Please answer a question about the following article about Tuvalu:

Whether there are measurable changes in the sea level relative to the islands of Tuvalu is a contentious issue. There were problems associated with the pre-1993 sea level records from Funafuti which resulted in improvements in the recording technology to provide more reliable data for analysis. The degree of uncertainty as to estimates of sea level change relative to the islands of Tuvalu was reflected in the conclusions made in 2002 from the available data. The 2011 report of the Pacific Climate Change Science Program published by the Australian Government, concludes: "The sea-level rise near Tuvalu measured by satellite altimeters since 1993 is about 5 mm (0.2 in) per year."

What subject is arguable concerning Tuvalu?
sea level