'Flight shaming' is a Swedish-born movement that calls for curbs to air travel due to its environmental impact.

The number of passengers who flew through Swedish airports fell four percent in 2019, Swedish state-owned airport operator Swedavia said on Friday, with the drop led by a decline in domestic traffic.

The Swedish-born movement of "flight shaming", which calls for curbs to air travel due to its environmental impact, has gained prominence over the past year and the aviation industry is closely watching travel trends in countries such as Germany and Sweden, where the campaign has begun to have an impact.

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"We see a number of reasons concurring, such as the Swedish aviation tax, [a] weak Swedish crown, [and] softening economy worries. But also the climate debate," Swedavia spokesman Robert Pletzin said. He added the drop followed a record number of passengers in 2018 and several years of strong growth.

More than 40 million passengers travelled through 10 Swedavia airports, down from the previous year's all-time high above 42 million, with domestic travel down nine percent, the airport operator said in a statement. Domestic travel fell for the second year in a row.

In December, domestic travel fell by seven percent and overall traffic was down four percent.

Germany has seen similar trends, with ADV industry group predicting a 2.9 percent fall in takeoffs and landings at German airports in 2020.

The anti-flying movement emerged in 2017 after Swedish singer Staffan Lindberg pledged to give up flying and the movement has spread amid increasing concerns over global warming, adding the Swedish term "flygskam", or "flight shame", to the vocabulary. Teenage climate activist Greta Thunberg last year sailed across the North Atlantic twice to avoid flying.

Swedavia did not comment on the campaign in its statement, but highlighted its environmental efforts, saying all of its airports will have zero carbon emissions from their operations this year.

Over the course of last year, analysts have been increasingly factoring a potential backlash against air travel into industry outlooks. In September, Citi said greater consumer awareness about global carbon emissions has already had a tangible effect in Sweden and could call into question the longer-term growth potential of the entire industry.

Exane BNP Paribas warned said in November European airlines face pressure from some consumers seeking alternative means of transport.

The anti-flying movement's growing momentum has put the aviation industry on the defensive. In November, International Air Transport Association, the industry's global body, said it would launch a campaign aimed at countering the industry's negative image and promote its efforts to curb carbon emissions.