Hainan Airlines and All Nippon Airways ranked first in fuel efficiency among transpacific carriers in 2016, according to a report released Tuesday by the International Council on Clean Transportation.

The new report analyzed 20 airlines operating nonstop flights between the mainland U.S. and East Asia and Oceania. The difference in efficiency performance between the most and least fuel-efficient carriers was 64 percent.

"The colossal gap between the most and least fuel-efficient airlines shows that dramatic pollution reductions are easily within reach using existing technologies," said Vera Pardee, senior counsel at the Center for Biological Diversity's Climate Law Institute. "By flying less-polluting carriers like Hainan and All Nippon, we can all reduce our carbon footprint while giving delinquent airlines an incentive to adopt their competitors' more climate-friendly practices."

Airlines analyzed in the study cut fuel use and carbon pollution through a number of strategies, including buying new aircraft, increasing passenger density and optimizing freight load.

Aviation already accounts for at least 2.5 percent of global greenhouse gas pollution, and the industry's emissions are rising steeply. If commercial aviation were considered a country, it would rank seventh after Germany in terms of carbon emissions. Airplanes could generate 43 metric gigatons of planet-warming pollution through 2050, consuming more than 4 percent of the world's remaining carbon budget, according to a Center for Biological Diversity report.

The first international standards for carbon pollution from airplanes were adopted by the International Civil Aviation Organization in early 2017. But these standards will reduce emissions from new planes less than "business as usual" and do not apply to any in-service aircraft.

"Aviation emissions continue to skyrocket, yet international fuel-efficiency standards are disturbingly weak," Pardee said. "We need to push for stronger policies to reduce the climate harms of airline travel. But in the meantime, consumer demand is a powerful tool to pressure the industry to curb its dangerous pollution."