USAAAO — 2021 First Round

Consider the following horrifying scenario. The Sun has become a Red Giant, and its radius is doubling every 100 years. Rank the following of humanity's concerns in order of immediate importance. I: Orbital decay due to direct contact between the Earth and Sun II: As the distance between the Earth and Sun shrinks, the Earth will enter the Sun's Roche limit and start to be ripped apart III: Orbital decay due to tidal effects on the Sun's outer atmosphere, the same way the Moon loses energy when forming the Earth's tides IV: Runaway greenhouse effect due to extreme temperatures, leading to the Earth becoming a hot, Venus-like planet with no habitability