They say warmer conditions are encouraging algae to grow and darken the surface. Dark ice absorbs more solar radiation than clean white ice so warms up and melts more rapidly. Currently the Greenland ice sheet is adding up to 1mm a year to the rise in the global average level of the oceans. It is the largest mass of ice in the northern hemisphere covering an area about seven times the size of the United Kingdom and reaching up to 3km (2 miles) in thickness. This means that the average sea level would rise around the world by about seven metres, more than 20ft, if it all melted.
