From 2010 to 2011 United Airlines’ fuel efficiency dropped 2.3 percent, according to the country’s 2011 sustainability report.

In 2010 the company used 0.155 gallons of fuel per revenue ton mile, and in 2011 this figure increased to 0.159. However, United says that it currently leads US carriers in this metric. The company recorded 3.1 percent fewer revenue ton miles from 2010 to 2011, but used just 0.9 percent less fuel over that time period.

The company’s scope 1 carbon intensity rose 1.9 percent in 2011, from 1.54 to 1.57 metric tons of CO2e per 1000 revenue ton miles. The increase in emissions intensity comes despite a 0.9 percent drop in the airline’s absolute scope 1 emissions. That metric fell from 33 million metric tons in 2010 to 32.7 million metric tons in 2011. (See chart, below)

Scope 2 emissions rose 7.8 percent year-on-year from 214,690 tons to 231,389 tons. This increase was down to a jump in the company’s electricity consumption rather than a switch in energy source, figures show. United’s absolute Scope 3 emissions dropped 0.5 percent year-on-year.

More than 98 percent of United’s greenhouse gas footprint comes from fuel use. As such, the company says that much of its sustainability work focuses on reducing fuel consumption and increasing fuel efficiency. Since 1994 the company says it has improved its fuel efficiency by 32 percent. United says the most effective way it increases fuel efficiency is by replacing older aircraft with newer, more fuel-efficient airplanes. The company expects to to take delivery of more than 270 new airplanes through 2022, including Boeing’s new 787 Dreamliner airplane, which should use 20 percent less fuel than those aircraft it replaces.

In addition to the new, incoming aircraft, the airline has equipped more than 300 aircraft with winglets that result in up to a 5 percent increase in fuel efficiency, and a reduction in emissions and noise. The company has also modified 20 Boeing 777 aircraft with a performance improvement package aimed at improving airplane aerodynamics, offering greater fuel efficiency and lower carbon emissions, United says. A further 52 777s are set for future modification.

In terms of operational efficiency United has worked to reduce the use of fuel-driven thrust reversers on landing, increase the use of single engine taxiing, and increase the use of ground equipment rather than aircraft engine power to move aircraft between gates.

Efficiency measures have been undertaken at on-ground facilities as well, despite these areas contributing only a small part of the company’s carbon footprint. Through 2010 the company relocated customer facilities at 20 airports, reducing its leaseholds by 300,000 square feet in an effort to cut energy use. Through the use of energy efficiency materials and technology, Terminal E, located at the airline’s Houston hub, is around 15 percent more energy efficient than a traditional terminal.

The company’s waste production rose 24.8 percent year-on-year from 10,845 tons in 2010 to 13,357 in 2011. However, in that time the amount of regulated waste created dropped 21.4 percent, while the amount of recyclable waste United produced jumped by 50.5 percent, the report says.

Through on-board programs, United has recycled more than three million pounds of cans and plastic items over the past five years. On the ground the company has developed a network that recycles mixed paper, aluminum, plastic bottles, oil, paint, pallets, plastic sheeting, cardboard, scrap metal and cooking oil. The company also donates unused food items to local food banks, used uniforms to make new clothing products or accessories, and computers for reuse in public schools, the report says.

Strong progress has been made on the company’s local air quality metric. From 2010 to 2011 United’s global NOx emissions dropped 6.2 percent from 16,908 to 15,865 tons. The airline’s mainline aircraft contributed most of the metric, followed by on-ground vehicles and finally United’s facilities.

United Continental, American Airlines and industry association Airlines for America this year dropped a lawsuit challenging US airlines’ inclusion in the European Union’s Emissions Trading Scheme. Airlines for America, whose members include Delta, Southwest, US Airways, FedEx and UPS, as well as industry partners Airbus, Boeing, Honeywell and Pratt & Whitney, said that opposition to the European law has grown so much that governments should now take the lead, instead of companies pursuing the matter through the courts.