evidence: Human emissions of greenhouse gases are the primary driver of climate change today.1 CO2 and other greenhouse gases like methane and nitrous oxide are emitted when we burn fossil fuels, produce materials such as steel, cement, and plastics, and grow the food we eat. If we want to reduce these emissions, we need to transform our energy systems, industries, and food systems. [...] How much CO2 can the world emit while keeping warming below 1.5°C and 2°C?