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Since the start in 2018, we have released several editions of Climate Call. These editions include partially different sets of cards. Detailed explanations for calculations are available only for the cards in the latest edition of the card game, published in 2024. How do you know if you have the latest edition? Check the card box! The latest edition is labeled “2024” on the side of the box.

If you have the latest edition and compare it to cards from previous editions, you’ll notice that the numbers on some cards differ. There are several reasons for this.

In particular, we have included the so-called high-altitude effect for flights, which has led to increased emissions for all flights over 500 km. Secondly, we have rounded all figures to two significant digits and the nearest multiple of five, departing from a less precise rounding approach we used previously. Last but not least, we have updated the calculation model with some new data and corrected some minor errors that were discovered.

In summary, the emission values in the latest edition are more up-to-date and accurate than before. We do not recommend mixing cards from different editions as they are not entirely comparable. 

Enhanced Climate Impact Due to High-Altitude Emissions

Airplanes flying at high altitudes cause both a direct impact on the climate in the form of carbon dioxide emissions from fuel combustion and indirect effects linked to emissions at high altitudes. The indirect effects include a warming effect due to high-altitude cloud formation (water vapor being a potent greenhouse gas) and a cooling effect due to emissions of particles that reflect incoming solar radiation back into space.

Because these effects are challenging to estimate and counteract each other, previous editions of the game considered only the direct climate impact from fuel combustion. However, thanks to new climate research published in 2021 (Lee et al., 2021), and greater consensus among researchers regarding the net effect, we have included the so-called high-altitude effect (also called non-CO2 effects) in the latest edition of Climate Call. 

How much the climate impact is amplified depends on the altitude at which the emissions occur, which in turn depends on the distance flown (the longer the distance, the higher up in the atmosphere the aircraft flies). We have considered an enhancement factor of 0% for flights under 500 km, 70% for all flights over 1000 km, and a linear increase of the enhancement factor from 0% to 70% for all flights between 500 and 1000 km.

The inclusion of the high-altitude effect means that all longer flights have higher emissions in the latest edition of Climate Call from 2024. This also affects cards related to air freight.