In a paper published in Science, researchers from Oregon State University and other institutions concluded that small fluctuations in the rotation of the Earth are primordial to the ice age reaching the highest level of about 26,000. last year, stable for 7,000 years and began to melt around 19,000 years ago, putting an end to the last ice age.
The first melting process is due to an increase in solar radiation intensity, not a change in the level of carbon dioxide or sea temperature as some scientists have identified in recent years.
Peter Clark, professor of geoscience at OSU, said: 'Solar radiation is the trigger for the melting process. There are also changes in atmospheric carbon dioxide levels and ocean currents, but these factors occur later and extend a process that has already begun '.
These findings are important, scientists say, because they give researchers more accurate understanding of the melting process of ice sheets before radiation mechanisms. And even though the changes that occurred 19,000 years ago were due to the increased solar radiation intensity, that heat could have the same effect as the current level of greenhouse gases, and help scientists predict a way. more precisely the future reaction of the Earth's current ice sheets.
Clark said: 'We are now sure of the reaction of ancient ice sheets to solar radiation, and this will be very helpful in understanding what might happen in the future.'
To carry out their analysis, the researchers used 6,000 data positions and dates of ice sheets to determine, with a high degree of accuracy, when they began to melt. Through this analysis, they confirmed a theory developed over 50 million years ago that small changes in the Earth's rotation were the cause of the ice age.
Clark said: 'We can calculate changes in the Earth's rotation and shaft 50 million years ago. These changes are mainly due to gravity from larger planets, such as Jupiter and Saturn. These planets pull and push the Earth very slightly in different directions for thousands of years. '
This changes the Earth's axis - its tilt to the sun - about 2 degrees for a long time, and leads to changes in the sun's rays reaching the Earth. And small changes in solar radiation are the cause of successive ice ages of about 2.5 million years ago on Earth, reaching a maximum in the 100,000-year cycle.
Scientists say the Earth will change from a time of glacial ice over the last 10,000 years and change back to conditions that will lead to an ice age - some of which have stopped. or slow down the process.
Clark said: 'One of the biggest concerns today is the response of Greenland and Antarctic ice sheets to global warming and the rise in sea level. This research will help us better understand that process, and improve the accuracy of scientific models. '
The study was conducted in collaboration with scientists from the Canadian Geological Survey Program, University of Wisconsin, Stockholm University, Harvard University, US Geological Survey Program, and University of Ulster. The research is funded by the National Science Foundation and other institutions.