A new study revealed that the decadal fluctuations in the water temperatures in the Pacific are directly related to the temperature of the middle atmosphere.
The new study, published in the journal Scientific Reports, suggests that natural variability remains a dominant factor affecting the tropopause, despite increasing evidence that human activities also play a role in the temperature change.
Tropopause is the layer between the atmosphere between the troposphere and the stratosphere.
For the study, the researchers analyzed observations from 1979 to 2013 and climate models. With these, the researchers were able to extend their study period for nearly 150 years, making it easy to look at both human and natural influences and separate their impacts from one another.
The researchers discovered that the natural variation caused by the Pacific Decadal Oscillation (PDO) is not only influencing the climate and ecosystems in the Pacific Region, but also affects the global mean temperature of the Earth. PDO is a climactic phenomenon that leads to the anomalously high and low temperatures in the pacific.
According to a press release, new model simulations developed by the researchers showed that the fluctuations in the water temperatures caused by the PDO affects the wind systems over the tropical and subtropical. Changes in the wind systems lead to the altering of the air transport between the lower and upper layers of the troposphere, leading to the regulation of the temperature at the boundary of the stratosphere.
These new findings contradict to earlier hypothesis suggesting that Earth has been experiencing a cooling trend since 1970s due to the increased levels of greenhouse gases.
Our study shows that the cooling of the tropical tropopause does not have to be a one-way street but could also be part of a natural fluctuation which extends over several decades," explained Prof. Dr. Katja Matthes, climate researcher at GEOMAR and co-author of the study, in a statement.
Researchers noted that the temperature in the tropopause is reliant in the input of water into the stratosphere. The higher the water vapor content in the stratosphere, the higher the increase in surface temperatures. Although human activities also affect the temperature of the tropopause, researchers will be able to make more reliable forecast of the development of the climate if they can clearly distinguish the influence of natural variability.
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