What is gigaton?

A gigaton is a unit of measurement used to describe the amount of carbon dioxide (CO2) emitted into the atmosphere by human activities, such as burning fossil fuels. One gigaton is equivalent to one billion metric tons. Gigatons are commonly used in discussions of climate change and efforts to reduce greenhouse gas emissions. The Intergovernmental Panel on Climate Change (IPCC) estimates that humans are currently emitting approximately 40 gigatons of CO2 per year, and that emissions must be reduced by at least 50% by 2030 to avoid catastrophic climate change.