droughts in the last decades could be related to the man-made climate change. For this assumption, scientists have found new evidence.
For the period from 1900 to 1949, the research meadows is a clear statistical relationship between droughts and the global temperature to rise. From 1950 to 1975, the air could have been clouded by the pollution of the connection, explain the researchers in the journal "Nature". For the Phase after that, the connection was again apparent.
The researchers by Kate Marvel of the Columbia University in New York (USA) took advantage of drought atlases, which are based on the evaluation of year-rings of trees: the extent of The tree growth to let inferences on the climatic conditions in the respective year. In the drought atlases, the regional soil is specified to moisture in the Form of the so-called Palmer drought Index.
allow Because the annual rings in the assessments of the climate looking back over many centuries, for the scientists a good basis for comparing droughts before the Industrial Revolution in the 19th century. Century. The data combined with simulations in computer models.
drought data from different regions of the world
The atlases are available for North and Central America, Europe, and the Mediterranean, as well as large parts of Asia and Australia. The researchers hoped that the combination of the data from the various drought atlases, a stronger statistical relationship with climate change, as he from the individual atlases read.
in fact, this is for the period 1900 to 1949 are clearly visible. Starting in 1950, but the connection in the sharp fluctuations of temperatures and droughts. The researchers suspect the cause is the influence of many particles in the air due to the increase of industrial production after the Second world war.
Andreas Fink, from the Karlsruhe Institute for technology (KIT), who was not involved in the study, explains aerosols, the attenuation of the rise in temperature, especially with sulfur. These particles would have scattered the sun's light back into space. "These sulfur aerosols, unlike CO2, short-lived and have no greenhouse effect," says Fink.
This Global Dimming effect was reversed in the mid-1970s (Global Brightening), the researchers. At the time the Filter had been installed in Europe and North America, increasingly in factories and power plants, which removed many of the pollutants, including sulphur, from exhaust gases.
Weaker connection 1980
The group in order to Marvel found a statistical connection between climate change and droughts from the year 1981. This, however, was less clear than for the period from 1900 to 1949. Reason for this could be that the time period was from 1981, commented Sonia Seneviratne of ETH Zurich, who was not involved in the study. Somewhat surprisingly, it was nevertheless, since the warming was since 1980, and higher than between 1900 and 1950.
One cannot, however, exclude the possibility that there were weaknesses in the study, for example, a contribution of regional signals associated with natural climate variability. This could amplifies the Signal from 1900 to 1950, the Signal since 1980, however, have weakened.
it should Also be noted that the information from the annual ring data for only 54 percent of the land area outside of Antarctica, as Seneviratne. Many regions such as South America, Africa, and North Asia are absent in the analysis due to a lack of tree ring data. The regions covered were rather in the mid-Latitudes, which were in the Climate projections, and a tendency to dehydration.
"The conclusions of the study are therefore likely to be robust for this area, but it is still an open question whether a global trend can be derived," said the ETH climate researcher. (ij/sda)
Created: 02.05.2019, 14:29 PM