Initial Publication Date: April 1, 2010

Understanding Interactions of Human and Natural Systems

Noelle E. Selin, Massachusetts Institute of Technology

My main interest in researching, teaching and learning about complex systems is in the interactions of human and natural systems. I am interested in how to analyze and model complex human-natural interactions in ways that are useful for decision-making and promote sustainability.

My area of expertise is in atmospheric chemistry modeling. In particular, I look at human-caused air pollution, and use complex models to identify sources and chemical mechanisms that are relevant to air pollution decision-making.

An example of my research in this area is on the transport and fate of mercury in the environment (Selin, 2009). Mercury is a global environmental pollutant, and in the form of the neurotoxin methylmercury, it accumulates in fish and poses a risk to human health, particularly to the offspring of pregnant women who are exposed. Human activities have increased the amount of mercury depositing to the Earth's surface by a factor of three to five. Understanding the pathways by which mercury from natural sources (e.g. volcanic activity), anthropogenic sources (e.g. coal-fired power plants), and the continuing circulation of mercury from both these sources, travels through the environment and reaches humans through exposure is necessary for those who want to minimize or manage these risks.

One policy-relevant question that demands understanding of this complex system is deciding what regulations are appropriate for mercury on what level of political scale (local, national, international). Mercury released in elemental form circulates globally, while that released in oxidized or particulate form tends to deposit on a regional scale. Through global atmospheric chemistry modeling (Selin et al., 2007, 2008), we were able to show that different areas of the U.S. are influenced by different source regions: the Midwest receives up to 60% of its deposition from U.S. sources, but the Southeast (which has the highest measured wet deposition in the U.S.) receives only a small fraction from domestic sources and most from the global background (Selin and Jacob, 2008). This means that addressing the mercury problem will require action at both domestic and international scales (Selin and Selin, 2006). In addition, human systems combine with natural systems through fish consumption patterns to influence exposure. Combining atmospheric models with ecosystem modeling and exposure assessment shows that while domestic action can have a substantial influence on exposure levels for certain U.S. populations (for example, Native American fish consumers in the Northeast/Midwest), the lag times in the biogeochemical cycle of mercury suggest dramatic, global action would be necessary to change the trajectory of exposure from marine fish consumption (Selin et al., 2010).

One of the challenges that I am particularly interested in, both in communicating my research with policy-makers and teaching students interested in applied environmental issues, is how quantitative information and modeling is used (or not used) for decision-making. Understanding the complexities of the natural system is only the first step: a more complicated question is how this natural system interacts with human factors as well as human decision-making. My background is interdisciplinary, and I have previously conducted research on trying to understand how scientific information influences international negotiations (Selin, 2005; Selin, 2006). A particular challenge I have encountered is conveying to students the complexities of using scientific information in political contexts. Students (and scientists in general who become involved in policy) can be overly optimistic about the influence of information; overly pessimistic about providing information (why bother?); or seek a clear, scientific answer to these complex social challenges. I feel that understanding the human-natural interactions, including decision-making under uncertainty, are research questions which require interdisciplinary techniques to address, and I hope to encourage students to pursue these challenges.


N.E. Selin, E. M. Sunderland, C. D. Knightes, and R. P. Mason. 2010. "Sources of mercury exposure for U.S. seafood consumers: Implications for policy." Environmental Health Perspectives, 118(1):137-143, doi:10.1289/ehp.090081122.

N.E. Selin, "Global Biogeochemical Cycling of Mercury: A Review." 2009. Annual Review of Environment and Resources, 34:43-63, doi:10.1146/annurev.environ.051308.084314.

N.E. Selin and D.J. Jacob. 2008. "Seasonal and spatial patterns of mercury wet deposition in the United States: Constraints on the contribution from North American anthropogenic sources" Atmospheric Environment, 42, 5193-5204, doi:10.1016/j.atmosenv.2008.02.069.

N.E. Selin, D.J. Jacob, R.M. Yantosca, S. Strode, L. Jaeglé, and E.M. Sunderland. 2008. "Global 3-D land-ocean-atmosphere model for mercury: present-day versus pre-industrial cycles and anthropogenic enrichment factors for deposition," Global Biogeochemical Cycles, 22, GB2011, doi:10.1029/2007GB003040.

N.E. Selin, D.J. Jacob, R.J. Park, R.M. Yantosca, S. Strode, L. Jaeglé and D. Jaffe, 2007. "Chemical cycling and deposition of atmospheric mercury: Global constraints from observations." Journal of Geophysical Research-Atmopsheres, 112, D02308, doi:10.1029/2006JD007450.

N.E. Selin and H. Selin. 2006. "Global Politics of Mercury Pollution: The Need for a Multi-Scale Approach." Review of European Community and International Environmental Law 15(3):258-269

N.E. Selin. 2006. "From Regional to Global Information: Assessment of Persistent Organic Pollutants (POPs)." Book chapter in: Ronald B. Mitchell, William C. Clark, David W. Cash, and Frank Alcock, eds. Global Environmental Assessments: Information, Institutions, and Influence. Cambridge, MA: MIT Press.

N.E. Selin. 2005. "Applying Assessment Lessons to New Challenges: Sulfur and POPs." Book chapter in: Alex Farrell and Jill Jäger, eds. Assessments of Regional and Global Environmental Risks: Designing Processes for the Effective Use of Science in Decisionmaking. Washington, DC: Resources for the Future.