Tesla has built one of the biggest buildings on the planet. Now it's building the world's largest solar roof to top it off. When it's complete, the photovoltaic array will enable Tesla's Gigafactory to operate entirely on clean energy. Meanwhile, the Netherlands announced that wind energy now powers all of its electric passenger trains, and the UK is developing technology to power its trains with off-grid solar. As Inauguration Day approaches, many are worried about the future of clean energy in the US, but Elon Musk thinks the Trump administration may be "positive on renewables," and President Obama reassured the public that the US' clean energy transition is "irreversible."

Could the skyscrapers of the future purify polluted cities? That's the idea behind this futuristic tower that eats smog and spits out fresh air. Meanwhile, a shopping mall in Israel has built a flourishing rooftop farm that can produce 10,000 heads of lettuce a month. Elsewhere in the world, the largest survival community on Earth has built a massive compound of 575 off-grid doomsday bunkers, and we featured six amphibious houses that literally lift off the ground to escape flooding. In other design and technology news, MIT developed an ultralight material that is 10 times stronger than steel, and Aerochromics launched a line of clothing that changes color when it's exposed to air pollution.