UN chief Ban Ki-moon visited Wednesday a vault carved into the Arctic permafrost, filled with samples of the world's most important seeds in case food crops are wiped out by a catastrophe. "The world faces many daunting challenges today, one of the greatest of which is how to feed a growing population in the context of climate change," a bundled-up Ban told reporters after he toured the site in the Svalbard archipelago some 1,200 kilometres (745 miles) from the North Pole....