Surprising insights into climate change

The tropopause, the shifting layer between the troposphere and stratosphere, has increased by about 200 meters over the past two decades, primarily due to greenhouse gases and ozone

Climate researchers from the USA, Germany and Great Britain present model calculations in Science that shed new light on the climatic changes caused by the earth’s inhabitants. Whereas previously the focus was on the temperature rise on Earth or in the stratosphere, scientists are now looking at the tropopause as a marker for unpredictable climatic changes. The calculation is based on satellite data for the period from 1979 to 1999. Using information on greenhouse gases, aerosols, ozone, solar energy and volcanic activity, scientists simulate the conditions for the 20th century. Century. According to their time series analyses, the temperature has been changing rapidly over the last 20 to 30 years: in the troposphere it is rising by about 0.07 degrees Celsius per decade, while in the stratosphere there is a cooling of the same order of magnitude.

Surprising insights into climate change

Time series analysis of tropopause thickness obtained by simulation. Sum and single effects

Simulations

Tropo-, strato-, meso- and thermosphere are outline elements characterized by physical and chemical properties. The hand rule, according to which the troposphere reaches up to a height of 10 km, and the stratosphere from 11 to 50 km, can be well justified by prere, temperature and humidity. The tug comes with increasing detail because, for example, temperature and prere behave differently, and wind and eddy motions are themselves vectors in their own right. Earthly weather runs in the troposphere with a penetration that can be measured in days. The transition into the stratosphere, however, takes 4 weeks and more. The rise in temperature in the troposphere and the cooling in the stratosphere therefore raises the question of how the opposing processes can develop.

The earth’s atmosphere is almost transparent for solar energy. Therefore, the temperature on the surface of the Earth is usually the highest, while the UV-absorbing ozone has its temperature maximum at 0 degrees Celsius. From this point of view, the intermediate zone at the transition from the troposphere to the stratosphere has a special role: mediating, challenging or blocking. However, simulation models are designed to estimate the interactions at the state coarseness, in this case the spheres, because, as Hartmut Bossel described it, "the system behavior is to be seen as a mixture of inherent dynamics and reaction to the environment. The exact behavioral response results from the elements of the system and their structural interconnections." In this sense the displacement layer is a virtual coarse. Climatologists do not leave any doubt about it either "We have shown that stratospheric cooling and tropospheric warming increase the height of the tropopause. However, the relative influence of both factors remains uncertain", explains the scientific director B.D.Santer. Furthermore, the presented simulations are an attempt to explain satellite measurement data retroactively and to infer the future from it. B.D.Santer refers to the earlier publication of the working group from May 2003 in Science. As a preliminary work to the present analysis, they determined, according to the rules of time series analysis, a "fingerprint", a kind of fingerprint, because the calculation of the temperature leads to different results depending on the choice of satellite data.

The interactions due to the measurement samples (greenhouse gas, aerosol, ozone, solar energy and volcanic eruptions) are modeled as average values and in comparison to pre-industrial data, without separating human-induced and natural sources. For the extent of the tropopause, scientists reduce their considerations to a single layer, which they define by the World Meteorological Organization (WMO) temperature gradient.

Tropopause: the unknown zone

Although the Earth’s atmosphere is thought of in layers, the troposphere, which reaches up to 11 km in height, accounts for about 80 percent of the mass. In the troposphere the temperature drops with 6.5 degrees Celsius per km to about -50 degrees, to rise to 0 degrees in the stratosphere (up to 50 km). The tropopause, discovered in the 1980s, is defined by the adiabatic temperature gradient and has different highs: near the aquator (25.latitude) 18.3 km (100mb), in the middle range (35.-40.Latitude) 12.2 km (200 mb), and polar 9.1 km (300mb). However, the conditions are not stable. Tidal changes in the air layers as well as seasonal effects contribute to this.

Also, the temperature gradient is not always positive and stabilized in the sense that the warm air lies above the colder and denser air masses. Locally and rather quickly, an inversion with a negative temperature gradient can occur: through an increase in the earth’s surface temperature or cooling at a coarse level. Meteorologists and pilots are learning to deal with these circumstances, and know that despite the forecasts, much that is unpredictable remains in play. In this respect, the tropopause is not a stable or stably conceivable layer. If one goes into detail, multiple overlaps become recognizable, as well as regionally different temperatures. For example, the tropopause is considered by meteorologists to be a particularly dynamic layer because of the sometimes violent eddy movements.

And finally, the WMO even defines the condition of a second tropopause: the 1.Tropopause is characterized by the lowest altitude (beyond 500 mb), from which the temperature gradient drops by 2 degrees Celsius per kilometer or less. However, if a drop of 3 or more degrees Celsius is observed at an even coarser level (up to 2 km after the first tropopause), a 2.Tropopause formed.

Surprising insights into climate change

Profile of the tropopause for a flight from Alaska to Hawaii. (Explanation in the text, more pictures on the website of MTP)

An impressive example of the inhomogeneity of the tropopause has been published on the Internet by NASA. The graph shows the temperature conditions for a flight from Alaska (right) to Hawaii (left). There exists between the 38.-42. latitude the 2.Tropopause. Furthermore, the interruption at the 54.latitude can be seen that air from the stratosphere gets under the tropopause and lifts the tropopause. The profile also shows that the flight takes place partly in the troposphere and partly in the stratosphere.

Unwieldiness

In the discussions about global warming, everyone agrees that opinions clash emotionally. This is due to personal views and political demands that, consciously or unconsciously, influence the scientific research and arguments. Furthermore, the increasing preoccupation with global warming shows that there are still far more imponderables than proven facts. On the way from the active and polluter pays principle to the Kyoto solution, research stumbles at the demand to distinguish human abuse, human necessities and natural sources from each other and to make the proportions measurable in absolute numbers.

The results of B.D. Santer and collaborators expand the horizon of observation to include a new debate about principles. The supporters of the Kyoto Protocol will see their fears confirmed. Opponents and critical voices striving for objectivity will find fault with simplification. One meteorologist, asked about the new insights, grumbled: "If it was so simple up there blob! Then we had no more problems with our predictions."

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