A recent study by the Potsdam Institute for Climate Impact Research (PIK) has shed light on the devastating economic consequences of climate change. In fact, the study was retracted due to concerns over data issues, highlighting the complexities and challenges of climate research.

From The Klima Nachrichten

By Frank Bosse

We recently reported on this unfortunate PIK study on the economic consequences of the climate.
It had to be withdrawn (after some outcry in the economic world) – unfortunately much too late. The reasons: heavily falsified data in the direction of alarms and far too little assumed uncertainties.

“Isn’t this proven mistake a nice occasion to put other forecasts and climate allocations of PIK to the test?” is a logical conclusion.

Has the certainty of “serious consequences” been exaggerated in such a way for other aspects of the climate? You then inevitably end up with the developments of the jet stream due to climate change.

This strong wind band in the upper troposphere, which blows from west to east at an altitude of 8-12 km, indeed influences the weather here very much. In our latitudes, the pressure structures on the ground follow the course of the jet stream and this is highly variable.

In January 2025, we had once again provided detailed information about some wild hypotheses about the “already visible” changes. “At some point, PIK itself must come to the conclusion that an institute should by definition take care of science and therefore not interpret a “climate impact” into every weather,” one would think.

Far from it! Last summer was quite rainy and that was the reason for an interview with the RBB radio station “Radio eins” on July 21, 2025, with PIK representative Fred Hattermann. From min 1:20 there comes quickly “the old lyre”: “The jet stream is getting weaker because the North Pole is getting warmer with less ice and that leads to extremes with us”. This time, Hattermann referred to the summer rains in Germany. Was it a coincidence that the interview appointment was also the rainiest day (9 mm of rain in the area average of Germany) of the whole summer? Hard to believe!

Was the rain in 2025 unusual overall? A look at data, showing the precipitation in mm/day:

Is there a trend (dashed) from 1980 onwards for heavy precipitation on a single day? On how many summer days did it rain more than on this July 21, 2025?

By no means a real trend! The 2.5mm/day in the area average is completely inconspicuous in the context of summers back to 1950, as is the maximum daily amount. A real trend from 1980 (onset of modern climate change) is also not discernible, between 2000 and 2010 it became a bit wetter, and the average is now, after a dip until 2021, about where it was in the 80s. So, what’s the truth in the jet stream story, since Arctic sea ice didn’t shrink until after 2000, but no longer after 2011?

To make a long story short: Nothing at all! In our January article linked above, we also showed why this is so: At the height of the jet stream, the tropics warm up more than the Arctic with climate change. This should lead to a stronger jet stream, not a weaker one, as is often claimed. The PIK representative probably sticks to the “jet weakness fairy tale” against his better knowledge (he should know the current literature on the topic he is talking about!). The years of announcing this erroneous thesis are even reflected in Google AI summaries in searches. If you type in “jet stream change”, it jumps out at you:

“The jet stream is changing due to climate change: the warming of the Arctic (Arctic amplification) reduces the temperature difference with the equator, which tends to make the jet stream weaker …”

A very recent meta-study on the jet stream (published at the end of November 2025) explains the “summer jet stream changes”:

“In summer, Arctic amplification and Rossby wave propagation are both weaker and the stratospheric polar vortex is absent, making these less important among other previously mentioned drivers. … but the agreement across models on the polewards shift suggests that tropical upper-level warming is a major driver in that season.”

There is a very slight northward shift of the jet stream and it becomes somewhat stronger due to the tropical warming caused by climate change.

That is the state of science. However, especially around the jet stream and its development with climate change, there are also huge question marks, including the question of whether the models used are even able to say anything valid about it in our country:

… which raises concerns about the ability of models to capture the North Atlantic jet response to drivers. This discrepancy could have implications for how well models capture the magnitude of the jet response to greenhouse gas forcing…

Apparently, however, the steep and unscientific claims have been hammered into a collective memory with equally unscientific certainty so successfully that “artificial intelligence” has also adopted it. A reminder to focus more on “Human Intelligence” than on “Artificial”!

The question remains why the “jet stream fairy tale” was brought into the world. The answer is obvious: This means that pretty much any weather can be attributed to climate influences.
If it rains little: “Climate impact!”, it rains a lot: “Climate impact!”
Only attention is always the goal, hardly science.

The fairy tale is, so to speak, the Swiss Army knife for all would-be climate impact explainers.

As long as they are always able to place their stories offensively in the media, the widespread superstition will somehow live on. In truth, the climate impact explainers from Potsdam are probably interested in this, not primarily in responsible science, as it should be.

But then the “I” for “institute” in the name PIK would be an oxymoron, a contradiction in terms.
But who can remember an acronym like “PKM” for “Potsdamer Klima Märchen” (Potsdam Climate Fairy Tale)?