Answer
a) The slope represents the rate of average surface temperature increase of the Earth. The T-intercept represents the average surface temperature of the Earth in 1900.
b) 12.5$^{\circ}$C
Work Step by Step
a) The slope measures $\frac{\Delta T}{\Delta t}$, the change in temperature over time or the rate of temperature change. The T-intercept represents the temperature when $t=0$, defined as the temperature 0 years since 1900.
b) at $t=2100-1900=200, T=0.02\times200+8.50=12.5^{\circ}$C
