The EM Drive is a proposed method of creating thrust without any propellant. Physicists agree it is impossible, but there is some convoluted math that shows it can work. After it was proposed, a couple of scientists in China said they tested it and it worked. Everyone scoffed. NASA set about to prove it wouldn't work but failed in the first set of tests because it did indeed create a measurable thrust. There were complaints that it wasn't done in a vacuum. So they did it in a vacuum and it worked again. Most are convinced it can't possibly work because of the laws of physics i.e. conservation of momentum. It is an interesting thing to follow as scientists try to demonstrate it can't work. I am skeptical but know there have been times in the past when the laws of physics, as they were understood at the time, were shown to be slightly different than generally thought.
A great method to check on future developments is to search for "em drive nasa" in google news.
Since about 1976 the areal extent of sea-ice in the Northern Hemisphere has varied about a constant climatological level but in 1972-1975, sea-ice extent was significantly less - IPCC 1990 assessment, Page 224.