A coupled human–environment system (known also as a coupled human and natural system, or CHANS) is an integrated scientific framework for studying the interface and reciprocal interactions that link human (e.g., economic, social) to natural (e.g., hydrologic, atmospheric, biological) sub-systems of the planet. The phrase "coupled human–environment systems" appears in the earlier literature (dating back to 1999) noting that social and natural systems are inseparable. "In 2007 a formal standing program in Dynamics of Coupled Natural and Human Systems was created by the U.S. National Science Foundation." A symposium on "Complexity in Human–Nature Interactions across Landscapes" was held at a 2009 meeting of the U.S. Regional Association of the International Association for Landscape Ecology in Snowbird, Utah. Research into CHANS is increasing in frequency in scientific literature concerning the sustainability and conservation of ecosystems and society.