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In dozens of archaeological discoveries around the world, from the once-successful reservoirs and canals of Angkor Wat in Cambodia to the deserted Viking colonies of Greenland, new evidence paints pictures of civilizations struggling with unforeseen climate changes and the reality that their farming practices had become unsustainable. Among these discoveries are also success stories, where ancient farming practices helped…

Hydrogen is often heralded as a climate hero because when it’s used as a fuel in things like buses or steel production, there are no direct carbon emissions (or related warming) to worry about. As the world tries to cut down on our use of fossil fuels, there could be plenty of new demand for this carbon-free energy source. But how hydrogen is made could determine just how helpful it is for the climate. That’s where the rainbow comes in. (I’ve added an at-a-glance table below so you can untangle all these colors.) …