The world needs to reach net-zero emissions — a balancing point where the amount of greenhouse gases emitted into the atmosphere is equal to the amount removed — by around 2050 to limit warming to 1.5 degrees Celsius (2.7 degrees Fahrenheit) and avoid rapidly worsening climate impacts. More than 100 countries, covering more than 80 percent of global greenhouse gas emissions, have already set have a net-zero target.

Actions to cut emissions, such as scaling up clean energy or switching to electric vehicles, can get us most of the way to net zero. But they won’t get us all the way. Some emissions will very likely be leftover by midcentury, whether because the technology to eliminate them doesn’t exist, isn’t widely available or can’t be deployed quickly enough. These remaining or “residual” emissions will need to be balanced out with an equal amount of carbon dioxide removal — the “net” part of net zero.

While the concept of residual emissions seems