U.S. government scientists say global warming is causing an alarming increase of acid in the world's oceans, a trend that ultimately threatens the seas' delicate ecosystems.

In a report released Wednesday, scientists used a scale, commonly referred to as "pH," that measures the levels of acid within a given substance. A low pH number signifies a high concentration of acid.

The report says the oceans' pH level has dropped one-tenth of one percent (8.2 to 8.1) since 1800, and is expected to fall even lower to 7.9 by the year 2050.

Scientists say the rise of acidic levels will eventually weaken and ultimately kill the oceans' colorful coral reefs, which rely on calcium in seawater to build their shells and skeletons.

Scientists say an increase in the use of fossil fuels has led to a rise in the levels of carbon dioxide that are trapped in the Earth's atmosphere, causing a so-called "greenhouse gas" effect that increases the planet's temperatures.

Global warming has been blamed for such environmental changes as the melting of polar ice and stronger tropical storms.

Some information for this report was provided by AP.