You won't find it in your kitchen or bathroom: Carbon sinks are natural systems that suck up and store carbon dioxide from the atmosphere.

The main natural carbon sinks are plants, the ocean and soil. Plants grab carbon dioxide from the atmosphere to use in photosynthesis; some of this carbon is transferred to soil as plants die and decompose. The oceans are a major carbon storage system for carbon dioxide. Marine animals also take up the gas for photosynthesis, while some carbon dioxide simply dissolves in the seawater.

"Combined, the Earth's land and ocean sinks absorb about half of all carbon dioxide emissions from human activities," said Paul Fraser of the Commonwealth Scientific and Industrial Research Organization.

But these sinks, critical in the effort to soak up some of our greenhouse gas emissions, may be stopping up, thanks to deforestation, and human-induced weather changes that are causing the oceanic carbon dioxide "sponge" to weaken, a new study led by Fraser and detailed in the  May 18 issue of the journal Science found.

Scientists are looking for ways to help nature along by devising ways to artificially sequester, or store, carbon dioxide underground.

- Andrea Thompson.