That’s one explanation being given why more jets than last year are expected to carry executives, world leaders, and other luminaries this week to the Swiss Alpine town of Davos for the World Economic Forum.

It’s also a bit ironic since jets contribute to global warming and curtailing climate change is one of the leading topics on the forum’s agenda.

At least 1,500 private jets are slated to arrive in Davos, according to the Air Charter Service. The number is up from last year’s estimated 1,300. The ACS also says this year’s jets are larger and more expensive.

Why more and bigger jets?

“This is at least in part due to some of the long distances traveled, but also possibly due to business rivals not wanting to be seen to be outdone by one another,” Andy Christie, the private jets director at ACS, said in a statement. “The week of the forum is unlike any other busy private jet event, such as the Super Bowl or Champions’ League final.”

For its report, the charter service surveyed four airports near the forum, in Zurich, Dubendorf, St. Gallen-Altenrhein and St. Moritz.

The economic forum disputes the charter service’s conclusions, after reviewing flights at two airports near the event, in Zurich and St. Gallen-Altenrehein.

The forum claims that 135 roundtrip private flights this week are expected to bring Davos attendees, a 14% decline from last year. Their analysis is based not on number of jets, but a measurement called air traffic movements.

Still, the impact of Davos attendees’ private jets “is a question that always gets asked. And so it should, From an environmental perspective, taking a private jet is the worst way to travel to Davos,” according to a forum news release. “It’s also a complicated question, as the data is not always easy to determine.”

The forum said it takes environmental steps to offset carbon emissions generated because of the economic summit.

Over the past five years at Davos, countries with the highest numbers of private jet arrivals and departures include Germany, France, United Kingdom, United States, Russia, and the United Arab Emirates, according to ACS.

Air travel adds a significant amount of greenhouse gases into the atmosphere, with nearly 25% of emissions occurring during landing and take-off, according to a 2010 report from NASA.

The high-profile Davos confab started Monday with naturalist and broadcaster David Attenborough urging attendees to take action against global warming before it’s too late. “What we do now, and in the next few years, will profoundly affect the next few thousand years,” he implored, the Guardian reported.

The effects of global warming are well known to the World Economic Forum. Its own Global Risk Report, published earlier this year, identified climate change and environmental degradation as “the gravest threats” over the next 10 years.