Areas of the planet home to one-third of humans will become as hot as the hottest parts of the Sahara within 50 years, unless greenhouse gas emissions fall, according to research by an international team of scientists with participation from Aarhus University published in the journal Proceedings of the National Academy of Sciences this week. The rapid heating would mean that 3.5 billion people would live outside the climate ‘niche’ in which humans have thrived for 6,000 years.