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[EN VIDÉO] The North Pole seen by Florian Ledoux Florian gives himself up to Futura after two months of expedition on the Svalbard archipelago. He tells us how he perceives nature and why it is so important.
Different geological objects record temperatures continuously over time and play the role of memory of the Earth. The analysis of these archives makes it possible to obtain accurate temperature values from the past and thus to reconstruct the history of the Earth’s climate over a considerable period.
By reconstructing the Earth’s climate, we see that it oscillates between two major climatic states which depend on the presence or not of ice at the poles: there is a first dominated by globally cold temperatures and characterized by the presence of ice at the poles, called the ice age; and a second dominated by globally warm temperatures and characterized by the absence of ice at the poles, called the interglacial period.
The swing between a glacial period and an interglacial is very long and takes place on a 100,000 year cycle. It never shows a stable, linear transition; abrupt, even dramatic changes are observed in past temperatures.
Dansgaard-Oeschger event
During the last ice age, for example, these rapid temperature changes were called ” Dansgaard-Oeschger events ” (Where DO events); these are shifts that will induce warmer periods — during the last cold period –, then will gradually return to a stable cold phase. The climate system therefore adopts a state of bi-stability, that is to say two stable climate states that can switch from one to the other.
These DO events occurred 25 times during the last ice age and had significant repercussions in the Arctic where temperatures reached up to 16 degrees Celsius in a few decades. These events are rather mysterious and leave many questions unanswered. Scientists do not know what causes it or their durationtheir strength, or why they appear to be regular.
The “window of instability” of CO2
Guido Vettoretti and his colleagues at the Institute Niels Bohr (NBI), from the University of Copenhagen in Denmark, looked into it and concluded that CO2 had a major influence. In their study published in Nature Geosciencethey work with two climate models that end up showing the same global behavior, which is in agreement with the acquired geological data.
They find that the instabilities of the climate system (the DO events) have occurred when the amounts of CO2 in the atmosphere were between about 190 and 225 parts per million (ppm); they therefore demonstrate that the occurrence of these abrupt climatic events was controlled by CO2 as follows: the climate system becomes unstable when the rate of CO2 is between about 190 and 225 ppm.
Above 225 ppm, the climate of the North Atlantic shows a warm and stable state; below 190 ppm, it is in a cold and stable state. But, between these two levels, the climate system enters a “ window of instability” where it switches between warm and cold periods.
According to Vettoretti, this study is important because it shows that under different levels of CO2 in the atmosphere, temperatures can react quickly and unpredictably. It is necessary to understand whether the current increase in CO2 will cause sudden changes in the climate and even tip it into a new irreversible state.
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