Writing whine

So, I'm trying to organize the plot for my next writing project, and the stupid bits of scenes won't coalesce into a story. Am v. frustrated. I know the ending, and I know the major scenes, and I have a handful of possible starting points. I just can't get them to make a story. They want to be odd lumps of ideas.

The worldbuilding aspect is giving me trouble because 1)I can't decide on a climate for the setting. I'm torn between hot and scruby Greece/Turkey, and cold and arid Pacific-side South America, and 2)It's AU, and I'm having difficulties getting the social aspects I want in the story to line up with how people might actually behave within those limitations. Grr. Practical thinking.