For years, the federal government has warned that the effects of climate change could pose serious threats to national security — saying rising water levels will eventually hinder military bases.Now, Pentagon officials are taking a more urgent tone, warning that the changing climate poses an "immediate threat" to national security.A new report released by the Defense Department describes climate change as a "threat multiplier" that "has the potential to exacerbate many of the challenges we are dealing with today."Rising temperatures, climbing sea levels, and more extreme weather events...