Maine’s largest environmental advocacy organization is seeking volunteers for its fifth annual cold-water ocean plunge, to raise money in the name of global warming. The Natural Resources Council of Maine said its Polar Bear Plunge will be held at noon on Dec. 31 at Portland’s East End Beach. The event raises money and awareness for the group’s work on climate-change issues. Those not up for a bone-numbing dip into the ocean can still raise money and take part in a 5-kilometer walk or run. Last year nearly 200 people took part, raising $18,000.