In my view, one of the most remarkable statements made in this special issue came in Gleditsch's introduction, where he acknowledged the seeming inability of quantitative studies to deal with complex, interactive social-ecological systems.  Commenting on the lessons that the large-N community could learn from the case study environment-conflict researchers Gleditsch wrote: Kofi Annan (2006: 9–10) argued in one of his last reports as UN Secretary-General, that ‘pollution, population growth and climate change are . . . occurring now and hitting the poorest and most vulnerable hardest. Environmental degradation has the potential to destabilize already conflict-prone regions, especially when compounded by inequitable access or politicization of access to scarce resources.’ Here, he is invoking an interaction effect of climate change with no less than three other variables. Unfortunately, it seems unlikely that case study researchers or large-N scholars will launch a systematic investigation of such complicated interaction patterns any time soon."  

If the large-N researchers are incapable of "systematic investigation" of climate change-security research with four variables, then this is a bankrupt research agenda.  For case study researchers, even four variables seems remarkably restricted.  Future studies have to address this issue more systematically.  What are the barriers to designing more complex research studies with multiple variables?  If climate modelers are using dozens of variables in their models (albeit, with variables of a different level of precision), then why can't it be done in social-ecological research?  Also, is there not some way to bridge the gap between large-N studies and case study approaches – something that has been a constant theme in this field for the past decade?  The findings of these large-N studies need to be ground-truthed, and case study approaches can help to do this, using survey and/or ethnographic approaches. A recent study in the right direction was done by USAID and International Alert – Marisa Goulden and Roger Few, Climate Change, Water and Conflict in the Niger River Basin.We should all applaud the efforts by large-N researchers to lower their analytical focus to the sub-national level.  However, doing so also means accepting the sensible conclusions of the commentators above – that complexity can't be ignored.  In fact, it's probably true that the lower the level of analysis, the greater the requirements that studies are sensitive to complex interactions across scales and between variables.

Of course, statistical studies of the relationship between climate change and conflict do not hesitate to invoke four or more variables in their explanatory models. And as Johno, Andrew, and Frank point out, research on interactions between climate variables and other factors is well under way. However, a full study of all possible interaction effects (two-way. three-way …) between climate variables and three explanatory factors, would be difficult indeed. Studying complexity is important, but it won't help us much if models are constructed to be so complex that they are untestable.

Nils Petter Gleditsch