the Danish Meteorological Institute and the National Space Institute.
"If, as in many climate model simulations, the overturning circulation of the ocean would greatly weaken in response to global warming," explained Shaffer, "these oxygen minimum zones would expand much more still and invade the deep ocean."
Extreme events of ocean oxygen depletion are believed to have contributed to some of the large extinction events in Earth history, including the largest such event 250 million years ago, when 96 percent of all marine species and 70 percent of terrestrial vertebrate species went extinct.