Quoting Vice's source: "The analyzed records have an average twentieth century rate of approximately 1.6 mm/yr, but based on the locations of these gauges, we show that the simple average underestimates the twentieth century global mean rate by 0.1 ± 0.2 mm/yr."
The old number had a margin of error too. It's not strange, just a sign of thorough math.
What they say is approximately "1.5-1.9 with values near 1.7 being most likely", so in layspeak and round numbers, the chance that actual number is higher is 90% and that it's lower is 10%.
