Science
About 55 million years ago, extreme heat waves engulfed our planet. The Earth's surface has warmed to an average of 5 degrees Celsius. Then, after a relatively short period of time, the heat subsided, although two more slightly less hot periods followed.
Based on the chemical composition of the rocks, scientists have suggested that high levels of carbon dioxide influenced global warming at the time. But where does so much of this greenhouse gas come from?
The team of researchers suggests that this carbon dioxide came from the fact that permafrost (frozen soil containing organic material) began to melt after passing through Earth certain cycles of revolution around the Sun that allowed the poles to warm up. Due to the melting, a huge amount of carbon dioxide was released into the atmosphere, which did not allow sunlight to reflect, so the planet began to warm up very much.
Previously, scientists theorized that the atmosphere was changed by methane, which was released from marine sediments. However, recent research, published in early April in the journal Nature, showed that methane was not enough for such a serious warming.
According to other theories, it could be a comet, violent fires, or the drainage of shallow inland seas. However, these theories can't explain the less intense periods of warm climates that followed later, say Mark Pagani, a professor at Yale University, and colleagues.
After examining rock outcrops near Gubbio, Italy, which contain evidence of periods of heat waves in the past, scientists found that these periods coincided with cycles Earth's orbits around the Sun.
The path that the Earth takes around the Sun and the locations of the other planets may differ slightly according to cycles that last a maximum of 100,000 years. Scientists have found that the three major periods of warming, which began 55 million years ago, coincide with the periods when the Earth's axis was most tilted and when the planet's orbit was the most eccentric, that is, the least round.
This meant that higher latitudes, areas near the poles, experienced longer and warmer summers, so the permafrost began to melt there. As a result, the melting of the permafrost released more carbon dioxide, became warmer, and so on.
Scientists are focusing on discussing the melting of permafrost in the northern hemisphere. But for 50 million years, the planet was warmer than it is today, so Antarctica wasn't covered in ice like it is today. Scientists suggest that the southern continent probably had its own carbon stored in permafrost.
After warming reached its limit in 10,000 years, permafrost carbon stocks should have been depleted. As a result, carbon dioxide accumulated in the atmosphere, which remained there for about 200,000 years until natural processes removed it. The planet has gradually cooled down.
Then, after about 1 million years, the process began to be repeated, but on a smaller scale, as by then there was less permafrost that could melt. Less intense warming has been observed.
Compared to that period of global warming, our planet is warming much faster today. Scientists believe that the melting of Arctic permafrost may further exacerbate the situation.
“Permafrost is an important source of carbon that has not yet been released, but its release is just around the corner,” Pagani said.