In a landmark ruling on Monday, an appeals court said federal authorities may list species as "threatened" based on climate change projections—a "huge victory" for animals that "shows the vital importance of the Endangered Species Act," environmental advocates said.

Big Oil and the state of Alaska had challenged a decision by the National Marine Fisheries Services to list a subspecies of seal as endangered due to eventual Arctic sea ice loss, arguing that the move was speculative, but the Ninth Circuit Court of Appeals decided that the agency had acted reasonably in doing so.

The decision, which overturns a 2014 ruling by a lower court, means federal agencies would be allowed to use climate change projections to protect a variety of wildlife that are likely to be affected by habitat loss and other environmental impacts in the coming decades.

"This is a huge victory for bearded seals and shows the vital importance of the Endangered Species Act in protecting species threatened by climate change," said Kristen Monsell, an attorney for the Center for Biological Diversity who argued the case. "This decision will give bearded seals a fighting chance while we work to reduce the greenhouse gas emissions melting their sea-ice habitat and keep dirty fossil fuels in the ground."

CBD noted that the seals' winter ice habitat is expected to decline 40 percent by 2050 and that the animals also face other threats from proposed offshore oil and gas projects in the waters near Alaska.

"Bearded seals have a shot at survival thanks to the powerful protections of the Endangered Species Act, but only if we take swift and meaningful action to address climate change," Monsell said. "If we don't, amazing creatures like these whiskered ice seals and other animals living in the Arctic could be doomed to extinction."

In listing the species as threatened, the court ruled, the wildlife service "adopted the position of the overwhelming majority of the world's climate scientists."

In the court's statement, Judge Richard A. Paez noted that the Endangered Species Act does not stipulate a species can be listed "only if the underlying research is ironclad and absolute. It simply requires the agency to consider the best and most reliable scientific and commercial data and to identify the limits of that data when making a listing determination."

"The service need not wait until a species' habitat is destroyed to determine that habitat loss may facilitate extinction," he wrote.