Wuppertal's temperature measurements at an altitude of 87 kilometers

Atmospheric and environmental researcher Christoph Kalicinsky lives and works in a long-term experiment

In order to understand climate change, various studies and experiments are needed that are carried out internationally and interdisciplinarily. Many of these projects are primarily concerned with basic research, i.e. simply understanding atmospheric processes before any statements can be made about possible effects and recommendations for action can be developed. In one of these experiments, entitled 'Characterization of the Internal Variability of the Atmosphere` (CHIARA), Wuppertal atmospheric and environmental researcher Dr. Christoph Kalicinsky is looking at man-made and natural climate variations over time.

Phenomena in the atmosphere

"Atmospheric scientists look at phenomena in the atmosphere, try to understand them, describe them physically and, ideally, simulate them with computer models," Kalicinsky explains. The range of topics is very broad, he says. For example, some scientists deal with radiation phenomena or the clouds, while still others investigate mixing and exchange processes in the atmosphere, for example. "One difference to other physicists is also," the scientist describes, "we live in our experiment, because our experiment is the atmosphere, which is continuously changing." So, he says, there is no possibility of repeating an experiment x number of times under laboratory conditions, but of catching a phenomenon in the same form another time in the best case. Special measuring instruments are used, for example, to regularly measure the composition of the atmosphere, i.e. the trace gas concentrations, as well as the temperature over long periods of time in order to identify the development over time.

Temperature fluctuations over time

Christoph Kalicinsky works with his team in the CHIARA subproject of a collaborative project called ISOVIC (Influence of Solar, Volcanic and Internal Variability on Climate) within the large BMBF program ROMIC (Role of the Middle Atmosphere in Climate) and says: "In this project, we are investigating the influence of the sun, of volcanoes, but also of internal temperature fluctuations in the atmosphere itself, over time." He adds that this also involves possible climate effects, which they are trying to understand through long-term observations. "We then look at that in collaboration with groups from other institutes. Everyone has a view according to their expertise on particular topics. The Max Planck Institute for Solar System Research in Göttingen specializes in the sun, studying variations in solar irradiance over the past 300 years. The Max Planck Institute for Meteorology in Hamburg is studying the influence of volcanoes, and we're looking at temperature variations in the atmosphere over that period."

To do this, the Wuppertal scientists use various freely available temperature data sets from communities or institutes, as well as their own measurements at unexpected heights. "We have been observing temperatures at an altitude of about 87 kilometers from Wuppertal since the 1980s. This is a unique measurement series because of its length. We measure radiation coming from molecules in the atmosphere. At this altitude, there is a layer of excited OH molecules (hydroxyl molecule: A molecule made of one oxygen and one hydrogen atom, editor's note) and they then emit radiation from that layer. We measure this radiation every clear night." Temperatures are then determined from this data. The equipment to measure this temperature data series was also built in Wuppertal. "These devices are called GRIPS (Ground-based Infrared P-branch Spectrometer) and there are now a few of them around the world. These were further developed by a former employee of Bergische Universität and manufactured in a larger series."

Temperature measurements since 1659

Temperature measurements and weather forecasting are not disciplines of the modern age. It is true that the data series are shorter the higher one penetrates into the atmosphere due to technical developments. But ground measurements have been around for a very long time, Kalicinsky knows. "The longest known ground-level measurement is the Central England Temperature data series. That starts in 1659 for central England. But there are also measurement series in Germany that start at the end of the 18th century." That's true for Europe, he said. On other continents, the length of the data series is, of course, also related to settlement. The data series in Africa are generally shorter, he said, and in Australia, too, it can be observed very nicely that there are significantly longer measurement series on the heavily populated east coast. "There are also measurements on ship routes. You can then read that in the logbooks," he adds. Measurements at higher altitudes are difficult without tools. Balloons can be used to measure up to certain altitudes, but the essential information today is generated by remote sensing made possible by ground-, air- or satellite-based sensors, he says.

Predictions are difficult

When it comes to climate change, the whole world wants to know how to stop it and wants recommendations for action from science. However, this is difficult with regard to temperature fluctuations, Kalicinsky states, "because I am dealing with the current state and the past, but not initially with the future. It is essentially a matter of understanding the processes here. Looking into the future is difficult because we don't yet know all the causes of temperature variations." Even if measurements in the past have shown a clear temperature fluctuation, it is still impossible to say that it will always continue. Therefore, future statements regarding this point are not serious from the current point of view. When you look at long-term developments in general, it always depends on the right scales and whether you can compare data sets and if so, how. "When you compare different data series, you have to look at the time periods. If you see differences between data series, but you've looked at different time intervals, that doesn't necessarily mean that the data series also show a different picture, because temperature variations naturally have a time history and may well differ regionally."

Natural and unnatural temperature variations

Atmospheric physicists distinguish between natural and unnatural temperature fluctuations. Says Kalicinsky, "Natural temperature fluctuations are effects over which humans have no influence, which have a naturally existing drive. This can be a volcanic eruption that affects the atmosphere because it brings aerosols into the atmosphere, which in turn lead to cooling. The variation of the sun is also a natural forcing, one of the strongest forcings here in the atmosphere. All of life would not function without the sun, and temperature is also dependent on it. "The activity of the sun is subject to an 11-year cycle, which can be seen well in the number of sunspots. This has a direct effect on temperature at many altitudes. "Unnatural temperature variations are those caused by us humans. These include greenhouse gas emissions, for example, because they change the radiation balance in the atmosphere, and that again leads to temperature effects." To elucidate relationships to temperature change without using model simulations, he said, they work with several additional data series that show these natural or unnatural phenomena. These are then compared with temperature to find possible commonalities, he said. Since many things influence each other in the atmosphere, distinguishing between the different effects is not always easy, he said. "Our experiment is also in a state of continuous change," Kalicinsky says. Scientists are constantly trying to understand the complete mechanism and advance to the causes, without which a valid prediction is impossible. What is certain, however, Kalicinsky concludes, is that "there is a long-term increase in temperature, which results in a significant increase in extreme weather events. Floods, floods and droughts we notice everywhere. And what can also be detected and measured is the melting of glaciers and the retreat of ice sheets at the poles, precisely because it's gotten significantly warmer in recent years."

Therefore, findings on climate variations collected over a long period of time can also be useful in the fight against climate change in the future.

Uwe Blass

Dr. Christoph Kalicinsky conducts research at the Institute for Atmospheric and Environmental Research under the direction of Prof. Dr. Ralf Koppmann in the Faculty of Mathematics and Natural Sciences.