Ringed rice coral appears strikingly modest for a species that's caught in the struggle over greenhouse gas emissions.The coral is among the most abundant in Hawaii's waters and is among 82 coral species the federal government is considering listing as endangered or threatened, primarily because growing amounts of carbon in the air and oceans are putting them at risk.The deliberations are fueling a debate about the best way to help coral, given there is not yet a global plan to reduce greenhouse gas emissions.Environmentalists say listing the coral as an endangered species would then require federal agencies to limit actions that would result in greenhouse gases that would harm the coral habitat. They pushed the same argument when polar bears were as a threatened species in 2008.The Obama administration says that while these species may need the special protections that the 37-year-old law affords, the law is not the venue to address greenhouse gas emissions. They say a "comprehensive strategy" developed with Congress is the better way to deal with it.Coral researchers like Kuulei Rodgers of the Hawaii Institute of Marine Biology say action needs to be taken soon.Models created by her lab and other scientists show the world's coral reefs will suffer major declines by 2050 — just four decades from now — if humans don't cut back the amount of carbon they're pumping into the air."The reef will break apart," Rodgers said. "You're going to see more sensitive species of coral disappear completely. You won't see them."The National Marine Fisheries Service began its review for the 82 species last month. Of the total, 75 are in the Pacific including the U.S. territories of American Samoa and Guam. Nine are in Hawaii.Ringed rice coral — which sometimes has a purple hue, other times rust orange or brown — grows in small patches in the nearshore waters of Hanauma Bay, one of Hawaii's most popular nature preserves. It provides food and shelter for large numbers of fish and other marine lifeIt's a candidate for listing because it's only found in the Hawaiian islands. This makes the species vulnerable to being wiped out if there's a heat wave or an invasive species infiltrates its habitat.The agency has about a year to finish the review.In the meantime, neither the U.S. or the international community has determined how it will cut greenhouse gas emissions. Restrictions could take jobs away from coal and oil producing states, and increase costs for businesses, making them politically risky.The U.S. promised the United Nations it would cut its greenhouse gas emissions by 17 percent by 2020. But Congress must approve this plan, something that's not guaranteed.Earlier this month, U.S. President Barack Obama met with 14 senators on the issue, telling them he wanted comprehensive legislation that would cap greenhouse gas emissions.The government has faced the question of how to deal with greenhouse gases threatening the habitats of vulnerable species before. In 2008, the government listed polar bears as a threatened species, saying global warming was causing sea ice, the polar bear's primary habitat, to melt.As traditionally applied, the Endangered Species Act would prompt the government to restrict the actions of state agencies and companies receiving federal permits if their activities were to harm the bear's habitat.This approach has worked successfully for decades, helping prevent the extinction of 98 percent of species classified as endangered.But the Interior Department said it was "not possible" to directly link the greenhouse gas emissions from a specific project — like a power plant — to melting ice floes harming the polar bears. So the department is not seeking to restrict them.J.B. Ruhl, a professor at Florida State University College of Law, said the same logic would apply to the coral if they're listed."How exactly do you get from their molecules of carbon dioxide are the ones that caused what's going on here, but not those other molecules that are coming from farms?" Ruhl said. "Or people driving in New York City? Or people using air conditioning in Tucson? There's no way to sort it out."Rising carbon levels threaten coral many ways.First, greenhouse gases trap energy from the sun, warming the planet. Coral is vulnerable in part because it has trouble surviving in waters just one to two degrees warmer than the hottest temperatures they experience during the summer.When the ocean becomes too hot, the coral expel the algae they normally rely on to survive. This makes them appear "bleached."The oceans are also absorbing some of the carbon humans are pumping into the atmosphere when they drive cars and use electricity generated by burning fossil fuels. The added carbon boosts the acidity of the ocean, making it harder for coral to grow. The acidity also weakens coral skeletons, increasing the likelihood they'll break during storms.Scientists had been predicting the amount of carbon in the ocean would double by 2100, but they now say it could happen by 2050 or earlier.Kassie Siegel, senior counsel at the Center for Biological Diversity, said the government should treat greenhouse gases just as it would other pollutants when it comes to protecting endangered or threatened species."If we keep building coal-fired power plants, we will lose coral reefs," Siegel said. "One way or another we need to look at the impacts and we need to do something about it. And the Endangered Species Act is one way to get there."