Why plane turbulence is really becoming more frequent and severe

BBCAndrew Davies was on his way to New Zealand to work on a Doctor Who exhibition, for which he was project manager. The first leg of his flight from London to Singapore was fairly smooth. Then suddenly the plane hit severe turbulence."Being on a rollercoaster is the only way I can describe it," he recalls. "After being pushed into my seat really hard, we suddenly dropped. My iPad hit me in the head, coffee went…