Satellites are to measure storms in the greenhouse

Satellites are to measure storms in the greenhouse

On Sunday, the guests also discussed wind on Sunday. Will climate change give us more storms besides melting glaciers – or even more violent ones? That’s harder to answer than it seems.

On the talk show “Anne Will” Sunday’s “Fridays for Future” demonstrations were staged by 16-year-old Swede Greta Thunberg. The guests debated above all on the question of whether participating in the demos could justify the truancy of protesting children and adolescents.

On the sidelines, it was in the round, consisting of the Dortmund “Fridays for Future” activist Therese Kah, the Deputy FDP Chairman Wolfgang Kubicki, the Green Party Chairman Robert Habeck, the Prime Minister of Saxony-Anhalt Reiner Haseloff and the scientist Harald Lesch, even something else: the topic of wind.

If devastating storms, such as in the US once arrived in Europe, would be talked about compulsory education, said Lesch in this context. That’s for sure. But it raises the question of whether there will be more or even more severe storms in Germany due to climate change. What risks threaten us by weather extremes?

The world sleepwalks into disaster

At the beginning of the annual World Economic Summit in Davos, an expert report with the greatest risks threatening humanity will be presented at the end of January. For the first time in the history of the World Economic Forum (WEF), three of the top places in the history of this year all identified challenges arising from global climate change.

The biggest concrete risk identified in this report was the increase in weather extremes. The authors of the WEF study find drastic words: “Of all the risks, the most obvious to the environment is that the world is sleepwalking into disaster.”

According to analyzes by the world’s largest reinsurer, Munich Re, tropical cyclones last year caused economic losses of more than € 44 billion – well above the long-term average of around € 30 billion. However, in 2017 there was a special catastrophic year in which hurricanes even caused damages in the hundreds of billions of dollars.

Fortunately, there can not be tropical cyclones in Germany because they draw their energy from the warm surface of the oceans. They always grow over the oceans to turbulent monsters before they may hit a coast and then cause great devastation on land. But even “normal” storms, which result simply from the atmospheric gradient between high and low pressure areas, can certainly cause devastating damage.

The fact that heavy storm events have occurred in Germany over the past few years has not only been noticed by customers of Deutsche Bahn in view of day-long road closures as a result of the trees falling on the tracks. The Gesamtverband der Deutschen Insurer (GDV) reported a loss amount of EUR 2.6 billion for storms in 2017, compared with EUR 1.6 billion in the previous year. And even in 2018, says GDV CEO Wolfgang Weiler, was one of the four heaviest storm years of the past 20 years.

Is the increase in the strength of storms a consequence of global climate change? And do we have to expect more violent storm events in the future? A proof that a concrete storm is the result of climate change can not be provided in principle. After all, there have always been storms – even very violent ones – and not just since the industrial age. So, this is about the question of whether the number and / or the intensity of heavy storm events has already increased or will continue to increase in the future.

The data are not yet sufficient to statistically provide clear evidence that climate change is responsible for an increase in strong winds. So far, there is not even a global measurement of the winds, so that one could conclude that there is an average wind energy and, if necessary, an increase in this value.

The scientific evidential force looks different at the mean global temperature of the earth’s atmosphere. Recently, US researchers at the National Oceanic and Atmospheric Administration (NOAA) have pointed out that since the beginning of the Industrial Age, the mean temperature on our planet has risen by one degree Celsius. This can hardly be doubted and can also be described well with the existing climate models.

A look into the past is always easier than looking into the future. The variability of the relevant parameters and the uncertainty of the mathematical models is so great that it is forecast by the IPCC researchers, the Intergovernmental Panel on Climate Change, that a temperature increase of two to five degrees Celsius will be reached by the end of the century. But it is clearly a rise. The weather service reported that 2018 had been the warmest year since weather records began.

Higher temperature means more energy

Although in the storms such a clear forecast as in the temperatures is not yet possible, so you can still make some basic predictions on the subject of wind. Physicists can sometimes make startling predictions without having the knowledge they need to know: as the Earth’s mean temperature increases, so does the energy in the atmosphere.

But if more energy exists there, then this energy can also be converted into weather events. It is plausible that in a warmer world there will be more thunderstorms, more storms and more hail – and more turbulence that will shake up passengers.

So far the theory. However, from this fundamental consideration, it is not yet possible to deduce in detail where specific weather capers are to be expected. The weather remains a chaotic, highly statistical matter that only reveals the climatic trends with a view over years and decades. Although there is much research work to be done at this point, the German Weather Service expects an increase in storms on the basis of observations to date in this country.

In the tropical cyclones, the scientific context seems to be easier at first glance. If, as measurements show, the surface temperature of the oceans increases, then in principle more energy is available for the evaporation of water. Hurricanes can then become stronger and more dangerous. But whether this will actually lead to a greater number of tropical cyclones is still the subject of scientific analysis and discussion.

In order to better understand how the energies are distributed in the highly complex global wind system and where ultimately more and possibly less wind can be expected, one would first have to have a situational picture of where exactly which wind blows with which magnitude – and that worldwide and across the various atmospheric layers.

Not only would that allow for better weather forecasts, it would also make it easier for climatologists to better understand the dynamics of the Earth’s atmosphere. Better climate models, in particular better statements about the probable increase of strong wind events would then be conceivable.

Surprisingly, there is only one satellite available so far that can measure such global wind profiles and wind speeds at different altitudes. It is the Esa satellite “Aeolus”, named after the Greek god of the winds, which was shot in August 2018 in a roughly 300-kilometer high earth orbit.

The 1.4-tonne satellite orbits the earth 15 times a day. “Aeolus” scans the atmosphere with the light pulses of a UV laser. The light backscattered by the molecules can then be picked up by the satellite. It hides the information about how fast the molecules are moving.

Surveying the earthly winds remains a future goal
But “Aeolus” is initially only a satellite with which the new measurement technology is to be tested. If one really wanted to measure the winds worldwide in the earth’s atmosphere, one would need at least six such satellites. So we have many years of global wind mapping in real time.

For the time being, it will remain so, that after each storm disaster the question will be asked again: “Was climate change responsible for that?” And the answer will be something like this: In individual cases, that can not be said. But there is much scientific support for the fact that there must be more storms.