Text written in Basque and translated automatically by Elia without any subsequent editing. SEE ORIGINAL

The problem of being more pessimistic than necessary

We are changing the climate, it is clear, and it will bring serious problems. But it is important to make the most realistic prediction possible. The climatologists have officially said: RCP8.5 is no longer a reasonable scenario. Nor the subsequent SSP5-8.5 scenario. There are many reasons for this, especially that it does not coincide with the trend of emissions that are being observed.

We are talking about the evolution of the climate. Scientists don’t just study the past and the present. In addition, they make predictions to try to understand where we are going in the future. And instead of calculating the only possible future, they propose the scenarios. That is, several possible futures, from the most optimistic to the most pessimistic.

But in recent years many experts have questioned whether the two extreme scenarios are realistic, and now the news is official. The most optimistic scenario is the RCP1.9 scenario, which defends a 1.9 °C increase in atmospheric temperature in 2,100 years. There is a great consensus that this milestone will be overcome by then. The most pessimistic (RCP8.5) predicts a warming of 8.5°C at the end of the century. The latter has been questioned by experts since 2020. Many of the scientists involved in the Coupled Model Intercomparison Project (CMIP) have formed a reasonable projection for the future, called CMIP-7, which proposes that by the end of the century the increase will be around 4°C.

But the question is why. And there is no single answer. In fact, the evolution of emissions is very difficult to predict. Renewable energies are increasing and becoming cheaper, but their future is difficult to determine. Geopolitical situations are also difficult to predict: The effect of war on emissions in Iran and elsewhere is difficult to predict. The extent of coal consumption in China and India is also unknown. And, in retrospect, the efforts to forecast the abundance of oil have also been disastrous. Finally, the prediction of fluctuations in the energy transition in each country also makes the prediction very complex.

We know that between 2012 and 2013, the evolution of emissions has changed. You can see it in the graphs: they entered into a kind of plateau. We continue to emit CO₂ and atmospheric concentrations continue to rise, but not as predicted by the famous RCP8.5. The concentration of CO_2- would have been 9 ppm higher than what we are currently measuring if the evolution prior to 2012 had continued.

That’s why the Intergovernmental Panel on Climate Change (IPCC) has changed its approach. It collects scientific data and uses climate models to publish the Assessment Report every few years. The last, AR6, was published in 2023. The seventh, the AR7, is expected to leave in 2028 and should be based on the new situation. However, there are still many climate policies based on RCP8.5, such as in the ACBC, which take into account unrealistic forecasts for decision-making. Sea level rise, for example. It is difficult to know the speed at which the sea level will rise, especially if it is based on unrealistic emissions.

Gaia is not easy. When the RCP8.5 scenario was proposed, it was not a nonsense, although now the models say that we would not reach this situation even without taking measures in climate policies. It was not a nonsense, but over time it has been seen that it is not a realistic scenario. And what we now know should be reflected in the new policies that are being proposed.