If one day, the environment on the earth is no longer suitable for human habitation, what should we do?

If this deterioration continues, there are only two words left for mankind: extinction, because it is difficult for human beings to find a second earth in a short time, and even if they do, it is difficult to have the ability of interstellar migration in a short time! If your earth is not suitable for survival and human science and technology are developed enough, the last choice can only be to become an interstellar wanderer and travel in space in a super spaceship, hoping to really find a second earth!

So it depends more on when the earth became uninhabitable and the level of human scientific and technological development at that time! If human beings don't know how to cherish the earth's environment and destroy it unscrupulously, the earth itself will take revenge without waiting for the sun to "shoot". In the past 100 years, human beings have experienced the negative effects brought by the changes of the earth's environment, the power of nature and how insignificant human beings are in front of nature!

Sooner or later, the earth will not be suitable for human habitation, because even if the earth's own environment does not deteriorate, there will be a monster that will force the earth's environment to deteriorate. After billions of years, the sun will expand into a red giant, and the earth will be completely unfit for life!

To say the least, even if human beings have the ability of interstellar migration, the second earth is not so easy to find. Although the universe is very big, it is too difficult to find a planet like the earth. If you know the whole evolution history of the earth in detail, you will understand how perfect the earth is for human beings, almost tailored for life on earth. This is not surprising, because we were born on the earth! Anyway, protecting the earth's environment is the best and easiest choice. The earth is everything to us, and we have no reason not to love it!