Road traffic and residential heating are the two main sources of CO₂ emissions in many cities. HeiGIT´s new emission inventories map these emissions and can simulate the effects of new policies and interventions. We calculated how emissions would change in Heidelberg, Germany, if we introduced a 30 km/h road speed limit and replaced oil and coal heaters with heat pumps.
Introduction
It is urgent to reduce CO₂ emissions. To achieve this, we need to know how much we emit, where, when, and why (i.e., an accurate, high-resolution emissions inventory). Such knowledge allows us to target our emission reduction efforts, e.g. by identifying the biggest emission sources, and to track our progress.
Researchers at HeiGIT are developing a tool based on open data to construct high-resolution bottom-up emission inventories in cities around the world. In addition to identifying priorities and monitoring trends, these tools can be used to simulate the emission reductions resulting from particular policies or interventions.
We started by modelling the two main sources of urban CO₂ emissions in Heidelberg, Germany: Road traffic and residential heating.
Road traffic emissions
We estimated road traffic CO₂ emissions using a traffic model based on open data. To estimate the traffic volume on each road, we accounted for the type of road – distinguishing between, for example, highways and residential roads – and their number of lanes (using information from OpenStreetMap), as well as for population density (with data from the Global Human Settlement Layer). We then calculated road traffic CO₂ emissions by multiplying the traffic volume by emission factors accounting for driving speed and the composition of the German vehicle fleet.
With our approach, we can simulate how changes in the parameters would influence road traffic CO₂ emissions. For example, it is often discussed to reduce the speed limit in cities to increase safety and reduce noise as well as air pollution. We simulated a reduction of the speed limit on all inner city roads in Heidelberg to 30 km/h. Since our driving speed-dependent emission factors assume a higher fuel consumption and thus also higher emissions at lower speeds, the emissions in Heidelberg increased by about 4% in the scenario. However, a study by the German Federal Environment Agency has shown that a reduction of the speed limit on main roads in cities may reduce the amount of traffic, on the one hand because the capacity of roads decreases at lower speeds, on the other hand because lower driving speeds make other modes of transport such as cycling more attractive. This effect is not included in our simulation. If only 37 trips per day in Heidelberg were done on foot or by bike instead of using cars, this would already make up for the emission increase in our scenario. It is possible that the effect of the reduction of traffic would be stronger than the effect of the higher fuel consumption at lower speeds, so that the overall traffic emissions would decrease. Another limitation of our model is that acceleration is not included. While higher fuel consumption at lower speed applies to steady-state driving, a lower speed limit could entail less acceleration and thus also lead to an overall decrease of emissions.
Daily road traffic CO₂ emissions [t/road-km] in Heidelberg for regular and reduced speed scenario. Many of the major roads inside the city show slightly higher emissions in the reduced speed scenario.
Heating emissions
In Germany and other countries with temperate climates, keeping our homes warm during the cold season is one of the main sources of CO2 emissions. Most households in Germany are still heated by burning fossil fuels. In the city of Heidelberg, 57.1% of residential buildings use natural gas for heating, while 12.1 % use oil and 0.3% use coal.
Besides the type of energy we use to heat our homes, other important factors for heating emissions are the total area that we heat (for example, heating only the rooms where we spend most time can help to sharply reduce energy consumption and the associated emissions) and how well thermally insulated buildings are (which determines how much energy we need to maintain a certain temperature).
We used data from the 2022 German census to estimate CO2 emissions from space heating in residential buildings. The census includes gridded data (at a 100-m resolution) of key factors determining heating emissions: population counts, average living space per capita, building age, and the energy carriers for heating (i.e., whether buildings are heated with fossil gas, oil, coal, wood, heat pumps, etc.). By combining this information with heating energy consumption rates for buildings of different ages (i.e., newer buildings tend to be better insulated and use less energy) and emission factors for different energy carriers, we can estimate the emissions from heating residential buildings in any area of interest within Germany.
We can also quantify the emission reductions achievable with particular interventions. For example, if all the households in Heidelberg that still heat with oil and coal, two of the dirtiest fuels, installed heat pumps instead, residential heating emissions in the city would fall by nearly a fifth (17.6%). This refers only to the carbon dioxide emitted directly from residential buildings. The emissions resulting from electricity generation to power the heat pumps is not included in these calculations yet.
Future steps
In the future, we plan to expand our emission inventory to other sectors, such as commercial buildings, industry, and waste management. Additionally, we will explore options to include indirect emissions from electricity consumption, as well as upstream emissions of consumed goods and services. e.g. from their production, transportation, and distribution.
Together with other indicators related to climate action, our emission inventory will be publicly available in an online dashboard later this year.
As we continue to improve and expand these inventories, we welcome feedback from experts and the broader academic and climate action communities. We also invite city administrations and any other organization interested in a detailed analysis of your city or area to contact our Community Engagement Manager for Climate Action Kirsten von Elverfeldt (kirsten.vonelverfeldt@heigit.org).
To keep up with future developments and releases related to this project as well as other efforts to advance geospatial technology in the mobility, humanitarian aid, and data analytics space, follow our social media channels and stay up to date on our blog.