I agree with those who warn against seeing COP15 as a last chance. My own hackneyed historical analogy of choice relates to a letter sent by Winston Churchill to British officers on 4 July 1940 at a time when German invasion seemed imminent. (I have the copy that was sent to my grandfather, who was Naval Liaison Officer with Army Eastern Command.) It says, basically, don't panic and don't give in. 
Moving beyond historical analogy, Robert Butler at Ashdenizen notes this from Steve Waters:
Climate change seems to elude dramatisation, perhaps because it presents not only a challenge to the habits of everyday life, it challenges the habituated imagination itself, it challenges the very basis of story-telling.Footnote
 (added 1 Dec) James Hansen expresses this in terms relevant today here and here.