COMMENT - Climate forecasts are increasingly dispensing with extreme scenarios. This makes the assessment of climate policy more realistic – finally

Global warming is progressing - according to climate researchers, January was the warmest since measurements began. Solutions are urgently needed. People want to know how much a determined global climate policy would achieve. And for comparison, we also want to know what would happen if we do too little for the climate.

These questions are difficult to answer. Ideally, one would try to back up the answers with plausible figures, but in the past this has happened too rarely. Instead, one has often relied on speculative extreme scenarios that invite emotionalized worst-case descriptions. This has placed a burden on climate policy in the public eye that it does not actually have to bear.

But now something is finally changing – the extreme scenarios are gradually being phased out. It's about time.

In order to estimate how effective decisive climate policy would be, scientists make predictions of temperature, precipitation and other climatological variables. They start these predictions under different conditions: in one case, humanity emits a lot of greenhouse gases, in another a medium amount, in another very little.

Depending on the level of greenhouse gas emissions, climate change will vary in severity by the year 2100. For example, the UN Climate Council's reports state: With determined climate policy, global warming will remain below 1.5 degrees. With mediocre climate protection, it will be almost 3 degrees warmer. With particularly high emissions, without significant climate protection, the temperature could rise by 5 degrees. This would lead to an extreme rise in sea levels and other serious consequences.

The only problem is that some of the predictions are extreme, and that is due to the data they are based on. The predictions depend on scenarios that describe how much greenhouse gas will be emitted in the future. This emission is determined by many factors: population growth, energy sources and economic growth. Some of the scenarios make extremely unrealistic assumptions about these factors.

According to the highest scenario, more than 100 billion tons of _CO2 would be emitted per year after 2060 - that would be more than twice as much as today. If you make predictions using this extreme scenario, you get the 5 degree warming mentioned at the beginning.

But the worst-case scenario is based on conditions that are no longer considered realistic today. Many scientists say they never were.

One of these conditions is that coal consumption will increase significantly by 2100 - it would have to at least double, perhaps even increase much more. This was always very speculative and is no longer a plausible assumption today. According to the International Energy Agency , global coal consumption will stagnate in the coming years . Many countries want to move away from coal.

At the same time, the growth of renewable energy sources should be very weak, which completely contradicts the latest figures. In fact, the expansion in recent years has far exceeded forecasts. Solar energy, for example , is currently experiencing a boom that is unparalleled .

Furthermore, the highest emissions scenario assumes far too high economic growth. However, growth has slowed in recent years. The population growth assumed for the scenario is also unrealistic. Several institutions have revised their forecasts downwards, such as the United Nations Department of Economic and Social Affairs .

Despite its implausible assumptions, the scenario with the highest emissions was by far the one most frequently used in studies on the effects of climate change just a few years ago. It was often wrongly referred to as a "business as usual scenario". But this label is not accurate: even if we continued to do business as before, future emissions would be much lower.

The use of the maximum scenario in science is now declining. But many media outlets are still eagerly jumping on studies that have found severe consequences of climate change based on this scenario. They find plenty of fodder in them for emotionalized horror stories.

However, it would be inappropriate to criticize all studies that used the maximum scenario. From a purely scientific point of view, it can make sense to assume high emissions, because then the climatic reaction is particularly clear. But the name of the scenario and the communication in media releases must be correct. And the media should correctly classify the results of studies based on it.

This problem is not purely semantic; it also has political and economic implications.

The influence of the emissions scenarios can hardly be overestimated, wrote Matthew Burgess and Ashley Dancer in the journal Nature Climate Change at the beginning of the year . These scenarios were not only used to predict the climate, but also to discuss how much rich countries would have to pay poorer countries for climate damage. Information that helped banks and insurance companies make decisions about climate protection and adaptation to climate change was also based on them.

In the past, a comparison was often made to illustrate the effectiveness of decisive climate policy. The most extreme scenario played an important role: the scenario with the highest greenhouse gas emissions was usually compared with a scenario with the lowest emissions. The difference in warming (5 degrees versus 1.5 degrees) was then very large - so large that the impression was created that climate policy was actually able to make the difference between hell and paradise.

This is by no means to deny that climate policy makes sense, provided the benefits and costs of the measures are carefully weighed up and other political goals are included in the assessment - for example, the goal of providing poor countries with access to inexpensive energy sources. However, exaggerations are not appropriate to emphasize the benefits of climate policy measures. The effectiveness should be demonstrated using plausible figures, otherwise the wrong decisions will be made based on the information. In addition, credibility suffers.

Fortunately, calls from the scientific community to take a closer look at the use and communication of scenarios are becoming louder and louder. Burgess and Dancer , for example, have proposed calling the most extreme scenario an "emissions world avoided" - a fictitious future with extremely high greenhouse gas emissions that could have been avoided.

A realistic look at climate policy shows that warming of 1.5 degrees is practically unavoidable. It will be a huge challenge not to exceed the 2 degree mark. If humanity only tries to reduce emissions with moderate ambition - that is, if it acts in a similar way to what it has done in recent decades - we may end up with a warming of 3 degrees. That is problematic enough, especially for Africa and South Asia, which are particularly vulnerable to climate change. But it is a long way from a 5 degree warmer world.

1.5 degrees versus 3 degrees: This comparison paints a much more plausible picture of what climate protection can protect us from. It is a good sign that experts are calling for more realism in the scenarios. This step was long overdue; theoretically it could have been taken years ago. But better late than never.