The Blue Ridge Parkway is 469 miles of beautiful vistas, a mountainous road that winds from Virginia to North Carolina in the USA. The route is peppered with elevation signs, telling you how many metres above sea level you are. Which has CrowdScience listener Beth wondering: as we are told that sea level is rising, will all the elevation signs need repainting? It’s a task she’s passed over to the CrowdScience team, who like a difficult challenge. The height of an enormous pile of rock like Ben Nevis, or Mount Everest feels unchangeable. But we measure them relative to the nearest patch of sea, which is where our story becomes complicated. Unlike water in a bath, sea level is not equal around the world. The east coast of America has a different sea level to its west coast. And as host Marnie Chesterton discovers in Finland, in some parts of the world the land is being pushed up, so sea level is actually falling. In fact, when nothing on earth - not the sea, the shore or the mountains - seems to be stable or constant, the question of what you measure from and to becomes incredibly tricky. But that hasn’t stopped oceanography and geography scientists risking life and fingers to use an ever-evolving array of technologies to find answers. In this show we find out why they care so much, and why we should too. Featuring: Dr Paul Bell – National Oceanography Centre, Liverpool, UK Dr Severine Fournier – NASA Jet Propulsion Laboratory / California Institute of Technology Dr Jani Särkkä – Finnish Meteorological Institute Khimlal Gautam – Mountaineer and Chief Survey Officer, Government of Nepal Dr Derek van Westrum – National Oceanic and Atmospheric Administration, USA Presented and produced by Marnie Chesterton Editor – Cathy Edwards Production Co-ordinator – Liz Tuohy Studio Manager – Steve Greenwood (Photo: Sea Level Elevation Sign in Death Valley, California. Credit: Mitch Diamond/Getty Images)