Exercise 3 solution

At 3.7 mm/yr for 30 years: 3.7 x 30 = 111 mm, about 11 cm.
At 4.5 mm/yr for 30 years: 4.5 x 30 = 135 mm, about 13.5 cm.

A steady rate is a poor assumption because both causes can speed up. Thermal expansion continues as long as the ocean takes up heat, and the heat reaches deeper layers over decades. Melting of glaciers and the Greenland and Antarctic ice sheets can accelerate as warming continues and as ice loses its support or its cold surface, and the ice loss adds water faster than a straight line would predict. Planning therefore uses ranges for different scenarios, and local figures must also allow for land rising or sinking.