Research for discursive essays can be found through websites, books and articles. Be sure to avoid using sources which are not academic (Wikipedia, etc). A good example of research for a discursive essay on the environment and global warming would be the Met Office (metoffice.gov.uk); an excellent place to find statistics on climate change and backround information on the effects of climate change in the UK. Moreover, BBC Russian Service is a great source for events happening in Russia and its local environmental occurences.