WASHINGTON (AP) -- While carbon dioxide has been getting lots of publicity in climate change, reactive forms of nitrogen are also building up in the environment, scientists warn.

"The public does not yet know much about nitrogen, but in many ways it is as big an issue as carbon, and due to the interactions of nitrogen and carbon, makes the challenge of providing food and energy to the world's peoples without harming the global environment a tremendous challenge," University of Virginia environmental sciences professor James Galloway said in a statement.

"We are accumulating reactive nitrogen in the environment at alarming rates, and this may prove to be as serious as putting carbon dioxide in the atmosphere," said Galloway, author of a paper and co-author of a second on the topic in Friday's issue of the journal Science.

While nitrogen alone is inert and harmless, reactive nitrogen compounds - such as ammonia - have been released by its use in nitrogen-based fertilizers and the large-scale burning of fossil fuels.

Various forms of nitrogen contribute to greenhouse warming, smog, haze, acid rain dead zones with little or no life along the coasts, and depletion of the ozone layer in the stratosphere, the researchers concluded.

The researchers propose ways to reduce nitrogen use, ranging from encouraging its uptake by plants to recovering and reusing nitrogen from manure and sewage and decreasing nitrogen emissions from fossil fuel combustion.