The amount of carbon dioxide that we can still emit while limiting global warming to a given target is called the “remaining carbon budget,” and it has become a powerful tool to inform climate policy goals and track progress towards net-zero emissions targets.
This carbon budget is like a fixed financial budget: there is a cap on total allowable expenses over time, and excess spending in the near term requires deceased spending in the future.
Similarly, the remaining carbon budget is a fixed total quantity of future emissions that is small enough to limit global temperature increases before they exceed our climate targets. Scientists’ estimates of the remaining carbon budget vary widely.
Studies often use different approaches or even definitions of what the carbon budget represents. This can involve different treatment of how greenhouse gases other than CO2 contribute to climate change, or the incomplete representation of some processes, such as the role of aerosols in climate change.
The large range of estimates can be used either to write off ambitious climate targets or argue that the transition to a low-carbon economy can proceed gradually over several decades. Neither extreme reflects the actual uncertainty especially well.
We developed a new way to generate a better estimate of the remaining carbon budget for the 1.5C limit of the Paris Agreement that integrates all major sources of uncertainty. Our results suggest that even if the growing list of countries committing to 2050 net-zero emissions targets reached their goals, we would still deplete the 1.5C remaining carbon budget more than a decade too soon. This is a stark reminder of how quickly we are running out of time to achieve the most ambitious temperature goal of the Paris Agreement.
Our best estimate of the 1.5C remaining carbon budget is 440 billion tonnes of CO2 from 2020 onward. If human activities around the globe continue to produce CO2 at current rates, we will deplete the remaining carbon budget in a little more than 10 years. If we slow our rate of emissions, the remaining budget will last longer.
To avoid exceeding the remaining carbon budget, we need to stop emitting CO2 altogether. A budget of 440 billion tonnes from 2020 means that global CO2 emissions need to decrease to net-zero by about 2040. However, even this would give us only a 50 percent chance of not exceeding 1.5C. For a 67 percent chance, total CO2 emissions must not exceed 230 billion tonnes. This is about five years of current emissions or reaching net-zero emissions by 2030.
The Daily Times