Systems designed to remove carbon dioxide from the atmosphere will have a “very limited role” in the fight against global warming, according to a new study by the American Physical Society. While it is technically feasible to pull CO2 from ambient air — as opposed to capturing and sequestering emissions directly from power plants — the costs will remain too high to make it a viable option for decades to come, researchers say. The study said that pulling CO2 from the air costs about $600 a ton, compared with roughly $80 a ton to capture it directly from the flue gas of a coal-fired power plant. The most significant challenge is the low concentration of CO2 in the atmosphere; while flue gas from a coal plant contains about 10 percent CO2, concentrations in ambient air are only about four-hundredths of a percentage point. “We have to deal with our centralized power sources first,” said Robert Socolow, a Princeton researcher and co-chair of the study. Advocates of direct air capture, however, say the technology remains in its early stages and that it would be a mistake to write it off as an option in reducing CO2 concentrations in the atmosphere.