In 1990, the Intergovernmental Panel on Climate Change (IPCC) predicted that the average temperature on Earth would rise 0.3ºC per decade in the absence of international controls on greenhouse emissions. Let t measure the time in years since 1970, when the average global temperature was 15ºC. 

(a) Find a linear equation giving the average global temperature in degrees Celsius in terms of t, the number of years since 1970.

(b) Scientists have estimated that the sea level will rise by 65 cm if the average global temperature rises to 19ºC. According to your answer to part (a), when would this occur?

(c) A report from the IPCC in 2019 estimated the average temperature increase to be 0.2ºC per decade. Revise your answers to parts (a) and (b) using this new estimate.