According to this WUWT article, if I'm reading it correctly, life expectancy has risen significantly during the fossil fuel era. If we were to curtail fossil fuel use abruptly, would life expectancy return to previously established rates? If what the article states is true statistically then I can't see people willing to trade a healthier environment for a shorter lifespan. I find it difficult to believe that fossil fuel proponents aren't preaching this stuff, so I tend to think the article is misleading, but I've been wrong before. My guess is that if it ever came to be where global warming threatened the very existence of the human species then trading for a shorter life span is better than having no life at all.
Edit: In case you were wondering about cooking, heating or lighting your house by burning wood. Might have some relevance to the opening paragraph.