The book is largely about climate change, but also includes some discussion of unregulated artificial intelligence and bioengineering, two other modern developments that in the author's view pose significant risks to humanity.

In a 2019 interview with Murtaza Hussain of The Intercept, McKibben claimed that at merely one degree Celsius of warming above pre-industrial levels, "[it] is already becoming difficult to live in large parts of the planet.

In detail, Bill McKibben explains how environmental factors such as pollution and ocean acidity are contributing to a decrease in the quality of human and natural life.

Criticism of right-wing politics and blame of the Koch Brothers and Donald Trump is prevalent, explaining how conservatism and libertarianism contribute to the climate epidemic.

In the ending of Falter McKibben transitions from the warnings of rapid human innovation, then provides reasons for hope, such as renewable energy advances (especially solar panels[3]) and climate activism.