Scientists at the Carnegie Institution have documented ongoing changes in the high-altitude bands of fast winds that strongly influence the paths of storms and other weather systems. The shifts are possibly in response to global warming.
This, to me, is the most important aspect of global warming (and the reason why I think "global warming" is a misleading name). The weather patterns are changing. The change might not be toward warmer weather at every spot on the face of the Earth or on every day of the year. Much of our construction in coastal areas and river bottoms as well as planning in our global agricultural system is based on assumptions that the near future climate will be similar to the near past climate. When the climate changes unpredictably, we get planning disasters. At the very least harmful end of things are golf course centered retirement communities that will fail if there isn't enough water. At the worst end are crop failures, spiking food costs, and local famines. Billions of dollars will be lost and people will die when we get it wrong.
The fact that there is so much uncertainty and debate about how much or even if the oceans are going to rise, whether or not hurricanes will get stronger or not, and how annual rainfall patterns are going to shift means our ability to plan in any meaningful way is suffering. That is the real danger of global warming.