Slovenian adventurer and environmentalist Matevz Lenarcic on Sunday became the first person to fly an ultra-light plane from Europe to America and back over the North Pole, as he landed in Ljubljana after an epic voyage.

"I've had more trouble than I had expected, and that prolonged the expedition but what matters is that me and the plane have arrived safely," the 54-year-old told a crowd of well-wishers.

But his month-long journey was not all plain sailing.

The trained biologist had to make an unscheduled stop in Saint-Nazaire, northwestern France, due to weather conditions and an Irish airport did not have the type of fuel required for his aircraft.

But after a two-day wait in France waiting for favourable weather conditions, Lenarcic took off from Saint-Nazaire earlier Sunday and finally landed in Ljubljana from where he had departed on April 22.

"I've had many unexpected events. That is why this trip has taken 14 days longer than initially planned," Lenarcic said Thursday on arrival at Saint-Nazaire.

The plane was equipped to measure air pollution over the North Pole -- a hot-spot for global warming -- and Lenarcic said all measurements had gone as planned.

While flying over the Arctic, an important indicator of global weather changes, Lenarcic was surprised to notice that "temperatures on the actual North Pole were much higher than in surrounding areas."

An accomplished aerial photographer, Lenarcic took pictures and measured levels of black carbon and light-absorbing particles over the Arctic at a height of 3,000-4,000 metres (9,800-13,000 feet), an altitude rarely explored by scientists.

These particles -- mostly the product of burning coal and other fossil fuels -- absorb light from the Sun and thus play a role in the complex equation of global warming.

The 15,600-kilometre (9,700-mile) scheme was initiated last year after Lenarcic succeeded in circling the world in the same aircraft, a Pipistrel Virus SW914, which weighs just 290 kilogrammes (640 pounds) unladen.