Sea level rise has been estimated to be on average between + and per year ± since 1993. Additionally, sea level rise has accelerated in recent years. For the period between 1870 and 2004, global average sea levels are estimated to have risen a total of , and ± per year, with a significant acceleration of sea-level rise of ± per year per year. According to one study of measurements available from 1950 to 2009, these measurements show an average annual rise in sea level of ± per year during this period, with satellite data showing a rise of ± per year from 1993 to 2009. Sea level rise is one of several lines of evidence that support the view that the global climate has recently warmed. In 2014 the USGCRP National Climate Assessment projected that by the year 2100, the average sea level rise will have been between one and four feet (300mm-1200mm) since the date of the 2014 assessment. Current rates of sea level rise have roughly doubled since the pre 1992 rates of sea level rise of the 20th century.