U.S. scientists say worldwide emissions of carbon dioxide from fossil fuel burning are altering ocean chemistry and threatening marine life. The landmark report released Wednesday by the National Center for Atmospheric Research in Boulder, Colo., summarizes the known effects of increased atmospheric carbon dioxide on marine organisms.

"It is clear that seawater chemistry will change in coming decades and centuries in ways that will dramatically alter marine life," said Joan Kleypas, the report's lead author. "But we are only beginning to understand the complex interactions between large-scale chemistry changes and marine ecology. It is vital to develop research strategies to better understand the long-term vulnerabilities of sensitive marine organisms to these changes."

The report warns that oceans worldwide absorbed approximately 118 billion metric tons of carbon between 1800 and 1994, making them less alkaline and more acidic.

That increased acidity lowers the concentration of carbonate ion, a building block of the calcium carbonate that many marine organisms use to grow their skeletons and to create coral reef structures.

"This is leading to the most dramatic changes in marine chemistry in at least the past 650,000 years," said oceanographer Richard Feely.