One of the major indicators of global climate change is thought to be the rapid Arctic sea ice loss, or the opening of the sea ice above the Arctic Circle to the North Pole. Although no one knows when the area will be an ice-free Arctic summer, several theories exist. The first is based on observed sea ice trends—how the ice has decreased rapidly over the previous decade. Using these trends, it appears the area will be ice-free by 2020. Another theory is based on the assumption that in the future multiple, but random in time, large sea ice loss events will occur, as happened in 2007 and 2012. Using this idea, it is estimated that the area will be ice-free by 2030. And yet another theory is based on computer models, using not only sea ice date, but other factors of the climate, such as ocean, land, atmosphere (especially the amount of greenhouse gases), and ice conditions in the past. Most of these models estimate that the area would be ice-free by 2060. Whatever theory a person ascribes to, the reality is that almost all scientists who study such sea ice changes believe the Arctic will be ice-free within the next fifty years.