Analysis of satellite data indicates that the Greenland ice sheet lost approximately 2900 gigatons (gt) of mass between March 2002 and September 2014. The mean mass loss rate for 2013–14 was 6 gt/year; the rate for 2012–13 was 474 gt/year.

(a) What derivative does this tell us about? Define the function and give units for each variable.

(b) What numerical statement can you make about the derivative? Give units.