Skeptics of the potential of a rise in sea levels from global warming have pointed out that a melting of sea ice would not cause a rise in sea levels. For there to be a cause for concern about a rise in sea levels, they have argued, one would have to see a melting of the ice covering the land masses of Greenland and Antarctica. And previously, there had not been evidence of the melting ice sheet of Antarctica. In more recent years, however, there has been sudden dramatic evidence of the melting of the ice sheet covering Antarctica. This has included a cracking appearing across the main ice sheet and significant portions of the ice sheet of West Antarctica melting and breaking off.