On June 25th, 1981 I was working as a wilderness ranger near the top of 10,600 ft. Sandia Peak outside Albuquerque. There were thunderheads building, and we saw a couple of hang glider pilots preparing to take off. A couple of the rangers I was with went over to talk to them, and told them they were doing something really stupid.
The pilots didn’t listen, and took off anyway. One of them got carried up to 40,000 feet and was found frozen solid about 10 miles away. He turned into a giant hailstone. The other escaped by doing a near free fall down the cliffs.
Police said Abbott was in a drift of ice when they found him
27 Jun 1981, Page 6 – Detroit Free Press at Newspapers.com
It was the second hottest day of the summer, and one of the hottest days on record in that region.
Despite the high temperatures near the ground, it was very cold at altitude. Just like on Venus. temperature in Earth’s troposphere increases linearly with altitude. At an altitude of 50km in the Venusian atmosphere, the temperature and pressure is about the same as at Earth’s surface.
http://www.datasync.com/~rsf1/vel/1918vpt.htm
Tropospheric temperature correlates with pressure, not chemical composition. Had Steven Hawking understood some of the most basic principles of science, he would have known this.