“Impossible to see, the future is,” says wise Yedi-Master Yoda in George Lucas’ science fiction epic Star Wars.

But ever since scientists used punch cards to create the first climate models of the atmosphere in the 1960s, humanity has been able to get a glimpse of possible temperature scenarios on our planet. It was then when we realized: The future is not looking good, and the planet is rapidly heating up at a faster pace than we expected. This is the result of an analysis of several climate models, performed by the World Meteorological Organization (WMO). By 2026, earth could already be 1.5 °C warmer compared to 1850. But how did scientists come across this finding in the first place? How does a climate model work and why are they so important?

Climate modelling is incredibly complex due to the literate nature of its research subject: nature, Earth, and its climate. In order to break down its complexity, climate models run on a basic principle. The world’s climate is divided into grid squares to be able to calculate each regional climate more easily. This procedure already dates back as early as the First World War, when the Brit Lewis Richardson used it in an attempt to predict the weather.

The fathers of climate modelling, Syukuro Manabe and Richard Wetherald, applied the same procedure when they programmed their first realistic climate model at Princeton University in the 1960s. Their model’s code fit on a single punch card, the 270-year-old predecessor of the USB stick, used to transfer data mechanically into a computer. The climate models being used for the WMO´s prediction still employ Lewis’ grid square system, only now it is three-dimensional and virtual. The models usually contain enough computer code to fill almost a million punch cards, while they require supercomputers the size of a soccer field to run.

But how do scientists know whether their calculations are correct?

On the one hand, climate modelers compare their calculations with each other. This is predominantly done at conferences or in scientific journals in a process called peer-review. If calculations are not sound, they will not be pursued.

On the other hand, many models are open source based, meaning that anyone can download the code from the internet, and then correct it or make suggestions to further improve the model, which is intended to promote transparency and collaboration. At the same time, the calculations are cross-checked with historical temperature data.

Based on diverse and extensive models, different strands of knowledge can be combined. This allows humanity to explore how human development and societal choices interact with and ultimately drive our climate. It is because of those models that, with the current political measures in place, we understand that there is a probability the world is heading towards 3.2°C global warming by 2100 with dire consequences for planet earth and humanity.

To make predictions like these or to give a global temperature forecast of 2026, as recently released by the WMO, an enormous amount of brain-, calculating- and financial power is needed. Hundreds of experts from different scientific fields like oceanology, atmospheric science, or cloud specialists work on a single model that will need years to build and improve. A myriad of calculations and interactions within the system require enormous computing power. The computers used roughly calculate three trillion calculations – per second. Climate modelling is thus very costly and energy intensive, which is why big research institutes in the global North usually run the bulk of those models. Others can be found in Asia, South America, and Australia.

Climate models build the knowledge foundation on which policy decisions on an international scale are made. It is because of those models that we have numeric proof that global warming is being accelerated by human activities. They allow us to counter-calculate and take stock where we stand in curbing the climate crisis, as we can put a number on probable temperature rise on the political climate efforts. Thanks to models, we can estimate how quickly, how much, and where to cut CO2 to keep the earth in a liveable condition. This is why the predictions scientists provide based on computer technology, have become irreplaceable as a basis for decision-making today.

Humanity heavily relies on models to make assumptions about the future, because – as the physicians Knutson and Tuleya once phrased it sarcastically – “observations of the future are not available at this time.” Even with modern high-performance computers and enormous scientific efforts, humanity has not yet fully understood the complex interactions of system earth, but climate models are probably the tool that comes closest to “seeing the future”. What we do with this information is up to us.