What is the most significant action I can take to address our climate crisis?

People post this question when they become aware of the impending climate catastrophe.

Nature's hospitality to us humans (and by extension, the economic system) will not survive a government that is not in tune with the findings and recommendations of climate science,

The answer to the question is simple: 

Do everything that you can to elect leaders who implement science-based climate-policy. 

Scientists tell us that the Earth's hospitability cannot withstand going four years in the wrong ecological direction.

So vote for and encourage all others to vote for a healthy planet, regardless of political party or affiliation.