The World Economic Forum has begun in the luxury ski resort of Davos, Switzerland. On Monday, climate activists blocked a private jet airport used by many to reach the annual conference. According to Greenpeace, over 1,000 private jets flew in and out of Davos during last year’s gathering.

Meanwhile, over 700,000 people have signed an open letter to fossil fuel CEOs attending the World Economic Forum, urging them to “immediately stop opening any new oil, gas, or coal extraction sites, and stop blocking the clean energy transition.” The letter was written by a group of climate activists including Vanessa Nakate of Uganda and Greta Thunberg of Sweden.