
I said the Earth's mass tiny compared to the Sun's, so any mass change of the earth will have no negligible effect on the orbit, as it's the Sun's gravity, not the earth's that keeps us going round the Sun. Changing the mass of the Sun will therefore effect the earths orbit, as the gravity of the sun is proportional to its mass. (another example is say if you drop a hammer and a feather in a vacuum, they both hit the ground the same time, as although they have different masses, the difference between them is negligible in comparison to the size of the earth).
The Sun makes up 99.8% of the mass in our solar system. Add the planets, and there's not a lot left, so it isn't going to get any bigger yet... It is however getting smaller as it burns up, and in about a billion years, the sun will be 10% hotter, and in 3.5 billion years, the oceans on earth will boil and it will be too hot to live on. A bit later than that maybe 7 billion years from now, the sun will become a red giant, and will swallow mercury, and will scorch earth and venus, but won't consume them because it's mass will decrease and they will move away from it due to the decreased gravity. Now there's global warming for you, but I don't think I'll be caring about it

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We don't.