Dozens of people, many dressed in penguin costumes, are staging a sit-in at Berlin's Tegel airport to protest against greenhouse gas emissions from air travel.

About 50 members of the group Am Boden Bleiben — German for "stay grounded" — gathered Sunday in the airport's main entrance and were quickly surrounded by police.

Climate activists argue that air travel is disproportionately responsible for emissions of carbon dioxide and other gases blamed for global warming and should be drastically reduced in countries where alternative means of transport are available.

Airport spokesman Hannes Hoenemann said the protest had "no impact" on flights.