(CNN) — In the early days of the pandemic, when demand for air travel abruptly flatlined and international borders closed, "ghost flights" became a common phenomenon.
These were empty or near-empty planes traversing the skyline as airline schedules kept to their contractual obligations to fly. The problem is that, nearly two years on, they're still haunting the skies above us.
In fact, more than 100,000 "ghost flights" will sail over European skies this winter, according to recent analysis from Greenpeace. The climate damage, claims the environmental group, is "equivalent to the yearly emissions of more than 1.4 million cars."
The Greenpeace figures are extrapolated from a December interview with Lufthansa CEO Carsten Spohr in which he warned that Lufthansa Group was facing the prospect of 18,000 superfluous flights over the six-month winter season to retain its slots under European rules.
On the basis that Lufthansa's air traffic accounts for 17% of the European market, Greenpeace reckons the total number of Europe's ghost flights would generate 2.1 million tonnes of CO2.
The analysis has triggered a torrent of outrage. Campaigner Greta Thunberg asserted that "Brussels Airlines [part of the Lufthansa group] makes 3,000 unnecessary flights to maintain airport slots." In the UK, a petition was launched, appealing to the government to ground unoccupied flights.
Lufthansa, meanwhile, says it's doing its best to fill all its aircraft, but was struggling to balance Covid chaos with the need to hold onto its slots.
"Unnecessary flights are not empty or 'ghost' flights," a spokesman for the airline told CNN. "They are scheduled flights that are poorly booked due to the pandemic. Despite poor demand, Lufthansa Group Airlines must operate these flights to continue securing takeoff and landing rights at hubs and major EU airports."
Lufthansa says that the emergence of the Omicron variant is the reason its projections for the season ahead were so far short of the reality. The crisis "led to significantly increased travel restrictions and cases of illness in the general population and among employees," says its spokesperson. "This unexpectedly not only reduced the prior trend of recovery, but also triggered a significant slump in demand."
Last October, the aviation industry pledged at the International Air Transport Association (IATA) annual meeting to achieve net-zero carbon emissions by 2050.
Numerous players -- including hub-based carriers, low-cost airlines, regulators and environmental lobbyists -- are at loggerheads in a multi-way blame game over the absurd wastefulness of unnecessary flights.
"We're in a climate crisis, and the transport sector has the fastest-growing emissions in the EU -- pointless, polluting 'ghost flights' are just the tip of the iceberg," says Herwig Schuster, spokesperson for Greenpeace's "European Mobility For All" campaign.
"It would be irresponsible of the EU to not take the low-hanging fruit of ending ghost flights and banning short-haul flights where there's a reasonable train connection," he adds.
So why on Earth are these Mary Celeste flights still ongoing -- and what are aviation's stakeholders doing to disentangle themselves from the red tape that has ensnared the airlines into this climate-damaging mess?