Civilizations live and die by their access to energy. It's critical that the world continues to make energy cheaper and cleaner available. Solar seems to be the obvious choice for accomplishign this.
People choose their method of transportation by weighing convenience and cost of their options. It's unreasonable to think people are going to ride transit for some altruistic values. The only way to reduce traffic is to make efficient transit more compelling than driving.
The US Dollar has had a good run but it's only a matter of time before hyperflation. The tempation to print dollars to postpone an economic depression is too appealing for politicians and the federal reserve. When and what's next are the interesting questions.
Managing water will become an increasing challenge for communities as populations rise, climates change and existing sources dwindle or become polluted.