A U.S. Fish and Wildlife Service study concluded that bear spray is more effective than firearms in stopping bear attacks.
The U.S. Geological Survey (USGS) has authorized its field employees to carry bear spray based on the USFWS report and a study done by Canadian bear biologist Dr. Stephen Herrero that reached similar conclusions
A recent AP story highlights some of the issues arising from the recently enacted federal law that allows firearms in national parks. The concern is that people will now use firearms for bear protection rather than bear spray, resulting in more bear deaths than necessary. A large part of the concern is that people often mistake non-charging bear movement for a bear attack. Using bear spray in such situations would be harmless. Using a firearm might be lethal.
The full AP story can be read here: New law pits guns vs. grizzlies in national parks