"In 2009, the scientific literature caught up with what top climate scientists have been saying privately for a few years now: Many of the predicted impacts of human-caused climate change are occurring much faster than anybody expected — particularly ice melt, everywhere you look on the planet. If we stay anywhere near our current emissions path, we are facing incalculable catastrophes by century’s end, including rapid sea level rise, massive wildfires, widespread Dust-Bowlification, large oceanic dead zones, and 9F warming — much of which could be all but irreversible for centuries. And that’s not the worst-case scenario! The consequences for human health and well being would be extreme."
The following article in the same blog is also the best summary I've found regarding the specific impacts of climate change we can expect, especially if little or no action is taken: http://climateprogress.org/2009/03/22/an-introduction-to-global-warming-impacts-hell-and-high-water/
The author, Dr. Joseph Romm is a physicist and Fellow of the American Association for the Advancement of Science. His blog is one of the best sources for climate change information.