year,mean_alt
2000,131.2899858
2001,131.8845278
2002,128.5770833
2003,141.2561494
2004,144.9606207
2005,146.8926049
2006,146.6611552
2007,146.6275578
2008,139.895161
2009,135.1224755
2010,141.922992
2011,144.6245072
2012,144.3332782
2013,142.5943316
2014,143.4435493
2015,146.2287039
2016,147.3374653
2017,145.3409937
2018,146.1562941