Airlines are doing too little in the fight against global warming, a study funded by investors with $13 trillion in assets under management said on Tuesday.

The fast-growing sector accounts for 2 percent of world greenhouse gas emissions and should do more to manage risks of climate change, the Transition Pathway Initiative (TPI) said in a review of 20 of the world's biggest listed airlines.

It rated Delta, Lufthansa, United Airlines and ANA Holdings as the best performers at managing the business risks and opportunities of climate change. But all could do more.