Physicist William van Wijngaarden has ignited a controversy by challenging a supposed prime example of man-made climate change – that jet condensation trails, know as contrails, act like clouds, cooling the Earth during the day and keeping it warmer at night.

He examined the spread between day and night temperatures from 112 weather stations across Canada for Sept. 8 to 17 in 2001, and discovered there wasn’t a spike during the no-fly period after 9/11.

Instead, Wijngaarden found the temperature range at stations across southern Canada both increased and decreased in the contrail-free days after the post 9-11

“The American researchers need to look a bit harder at the original data,” Wijngaarden said.

The lead researcher on the original U.S. study told the Star yesterday that the negative results from Canada don’t necessarily undermine his group’s findings.

“It’s possible that Canada simply doesn’t have a high enough density of jet traffic for contrails to make any difference,” said David Travis, a geography professor at the University of Wisconsin in Whitewater.

But Travis said he had not realized Pearson Airport has been ranked 20th busiest airport in the world measured by takeoffs and landings.