Climate, environment and sustainability are all intertwined. To find resources, there will be many different avenues of approach.
We will largely ignore the databases in the sciences and engineering: but you will get some -- if not many -- references to scientific works from Web of Knowledge/Web of Science and Scopus, not to mention Google Scholar. I will not mention BIOSIS (Biological Abstracts and Zoological Abstracts), but I will mention Medline/PubMed. I will not list Georef, Engineering Index, Physics Abstracts, or MathSciNet, or Meteorological & Geoastrophysical Abstracts, because your emphasis is on politics, policy and social aspects. Of course the basis for all our knowledge of climate change and its possible mitigation is based on scientific studies and modeling.