Air travel experts estimate that as many as 1,500 private jets will be coming and going from a Swiss Ski resort hosting the annual meeting of the World Economic Forum in Davos this week, the Guardian reports. In addition to the sheer volume of the costly and fuel-hungry aircraft, the jets themselves appear to be bigger and more expensive than those used in past years.

In general, private jet travel to the event has increased by about 11 percent year over year, according to the Air Charter Service (ACS), which charters aircraft for cargo and private use.

“There appears to be a trend towards larger aircraft, with expensive heavy jets the aircraft of choice,” said Andy Christie, private jets director at the ACS. “Gulfstream GVs and Global Expresses [were] both used more than 100 times each last year.”

The increasing use of private jets is drawing particular scrutiny this year, as the forum’s global risk report lists environmental concerns — including failure to address climate change — as the number one threat to the global economy. Jet travel has been identified as a substantial contributor to climate change, per Deutsche Welle.

Many eyes are presently on this gathering of global leaders as they consider options to preserve the environment.

“There is more power in this room than any gathering anywhere,” esteemed naturalist Sir David Attenborough said to attendees as part of the conference. “The people here need to do something about the natural world.”

Although leaders have prioritized further discussion of environmental issues as a central part of the event, this concern has not yet carried over to travel plans, generally speaking.

1,500 private jets expected at Davos, despite global warming being a major concern https://t.co/CQHJhqMDjC — MarketWatch (@MarketWatch) January 22, 2019

While ACS attributes the length of travel for some attendees as a driving factor in the increased use of larger and more comfortable private aircraft, Christie also points out the possibility of escalation “due to business rivals not wanting to be seen to be outdone by one another.”

Another potential contributor to the higher volume of jets is the increasing trend of “jet-sharing” services — services which allow individuals to purchase partial shares in shared aircraft, meaning that private jet travel is no longer a luxury only available for the ultra rich. For an even lower cost option, subscriptions can also be purchased, providing access to private travel without an ownership stake.

In any case, climate scientists and advocates continue to monitor the words and actions of conference attendees, whose support — or lack thereof — could substantially influence the trajectory of global climate issues in the years to come.

“What we do now, and in the next few years, will profoundly affect the next few thousand years,” said Attenborough.