In a new study, the authors examined calcite and similar rocks on the walls of several caves in the northern United States and Canada: the age of stalactites, stalagmites and other calcite deposits in these caves is about 1.5 million years.
Next, the researchers measured the proportion of uranium and thorium isotopes in these deposits and found that about 400 thousand years ago, there was no permafrost in almost the entire territory of present-day Canada and Alaska beyond the Arctic Circle. Similar warming has occurred in the past.
On the one hand, our observations and similar measurements in Siberia show that the climate of the entire Arctic became more stable about 400 thousand years ago. On the other hand, we did not find evidence that in earlier eras, due to the melting of permafrost, there were sharp surges in the concentration of greenhouse gases.
It is noted that in the same period the climate in Siberia changed in a similar way. This means that permafrost was unstable for most of the Pleistocene. However, it’s melting, for still unknown reasons, did not in any way affect the Earth’s climate and the concentration of greenhouse gases in its atmosphere.
One of the reasons for such drastic changes, the authors say, could be the periodic disappearance of permafrost, which prevented the organic matter from accumulating in large quantities.
However, climatologists do not exclude that methane and carbon dioxide, which were formed in the process of decomposition of the remains of plants and animals, could be absorbed by someone or something.