A biofuel is any fuel made from plants or animals. The raw material—or biomass—is commonly corn, sugarcane, wood pulp, or beets. Fermented sugars create alcohol, such as ethanol, which derives from corn. Gates discusses biofuels as a substitute for fossil fuels (like oil and coal), which result over time from geological processes and release carbon when we burn them.

Gates refers to this organization often throughout the book. It began as the Breakthrough Energy Coalition at the 2015 United Nations Climate Change Conference in Paris. At the request of François Hollande, the president of France at that time, Gates recruited a group of private investors to complement the work of the participating governments, all of which wanted to back technologies to reach the goal of zero emissions by 2050. The organization’s website address is breakthroughenergy.org.

Various gases create the greenhouse effect that is warming the planet and that we thus call greenhouse gases. Of these gases, the most well-known is carbon dioxide (CO2); others include methane and nitrous oxide. The heat they give off varies, so calculations sometimes involve a comparable unit, or carbon dioxide equivalent (CO2e).