New planet found in the constellation Perseus that has a dying, red giant star for a sun?

I recently read an article about a new planet found in the constellation Perseus that has a dying, red giant star for a sun. The article talked about how the red giant was expanding as it dies, and will eventually consume the planet as it moves ever so closer in proximity. My question is related to this event. The article said our sun is a red dwaft and will expand and comsume earth within the next 5 billion years. It states that in 2 billion years earth's seas will be boiling water. So, is it logical to ume that global warming could also be influenced, or the result of, the sun's expansion towards earth? Dividing 2 billion years by 93 million miles (astronomical unit) gives an average yearly closure of 21 miles. Could be average temperature change per year on earth be positively correlated with a mere 21 miles expansion per year by our sun? Also, what would be the resulting calculation of temperature change per year if that 21 miles were the only factor in earth's temperature change, disregarding global warming?