A recent symposium reviewed the current status and anticipated problems from local warming in the Sierra Nevada. Lake Tahoe has already had a 0.5F temperature increase, which has allowed invasive fish to take hold.
Even if we take radical action now, we are committed to a 2-4F increase in temperature.
The biggest effect (already being felt) is a reduction in snow "stored" at high elevations. This is bad for skiing but really bad for water storage -- if water is not stored as snow, it runs into streams and overwhelms dams. The "more dams" solution is popular, but I am suspicious that they will just be expensive handouts to farmers who should get used to less water. (Cities use 1/4 the water farmers use; they will be fine.)
Bottom Line: Forget global warming, think local warming. We're already in it, and it's time to change some old, bad habits.