Recent studies indicate that the average surface temperature of the earth has been rising steadily. Some scientists have modeled the temperature by the linear function $T=0.02 t+8.50$, where $T$ is temperature in ${ }^{\circ} \mathrm{C}$ and $t$ represents years since 1900 .
(a) What do the slope and $T$ -intercept represent?
(b) Use the equation to predict the earth's average surface temperature in 2100 .