Climate change has been occurring for a long time, but recent trends show that the average temperature in Central England has increased substantially over the past 350 years. Photographs of Muir Glacier in Alaska show it retreating over 20 km between 1941 and 2004. Maps of Bangladesh emphasize that large portions of the country are near sea level, making it vulnerable to sea level rise which could potentially displace tens of millions of people. Arctic sea ice cover has also significantly decreased between 1980 and 2007.