One frequently quoted study of the global costs of mitigating climate change put them at around $3 trillion by 2100, with the main benefits being felt between 2100 and 2200. Here is alternative way to spend around the same amount of money with around the same timescale of payback: terraforming Mars. A standard estimate is that, for about $2-$3 trillion, in between 100 and 200 years we would be able to get Mars from its current “red planet” (dead planet) status to ” blue planet” (i.e. a dense enough atmosphere and high enough temperature for Martian water in the poles and soil to melt, creating seas) – achievable in about 100 years – and from there to microbes and algae getting us to “green planet” status within 200 to 600 years.