The CO₂ Cube

The dice has dropped

How big is a ton of CO2? And what does this ton stand for? A joint project by Wiener Stadtwerke and the Vienna Ball of Sciences illustrates the volume of such an amount of carbon dioxide – and the dimension of the challenge of making Vienna a CO2-neutral metropolis by 2040.

It all started with a simple question: How big is a ton of CO2? The role of CO2 in global warming is now widely recognized. Although CO2 makes up a small proportion of the air, only around 0.038 percent. However, in its function as a greenhouse gas, it plays a crucial role in our climate: CO2 absorbs part of the heat given off by the Earth into space and radiates it back to the Earth.

Around 87 percent of greenhouse gas releases come from carbon dioxide, 6.5 percent from methane and 4.5 percent from nitrous oxide. In order to understand the scale, these quantities are often given in the form of tonnes: in 2021, greenhouse gas emissions per capita in the EU amounted to an average of 7.8 tonnes of so-called CO2 equivalents. In Austria, emissions per capita were 8.7 tonnes in 2021 – and therefore higher than the value for the EU-27.

So how big is a ton? A random private survey in the Science Ball team’s environment resulted in estimates of cube dimensions between 30 cm and 13 meters. In fact, it is a cube with each side length of around 8 meters. Jeroen Dobbelaere, ISTA’s sustainability officer, made the calculation: At standard pressure and an air temperature of 15 °C, the density of carbon dioxide is 1.87 kg/m3. One ton of carbon dioxide fills 534.8 cubic meters, which in turn corresponds to a cube with an edge length of 8.12 meters.

Given that we constantly use this size of one ton as the key currency for climate change, the idea of it is quite vague. That was the starting point of the conversation with Peter Weinelt, General Director of Wiener Stadtwerke since the beginning of 2024. The result is the cube, which illustrates one ton of CO2, and can be admired for the first time at the Vienna Ball of Sciences in the arcade courtyard of the town hall. On the occasion of the 75th anniversary of the municipal utility in 2024, the cube will make further appearances. The company plays a key role in realizing the goal of making Vienna a CO2-neutral metropolis by 2040 – in other words: decarbonizing the federal capital’s energy supply.

The decarbonization study of the municipal utilities:

You can read the full text in the 2024 ball magazine, which will be published on the evening of the ball.