Coupled human–environment system
A coupled human–environment system (known also as a coupled human and natural system, or CHANS) characterizes the dynamical two-way interactions between human systems (e.g., economic, social) and natural (e.g., hydrologic, atmospheric, biological, geological) systems. This coupling expresses the idea that the evolution of humans and environmental systems may no longer be treated as individual isolated systems, compared to earlier times in human history when human-environmental interactions were weak and one-way (linear).
As CHANS research is relatively new, it has not yet matured into a coherent field. Some research programs draw from, and build on, the perspectives developed in trans-discplinary fields such as human ecology, ecological anthropology, environmental geography, economics, as well as others. In contrast, other research programs aim to develop a more quantitative theoretic framework focusing on the development of analytical and numerical models, by building on theoretical advances in complex adaptive systems, complexity economics, dynamical systems theory, and the earth sciences. To some extent, all CHANS programs recognize the need to move beyond traditional research methods developed in the social and natural sciences, as these are not sufficient to quantify the highly nonlinear dynamics often present in CHANS. Some research into CHANS emulates the more traditional research programs that tended to separate the social from the ecological sciences.
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.":218 Research into CHANS is increasing in frequency in scientific literature concerning the sustainability and conservation of ecosystems and society.
Funding by the National Science Foundation to study "Dynamics of Coupled Natural and Human Systems" occurred from 2001-2005 as a part of a "special competition" within the "Biocomplexity in the environment" program, and in 2007 gained formal standing. 
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- Environmental Resource and Education Funding Opportunities, National Science Foundation.
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- https://www.nsf.gov/news/priority_areas/biocomplexity/index.jsp[full citation needed]
- https://www.nsf.gov/pubs/2014/nsf14601/nsf14601.htm[full citation needed]
- CHANS-Net is an international network for researchers studying or people interested in the topic of Coupled Human and Natural Systems. The organization facilitates communication and collaboration.
- Biocomplexity in the Environment, a 2006 priority area of the National Science Foundation.