Ocean dead zones multiplying.

The number of oxygen-starved areas in oceans and bays around the world has doubled to 146 since 1990, according to Global Environmental Outlook Yearbook 2003, newly released by the United Nations Environment Programme (UNEP). Such areas have increased every decade since the 1970s.

These ocean areas, often called "dead zones" because they are so inhospitable to most forms of life, occur when high concentrations of nitrogen build up in marine waters. Several types of pollution--including excess chemical fertilizers, human waste, airborne industrial waste, and traffic fumes--can cause nitrogen concentrations to reach damaging levels. The excess nitrogen sparks rapid growth of microscopic plants called phytoplankton. The growth and decomposition of the phytoplankton can use up much of the oxygen in the water and drive out other marine life. Dead zones range up to 70,000 square kilometers in size, an area larger than Latvia.

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Scientists believe that global warming will only exacerbate the problem, via rising seawater temperatures and increased flooding. After the severe Mississippi River flood of 1993, the U.S. National Ocean Service reported that the oxygen-starved area in the Gulf of Mexico more than doubled in size to 18,000 square kilometers.

The dead zones pose a huge threat to fishermen and others who depend on marine resources for their livelihood, a linkage noted by UNEP Executive Director Klaus Toepfer: "Reducing the impacts of agriculture, human wastes, and air pollution on the oceans and seas will be a key component in helping us to meet the Millennium Development Goals and the World Summit on Sustainable Development's Plan of Implementation goals in areas ranging from fisheries and biodiversity loss to sanitation and poverty."

Several countries and regions have already begun to take steps to limit the pollution that creates and aggravates dead zones. Near the River Rhine in Europe, where several countries have agreed to halve the levels of nitrogen they discharge, the quantities of nitrogen entering the North Sea have been reduced by 37 percent. Waste treatment facilities in Europe and North America are using new technologies to reduce agricultural runoff.