A carbon budget represents the maximum amount of carbon dioxide (CO2) that can be released into the atmosphere while still limiting global warming to a specific temperature target. This concept is central to international efforts to mitigate climate change, quantifying the remaining allowable emissions to prevent severe impacts. It serves as a scientific benchmark, guiding policy decisions and global actions to reduce greenhouse gas emissions.
Understanding the Carbon Budget
The concept of a carbon budget is rooted in the scientific understanding that global temperature rise is directly proportional to the total, or cumulative, CO2 emissions released into the atmosphere by human activities. This near-linear relationship means that to stabilize global warming at any particular level, global CO2 emissions must eventually reach net zero. Scientific bodies, such as the Intergovernmental Panel on Climate Change (IPCC), determine these budgets by combining knowledge about past warming, the amount of warming per cumulative ton of CO2, and the expected warming even after emissions cease.
The IPCC established the carbon budget as a central concept for climate policymaking. For example, to limit global warming to 1.5°C above pre-industrial levels, the remaining carbon budget from January 1, 2020, was estimated at 400 billion tonnes of CO2. These calculations consider that other greenhouse gases also contribute to warming, further influencing the overall budget.
The Urgency of the Carbon Budget
The carbon budget underscores the pressing need for action, as exceeding it carries severe consequences for the planet. Every additional emission contributes to further warming, making the need for action immediate.
Exceeding the carbon budget leads to an increased frequency and intensity of extreme weather events, such as heatwaves, droughts, wildfires, and extreme rainfall. It also contributes to sea-level rise and widespread ecosystem disruption. Staying within the budget is necessary for avoiding the most severe impacts of climate change and managing associated risks. The IPCC’s Sixth Assessment Report found that human emissions have already warmed the climate by nearly 1.1 degrees Celsius since 1850-1900, with the global average temperature expected to reach or exceed 1.5 degrees Celsius within the next few decades.
The Remaining Carbon Budget
The remaining carbon budget for limiting warming to 1.5°C is small and shrinking rapidly with ongoing emissions. As of early 2025, the central estimate for the 1.5°C target is approximately 130 billion tonnes of CO2. At current emission rates, this budget could be exhausted in as little as three years. The 2024 Global Carbon Budget projects total CO2 emissions to be around 41.6 billion tonnes, indicating no sign of a peak in fossil CO2 emissions.
If the carbon budget is exceeded, it leads to a temporary “overshoot” of the temperature target. This means temperatures would temporarily rise above the desired limit, requiring future large-scale deployment of carbon dioxide removal (CDR) technologies to bring them back down. Relying on overshoot scenarios carries significant risks, including potentially irreversible consequences like increased sea-level rise and impacts on frozen ecosystems such as permafrost. Such scenarios also expose more people to climate extremes and increase the risk of crossing climate tipping points.
Pathways to Meeting the Carbon Budget
Meeting the remaining carbon budget requires a multifaceted approach, primarily involving rapid and significant reductions in greenhouse gas emissions across all sectors. This includes transitioning to renewable energy sources like solar, wind, and geothermal, which can significantly lower reliance on fossil fuels. Boosting energy efficiency in homes, industries, and transportation, through measures like choosing energy-efficient appliances and improving fuel efficiency in vehicles, is also a substantial pathway.
Beyond emission reductions, carbon dioxide removal (CDR) technologies play a complementary role. These strategies aim to remove CO2 directly from the atmosphere, encompassing natural approaches like reforestation and afforestation, which utilize trees to absorb carbon. Technological solutions, such as direct air capture, which scrubs CO2 from the air for sequestration, and bioenergy with carbon capture and storage (BECCS), are also being developed. International cooperation, strong policy frameworks, and continuous technological innovation are all necessary to achieve the scale of change required to stay within the global carbon budget.