Ramaswami: Airlines face an unprecedented international crisis in the wake of the coronavirus pandemic. The International Air Transport Association estimates that the global industry will lose $252 billion in 2020. Many airlines are cutting up to 90% of their flight capacity. On March 1, more than two million people in the United States were flying per day. A month on, fewer than 100,000 people are going through airport security daily. Some climate activists have welcomed the emptied skies, pointing to the dramatic fall in carbon emissions. But others worry that the bounce back and attempts to take back some of the losses might mean that an opportunity for fundamental, sustained change may be missed.