  In the current UK Research Excellence Framework (REF) and the Excellence in
Research for Australia (ERA) societal impact measurements are inherent parts of
the national evaluation systems. In this study, we deal with a relatively new
form of societal impact measurements. Recently, Altmetric - a start-up
providing publication level metrics - started to make data for publications
available which have been mentioned in policy documents. We regard this data
source as an interesting possibility to specifically measure the (societal)
impact of research. Using a comprehensive dataset with publications on climate
change as an example, we study the usefulness of the new data source for impact
measurement. Only 1.2% (n=2,341) out of 191,276 publications on climate change
in the dataset have at least one policy mention. We further reveal that papers
published in Nature and Science as well as from the areas "Earth and related
environmental sciences" and "Social and economic geography" are especially
relevant in the policy context. Given the low coverage of the climate change
literature in policy documents, this study can be only a first attempt to study
this new source of altmetric data. Further empirical studies are necessary in
upcoming years, because mentions in policy documents are of special interest in
the use of altmetric data for measuring target-oriented the broader impact of
research.
