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Greta Thunberg arrives in Lisbon to make it to COP25

Travel is tough when you're trying to cut your carbon footprint. No one knows that better than climate activist Greta Thunberg, who willingly gave up airline flights due to the industry's impact on accelerating climate change. To cross oceans, she's had to travel by sailboat — a charmingly old school way to get around, but a challenge when you're trying to make it to a United Nations climate summit on time. Today, after three weeks of sailing on the ocean, news publications have reported that Thunberg has made it from the U.S. to her first European destination in Lisbon, Portugal.

Her initial travel plans to head down to Chile through North and South America were shaken up after the U.N. changed the climate summit from Chile to Madrid on short notice. Thunberg ended up asking the public for assistance on social media. She eventually found an Australian family of vloggers and a professional yachtswoman who offered to give her a lift on their yacht. Their boat had amenities, hydro-generators, and solar panels that kept its emissions low. Perfect for a climate change activist.

Although international travel can be tricky, avoiding airplanes isn't always so difficult. In the U.S., after making a big splash arriving on U.S. shores via sailboat, Thunberg traveled around in a Tesla provided by a starstruck Arnold Schwarzenegger. When she was in Europe, Thunberg was able to rely on trains to travel around. According to the BBC, "[train travel] virtually always comes out better than plane" travel with some flights producing 2-3 times more carbon emissions than trains. Possibly even more than that, if the trains are run by renewable electricity. The emissions produced by trains are so much less in comparison to plains, in fact, that some economists have said ticket prices should be adjusted to factor the carbon cost of travel. This would make plane tickets consistently more expensive than train tickets.

Some airlines have tried to make adjustments to offset the amount of carbon emissions caused by planes — such as retiring old, energy-inefficient planes — but there's still much work to be done. Until then, airplanes are still off-limits to Thunberg, and she'll continue to find ways to get around thanks to the people who support her.