Greta Thunberg argues that climate change is the most significant threat humans have ever faced, but humanity has denied, ignored, and politicized the crisis. The boundary between sustainable and unsustainable is absolute: “It is like walking on thin ice—either it carried your weight, or it does not” (2). To prevent a climate crisis, humanity needs to drastically change. The Climate Book, which is a collection of essays with over 100 contributing voices, is intended to increase public awareness about the facts of climate change.

Thunberg observes that people must understand climate change before they can take efficient actions against it. Hope is important, but Thunberg questions whether hope is preventing people from acting. Several countries manipulate how they report their carbon dioxide (CO₂) emissions, making it look as if their emissions are declining while global emissions are rising. Emissions need to drop to 1 tonne per person per year to be sustainable. This is not a problem for most humans, as they live in pre-industrial settings. Most emissions come from the industrialized Global North.

Thunberg encourages people to make an impact by joining the fight, and she stresses the importance of a democratic approach.