Thanks to the newest addition to the Climate Action Navigator, it is now possible to calculate the remaining CO₂ budget for several German cities (Berlin, Bonn, Hamburg, Heidelberg, and Karlsruhe) to stay within certain global warming limits (e.g. +1,5°C). The CO₂ Budget assessment tool also tracks if the city is on the right track to stay within this budget.
CO₂ Budgets: How Much Carbon Can a City Emit Before Exceeding its Climate Target?
A CO₂ budget shows how much CO₂ a city or country is allowed to emit in order to limit global warming to a certain target.
The Paris Climate Agreement, which was adopted in 2015, is a key reference to calculate the target. In this agreement, many countries have committed to limiting global warming to well below 2°C compared to the time before industrialization, while striving to limit global warming to 1.5°C. To achieve these goals, it can be of great help to define targets on a local level, highlighting the role of each country or even city in limiting emissions.
Based on the Paris Climate Agreement, we can calculate how much CO₂ a particular city can still emit while doing its part to limit global warming. This amount is the city´s CO₂ budget. With the CO₂ Budget assessment tool on our Climate Action Navigator, we have calculated the CO₂ budget of the German cities of Berlin, Bonn, Hamburg, Heidelberg, and Karlsruhe.
As most cities have already used up their CO₂ budget for 1,5°C or 1,7°C, or are on the path of using it up very soon, the Climate Action Navigator calculates also CO₂ reduction paths that complies with a 2°C temperature limit. It should be noted that the Paris Agreement stipulates a limit of well below 2°C temperature increase.
The CO₂ budgets do not imply that temperature limits will automatically be met if a city complies with its budget. In order to ensure that the global warming limits are not exceeded, the whole world needs to comply with its CO₂ budget.
Visualizing CO₂ Budgets
The CO₂ Budget assessment tool calculates the CO₂ budget of a city based on how much carbon the city “is allowed” to emit without exceeding the limits posed by the Paris Agreement. It subtracts the amount of CO₂ that has already been spent (according to CO2 emissions reported by the cities) to determine how much CO₂ still remains in the budget. The tool then uses future emission projections to predict when the CO₂ budget will be used up. These emission projections are based not only on current emissions, but also on planned policies, taking into account emission reduction measures currently planned by the city.
On the Climate Action Navigator dashboard, users can compare the projected emission reduction path of the city to the reduction paths that would be necessary to limit global warming to 1.7°C and 2°C, respectively.
It is also possible to visualize the difference between the total projected emissions of the city and its CO2 budget. This way, the user can quickly see whether the city is on the right track to stay within the global warming limits.
While the tool is currently limited to a few cities in Germany, we plan to expand it to further cities in the future.
Berlin CO₂ Budget
At the time the Paris Agreement was signed, the city of Berlin had a remaining CO₂ budget of 136,7 million tons to do its part to stay within a global temperature increase of 1,5°C. It is estimated that at least 125 million tons have already been emitted since then (data from 2023).
Based on current projections, the city´s emissions have already exceeded the calculated CO₂ budget to stay within an increase of 1,5 °C. To avoid exceeding the limit of +1,7°C in global warming, Berlin should cut its emissions to zero by 2040. Based on our projection, the city is estimated to reach net zero emissions around 2040.
More insights on Berlin´s CO₂ budget can be found in the Climate Action Navigator.
Bonn CO₂ Budget
At the time the Paris Agreement was signed, the city of Bonn had a remaining CO₂ budget of 12,1 million tons to do its part to stay within a global temperature increase of 1,5°C. It is estimated that at least 14 million tons have already been emitted since then (data from 2022).
The city´s emissions have already exceeded the calculated CO₂ budget to stay within an increase of 1,5 °C. To avoid exceeding the limit of +1,7°C in global warming, Bonn should cut its emissions to zero by 2040. With the emission reduction measures currently implemented or planned, the city is estimated to reduce its emissions substantially by 2035, putting it on a good pathway to reach net zero emissions around 2040.
More insights on Bonn´s CO₂ budget can be found in the Climate Action Navigator.
Hamburg CO₂ Budget
At the time the Paris Agreement was signed, the city of Hamburg had a remaining CO₂ budget of 67,2 million tons to do its part to stay within a global temperature increase of 1,5°C. It is estimated that at least 100 million tons have already been emitted since then (data from 2023).
The city´s emissions have already exceeded the calculated CO₂ budget to stay within an increase of 1,5 °C. To avoid exceeding the limit of +1,7°C in global warming, Hamburg should drastically cut its emissions by 2030 and reach zero emissions by 2040. Based on our projection, the city´s emissions will largely surpass the budget for +2°C by 2040, if no additional emission reduction measures are put in place.
More insights on Hamburg´s CO₂ budget can be found in the Climate Action Navigator.
Heidelberg CO₂ Budget
At the time the Paris Agreement was signed, the city of Heidelberg had a remaining CO₂ budget of 5,8 million tons to do its part to stay within a global temperature increase of 1,5°C. It is estimated that at least 7 million tons have already been emitted since then (data from 2022).
The city´s emissions have already exceeded the calculated CO₂ budget to stay within an increase of 1,5 °C. To avoid exceeding the limit of +1,7°C in global warming, Heidelberg should cut its emissions to zero by 2040. With the emission reduction measures currently implemented or planned, the city is estimated to reach net zero emissions around 2068.
More insights on Heidelberg´s CO₂ budget can be found in the Climate Action Navigator.
Karlsruhe CO₂ Budget
At the time the Paris Agreement was signed, the city of Karlsruhe had a remaining CO₂ budget of 11,0 million tons to do its part to stay within a global temperature increase of 1,5°C. It is estimated that at least 16 million tons have already been emitted since then (data from 2019).
The city´s emissions have already exceeded the calculated CO₂ budget to stay within an increase of 1,5 °C. To avoid exceeding the limit of +1,7°C in global warming, Karlsruhe should drastically cut its emissions by 2035 and reach zero emissions by 2040. Based on our projection, the city´s emissions will largely surpass the budget for +2°C by 2040, if no additional emission reduction measures are put in place.
More insights on Karlsruhe´s CO₂ budget can be found in the Climate Action Navigator.
From Insight to Action: the Climate Action Navigator
The Climate Action Navigator is more than just a dashboard to assess climate mitigation measures in cities worldwide. It aims to identify local strengths, highlight areas for improvement, and support the development of targeted solutions to make cities more livable, inclusive, and climate-resilient. Unlike traditional indices, the CAN assessment tools are co-created with urban planners, advocacy groups, and local stakeholders to ensure practical and actionable results.
More information on the Climate Action Navigator and its assessment tools can be found on the project webpage and on our blog.
