Danish physicist Henrik Svensmark studies what happens to Earth when its magnetic shield weakens. He says the poles fully flip roughly every 700,000 years. The

Danish physicist Henrik Svensmark studies what happens to Earth when its magnetic shield weakens. He says the poles fully flip roughly every 700,000 years. The last near flip was 39,000 years ago. Here's what it does to the climate: [▻](https://video.twimg.com/amplify_video/2085444075193307136/v…