Humanity is concerned about climate warming in the coming decades. But few people think that in thousands of years he should expect the onset of a new ice age. However, the discovery of a biological mechanism slowing down the global cooling gives rise to hope that the Earth is not threatened with complete glaciation.
Scientists believe they have learned something important about the ice ages. In conditions when the content of carbon dioxide in the atmosphere drops to a new minimum and glaciers begin to move from the poles to temperate latitudes, a mechanism must be triggered that will stop this process.
There is evidence that in the distant past, our planet already experienced a complete glaciation, when the glaciers reached equatorial latitudes. The hypothesis of "Snowball Earth", expressed half a century ago, is based on them. It is assumed that the last such era occurred more than 700 million years ago, even before the ocean and land were inhabited by complex biological organisms.
This is where researchers approach fundamental questions in geophysics. We know that long before the appearance of man, ice ages were replaced by periods of warming. Glaciers were advancing and receding, the concentration of carbon dioxide in the atmosphere fell and increased. What caused these changes remains largely a mystery.
Astronomical and geological factors are most often named among the factors responsible for the alternation of cold and warm periods in the history of the Earth. The former include the precession and nutation of the earth's axis and fluctuations in the eccentricity of the earth's orbit. Geological causes are volcanic activity, mountain building and continental movement. Recent studies give reason to consider biological factors along with this.
It is the biological causes of climate change that were discovered by two Spanish scientists from the Autonomous University of Barcelona and described in an article in the journal Nature Geoscience. Experts measured the content of carbon dioxide in ice cores and determined its lowest level.
“We have found that over the past 800,000 years, atmospheric carbon dioxide has hovered around 190 ppm most of the time and never dropped below,” said Sara Eggleston of the University of Barcelona's Institute of Environment and Conservation Technology. “This unexpected result indicates that such a very low concentration of carbon dioxide was quite stable. Moreover, we know that in the distant geological past, the CO2 content has often increased, but we have no evidence that it has ever dropped below 190 ppm.”
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Scientists from Barcelona are cautiously suggesting that the biosphere may have played a role in containing the sharp drop in temperature on Earth. At very low CO2 levels, photosynthesis in plants and plankton was hampered, which slowed their growth. As a result, the amount of carbon dioxide on land and in the ocean should have decreased, and in the atmosphere - increased, increasing the greenhouse effect. If this is true, then life itself acts as a regulator, preventing the planet from cooling too much.
The result obtained speaks in favor of the Gaia hypothesis, put forward almost forty years ago by the Briton James Lovelock. The scientist argued that living organisms, acting collectively, but unconsciously, ensure the maintenance of stable environmental conditions through various feedback mechanisms.
Thus, in the regulation of the climate, the biological factor is more important than the geological one. “It is known that over hundreds of thousands of years, the CO2 content in the atmosphere changes due to the slow interaction with rocks,” explains study leader Professor Eric Galbright. “But this is too slow a process to be responsible for stable periods of only a few thousand years. Therefore, when CO2 levels are very low, some other mechanism must be activated.”
Now that climatologists have established the existence of a lower limit for the level of carbon dioxide in the atmosphere, a catastrophic glaciation of the Earth seems unlikely.
Alexander Surkov