SNIP takes into account citation practices in the field of interest. A journal's field is the journals citing that journal and the average length of reference lists in papers in that field are taken into account. Also taken into account is the number of those references in the reference lists that are in the database. This defines the "citation potential". This potential is measured relative to the median paper in the dataset which is assigned a potential of 1.0. The ratio of the citations per paper of a journal and its citation potential is its SNIP. This is supposed to allow comparison of citation impact factors across different academic fields. SNIP analyses citations in a given year to articles published in the three previous years (The ISI impact factor uses citations in either the previous 2 or 5 years).
So here are some SNIP scores over the last decade for several environmental and energy economics journals:
I dropped the 2010 SNIP figures as these are all very strange. These are not so different to ISI's impact factors. In particular, we can see the rise in the absolute and relative ranking of the energy journals: Energy Journal, Energy Economics, and Energy Policy. Also JEEM is the top environmental economics journal with Ecological Economics ranked second.
SJR is an eigenfactor type indicator similar in principle to the article influence score produced by eigenfactor.org using the ISI database. I found that these indicators were very volatile on a year to year basis for most of the journals in the sample above and so I'm not sure how useful they are.
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