From the
Wall Street Journal's blog, titled "Gary Johnson Calls for Human Settlement of Other Planets", explains the need for humanity to settle on other planets:
Candidates often discuss their plans for their first day in office, but rarely the future of the human race billions of years after their presidency.
“We do have to inhabit other planets,” Gary Johnson, the Libertarian Party presidential candidate said in an interview on ABC’s “This Week” on Sunday. “The future of the human race is space exploration.”
Mr. Johnson was questioned on the topic because he had once said he opposed certain programs to mitigate climate change because “the long-term view is that in billions of years, the sun is going to actually grow and encompass the earth.”
Mr. Johnson said the 2011 remarks were humorous and that he supports both space exploration and a role for environmental regulation.
“We should be prudent with the environment,” Mr. Johnson said, “The EPA exists to protect us against individuals, groups, corporations that would do us harm. Pollution is harm.”
In fact, private space companies, such as SpaceX, has undertaken such. The Interplanetary Transport System, formerly known as the Mars Colonial Transporter, is due to be revealed this month.
EDIT: We can perhaps escape from Earth in any event of something happens to prevent any manned space program from being realized, I mean, there's a looming probability of a Donald Trump presidency. There could be World War III, where any conventional conflict goes nuclear very rapidly, and/or there's social movements that's anti-technology, anti-science, and anti-modern, such as Putinism and Dugin's Eurasianism, which calls for humanity to be "rooted in the soil" without "individual rights" and "technological progress".
EDIT #2: There are habitable exoplanets, the nearest discovered is Proxima b. I bet that humanity will get there in the future.