I met the aerobically inclined climate scientist on the road last week in northern France. He ran (he is on his fourth pair of shoes) while I biked behind him, struggling to keep up.

Freezing rain and snow pelted our faces as we traveled past misty fields, tile-roofed villages and Edward Scissorhands shrubbery. The whole thing was exhausting, but Knudsen, a 29-year-old with sandy hair, a scraggly beard and a Spandex-meets-DayGlo wardrobe, wasn't fazed by any of it. He seemed to thrive on the Fargo-like conditions.

"I love the snow!" he said, darting up a hill.

These are difficult times, as I don't need to remind you. ISIS is on everyone's mind, especially here in France, where at least 130 people were killed in a recent terror attack. Fear cloaks this country like a persistent fog, and many observers worry that the threat of terror will infect the upcoming U.N. climate change summit, called COP21, which begins Monday in a Parisian suburb.

But spending a day with Knudsen gave me a healthy dose of optimism in addition to sore thighs. There's ample reason to believe the U.N. talks will help shove the world off of fossil fuels and toward a cleaner future. All we have to do is what Knudsen recommends: Put one foot in front of the other, remember why we're here, and carry with us an important collection of stories.

Another form of terror

Like Knudsen's past several months, my year has been a prelude to the Paris summit.

But with, you know, less running.

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I've spent most of 2015 taking your questions about climate change and turning them into stories as part of CNN's Two° series . If you've been reading along, you know that 2 degrees Celsius is the number at the center of the upcoming Paris negotiations.

Pretty much every country in the world has signed a treaty saying that 2 degrees Celsius of warming, measured since the Industrial Revolution, is all we can tolerate. Cross that line, and we're expected to supercharge droughts, make storms more intense, commit low-lying islands to a watery death as seas rise, push millions more into poverty and put many plants and animals at risk of extinction. It's not an exact trigger point (1.9 degrees of warming is monumentally less catastrophic than 2.1 degrees, for instance), but diplomats had to draw a line in the sand.

And everyone agrees that 2 degrees of warming is too much.

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Yet we don't act like it. We've already warmed the climate about 1 degree Celsius. We're essentially locked into 1.5 degrees of warming based on all of the pollution we've pumped into the atmosphere, primarily by burning fossil fuels for heat and electricity. And pollution-reduction pledges logged by more than 140 countries in advance of the Paris talks promise to slow warming only to an estimated 2.7 degrees by the end of the century

We humans, however, are excellent at ignoring long-term global problems -- like climate change. We focus on what's right in front of us. The recent terror attacks are tragic, and many lives will never be the same because of them. They should not be minimized.

But climate change is another form of terror -- and it's one we're wreaking on ourselves.

'Worst-case scenario'

Being pessimistic about that is understandable, especially since previous attempts to use international politics to fix the climate problem largely have failed.

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Before I spent a day with the running climate scientist, I spoke with Yvo de Boer , former head of the United Nations Framework Convention on Climate Change, the group that gets diplomats together to talk about the climate crisis. De Boer famously was moved to tears when a previous round of climate negotiations started to collapse.

"There's a certain risk that political ambition trips over bureaucratic complexities," he told me by phone. "There is this 50-odd-page document, which still contains many areas of disagreement. That stands between the beginning of the Paris conference and a successful outcome at the end. Very often at these conferences, the devil is in the detail.

"My worst-case scenario," he continued, "is the one that we seem to see at almost every climate conference, which is that it needs to go into significant overtime."

With 2 degrees on the horizon, there's no time for delay.

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Recently, there was much optimism ahead of the Paris climate talks. China and the United States, the world's two biggest polluters, have pledged significant cuts in carbon pollution. The Obama administration rejected the Keystone XL pipeline , which was a symbolic boost for efforts to get the world off of dirty fuels like oil and coal. The Pope has been helping people finally see climate change as a moral crisis , one that will hit the world's poor the hardest. And solar power is getting much cheaper.

But along came ISIS. Now, massive public demonstrations at COP21 have been canceled, and a malaise hangs over the entire process.

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Knudsen, the running climate scientist, thought about abandoning his Pole to Paris journey because of the terror attacks on November 13 . He canceled public events he'd planned in Brussels, and he knows that his arrival in Paris probably will be met with little fanfare. He'd imagined hundreds of people running with him into the French capital. Now he's not sure whether his arrival, probably later this week, he told me, will be noticed by much of anybody ( You can follow his progress on the Pole to Paris website , as well as the path of a colleague biking from New Zealand). When I met him in Maubeuge, France, on November 23, he gave a talk to a room of 50 chairs, all but six of them empty.

It's clear the world's attention was elsewhere.

'Pole to Paris'

"Great weather!" Knudsen yelled back at me as we crested a snowy hill.

He did that kind of thing all day.

He somehow found energy to grin constantly and cheer me on while I sweated through six layers of clothing, struggling to do once, on a bike, what he does daily on foot.

Photos: The illustrated guide to saving the planet Photos: The illustrated guide to saving the planet #CNNGoGreen –



It's estimated that over 90 million pieces of clothing end up in landfills each year. You can reduce your impact by avoiding synthetic fibers (made from damaging chemicals) and buying clothes made with natural fibers such as cotton or wool, which break down in landills. And as fashion sustainability champion Vivienne Westwood said simply, "Choose well, buy less." As world leaders prepare to make major promises on climate change, CNN wants to know the little ways that you try to help the planet. Here are our ideas - what are yours? Share your tips with #CNNGoGreen It's estimated that over 90 million pieces of clothing end up in landfills each year. You can reduce your impact by avoiding synthetic fibers (made from damaging chemicals) and buying clothes made with natural fibers such as cotton or wool, which break down in landills. And as fashion sustainability champion Vivienne Westwood said simply, "Choose well, buy less." Hide Caption 1 of 10 Photos: The illustrated guide to saving the planet #CNNGoGreen –

It's not just in terms of the methane cows produce -- they also require lot more water and land than sheep, chicken or pigs, which causes deforestation.

Beef is one of the livestock that takes a big toll on the environment. The UN estimates that cattle rearing and slaughtering accounts for 65% of the meat industry's greenhouse emissions.It's not just in terms of the methane cows produce -- they also require lot more water and land than sheep, chicken or pigs, which causes deforestation. Hide Caption 2 of 10 Photos: The illustrated guide to saving the planet #CNNGoGreen – Buying something brand new uses up resources, while trashing something causes further waste. Electronics can be repaired, clothing can be mended and furniture upcycled or restored.

Hide Caption 3 of 10 Photos: The illustrated guide to saving the planet #CNNGoGreen – Put your money where your mouth is! Commercial interest in renewables is on the rise. The Collaborating Centre for Climate & Sustainable Energy Finance reported a 17% surge in global investments in green energy last year, which is now worth $270billion worldwide. Hide Caption 4 of 10 Photos: The illustrated guide to saving the planet #CNNGoGreen – If you can't avoid producing significant emissions, try to make up for it. This isn't only through planting trees -- you can also use green energy in your home or invest in hydro or wind power. Hide Caption 5 of 10 Photos: The illustrated guide to saving the planet #CNNGoGreen – The transportation sector accounts for 27% of all greenhouse gas emission in the U.S. alone . So unless the face-to-face meeting is absolutely necessary, stay put. Hide Caption 6 of 10 Photos: The illustrated guide to saving the planet #CNNGoGreen –

According to British NGO Waterwise , some old-fashioned toilets use 13 liters of water every flush -- over 6 times the amount of the recommended daily use. Using a dual flush toilet can save water. Switching to a "low flow" shower head reduces the amount of water usage, and maintains the power of a normal shower. Hide Caption 7 of 10 Photos: The illustrated guide to saving the planet #CNNGoGreen – The number of vehicles available through car-sharing schemes looks set to increase -- helping you save money while also saving the planet. With handbags, outfits, power tools and bikes all available to borrow, the "shareconomy" is in full swing. Hide Caption 8 of 10 Photos: The illustrated guide to saving the planet #CNNGoGreen – International shipping and transport contributes to around 25% of the CO2 emissions of most developed countries. The ingredients of local food and drinks are easier to trace too, while you can feel good about supporting local producers. Hide Caption 9 of 10 Photos: The illustrated guide to saving the planet #CNNGoGreen – #CNNGoGreen.

Will Worley contributed to this story.

Heating not only produces CO2, but also nitrogen oxides -- which are 300 times as powerful in warming the planet. In the U.S ., 12% of all sulfur dioxide and nitrogen oxides emissions are caused by cranking the heat. Added bonus: Using smart tech to save energy in the home means you'll save cash on bills. What are your green tips? Let us know on Facebook, Twitter or Instagram with the hashtagWill Worley contributed to this story. Hide Caption 10 of 10

He told me he's always been drawn to extremely remote, cold places, which I guess makes sense for a Norwegian guy who studies the Arctic. His unyielding optimism could be annoying if it weren't so genuine. It starts to become contagious. By the end of the day, I found myself happily swishing through puddles on the bike, trying to give back some encouragement to Knudsen and two friends -- Zoé Favart, 25; and Oria Jamar de Bolsée, 24 -- who were joining him on this part of his European expedition.

His sunny demeanor has a clear source. Each morning, before lacing up his shoes and putting on still-wet clothes from the day before, Knudsen asks himself two questions: "What's the goal of the day?" And "Why am I doing this?"

The answer to the first question often is fairly obvious: Today I want to survive, give an interesting presentation or tolerate a pesky CNN crew.

Photos: Are cars in cities a thing of the past? Photos: Are cars in cities a thing of the past? Paris' usually jam-packed roads went car-free for a day on September 27. Hide Caption 1 of 8 Photos: Are cars in cities a thing of the past? Madrid's vehicle-free zone now extends to over one square mile to reduce the pollution that sometimes covers the city with a murky brown film. A plan to close off 24 of the city's busiest streets is likely to be approved early next year. Hide Caption 2 of 8 Photos: Are cars in cities a thing of the past? Hong Kong is mulling over plans to make one section of its bustling downtown a bit more eco-friendly. A range of civic groups have proposed to make Des Veoux Road in Central, a major city artery, pedestrian-only. Hide Caption 3 of 8 Photos: Are cars in cities a thing of the past? Trams will be the only kind of vehicles allowed in the zone, if the concept was approved. Members of the public will be asked to vote for their favorite plan next month. Hide Caption 4 of 8 Photos: Are cars in cities a thing of the past? China may perform miserably overall when it comes to air pollution but by 2020, this is what Great City, a town outside of Chengdu, China is projected to look like. It's been designed so that the distance between any two points in the city should be walkable within about 15 minutes, eliminating the need for cars. Hide Caption 5 of 8 Photos: Are cars in cities a thing of the past? Scheduled for completion in 2020, it will accommodate up to 80,000 people, planners Adrian Smith + Gordon Gill Architecture Designs said, and residents can make use of a system of electric shuttles. Hide Caption 6 of 8 Photos: Are cars in cities a thing of the past? Abu Dhabi in the UAE is building what they say will be the world's first zero-carbon city. Not only will it be free of cars and skyscrapers, it will be solar-powered. Hide Caption 7 of 8 Photos: Are cars in cities a thing of the past? Emiratis will have to give up their gas-guzzling SUVs in this town. The city plans to use driverless electric pod cars to transport people. Hide Caption 8 of 8

The answer to the second is more interesting. It usually has something to do with the people Knudsen has met en route. Like Laila Inga, an indigenous woman in the Arctic who, he told me, is having trouble surviving as a reindeer herder because of changes in the climate.

The snow is melting and refreezing more often, he said, making it difficult for reindeer to nuzzle through the ice to reach the vegetation hiding below.

Knudsen feels a responsibility to carry Inga's story to Paris.

I feel similarly obliged to be a vessel for stories from the front lines after visiting, on your behalf, places that will be destroyed by 2 degrees of warming ( the Marshall Islands ) as well as those helping us beat that goal ( a reservation in Montana ).

I hope someone in Paris is ready to listen.