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Throughout geological history, the planet has been dominated by a warm climate. Only twice in the past half a billion years have there been long-term cooling periods, including the current one, which lasts about 34 million years. Ice ages were accompanied by a decrease in the concentration of carbon dioxide in the atmosphere, but the reasons for this are not clear. In a new study, scientists have built a model that combines all the hypotheses of climate cooling. This allowed us to explain the polar glaciation that we are observing now.
According to modern ideas, the concentration of CO2 in the atmosphere affects the temperature on Earth. Tectonic mechanisms are used to explain the geochemical cycle of carbon on a scale of tens to hundreds of millions of years. It is believed that as a result of degassing from the lithosphere CO
2 enters the atmosphere, and the weathering of silicate minerals of the Earth's crust, especially on continents and in ophiolite zones, on the contrary, removes it from there, binding it in carbonate minerals. During weathering, mineral components necessary for biomass nutrition are also released, which, in turn, triggers the mechanism of absorbing carbon dioxide from the atmosphere and burying them in the form of organic matter.
Over geological time, tectonics and weathering have significantly changed the appearance of the planet. Particularly large changes occurred in the Phanerozoic (the last 538 million years), which is mainly associated with the colonization of the surface by life. Models have been developed that reconstruct the climate on Earth based on different mechanisms, but their results are contradictory. They have not answered the question of which mechanism is leading in this matter.
Scientists from Australia, France, and the UK decided to investigate the problem. To do this, they used a continuous model of the Earth system (Earth System Model), starting in the Devonian period, 419 million years ago. Earlier periods had to be excluded due to a lack of reliable data. The authors also did not assess how the spread of vegetation affected glaciation. The results of their work are published in the journal Science Advances.
The model showed that the current cold state is not typical for the Earth, which has been in a warm climate for most of its history. The glaciation of the poles was caused by a coincidence of several factors. To explain the ice ages, geologists have put forward various reasons: volcanic eruptions, the increasing role of forests that store carbon dioxide, chemical reactions of CO2 with geological rocks. All of these mechanisms were tested in the SCION 3D Earth model, originally developed at the University of Leeds (UK). Calculations showed that none of the mechanisms alone could have led to climate cooling; a simultaneous combination of factors was required.
"We found that the reason we live on a planet with polar caps rather than an ice-free one is a chance combination of very rare outbreaks of global volcanism and a large spread of continents with high mountains, which provide heavy rainfall on the planet. This, in turn, enhances the reactions of carbon absorption from the atmosphere," explained the study's leader, Andrew Meredith from Leeds.
An important conclusion, according to the scientist, is that the natural climate regulation mechanism leads to high concentrations of CO2 and warming without ice caps, not because of what we see now.
"We believe that this general trend toward warming protects us from the disastrous 'Snowball Earth' state, which occurs extremely rarely and is the only reason life continues to exist," Meredith added.
Based on this, it should be taken into account that the planet's climate will not tend to the cool state it was in in the pre-industrial era. We need to be careful with claims that the cold climate will return if we overheat it before we stop emissions, the authors warned.
