Updated: Sep 25, 2020
This article is the first in a series focusing on explaining the causes and effects of climate change.
Although the Earth's natural climate over the past million years has oscillated between warm periods and ice ages, today's global warming is attributable to human activity.
The climate changes linked to a natural cycle are different from the global warming caused/influenced by man. For a long time, opponents of the human-induced warming thesis hid behind the idea that this warming could simply be another natural cycle.
Many of today's human activities generate so-called greenhouse gases (such as carbon dioxide, methane, nitrous oxide, fluorinated gases). Increasing the concentration of these gases in the atmosphere generates an effect similar to the glass of a greenhouse (hence their name), by trapping the sun's heat and preventing it from escaping into space.
The first scientific evidence of the risk of an increase in the greenhouse effect through human activity traces back to 1896, when the Swedish chemist Svante Arrhenius concluded that the combustion of coal in the industrial era would enhance the natural greenhouse effect. This was followed by confirmation in 1900 by Knut Angstrom, who discovered that carbon dioxide (CO2) strongly absorbs parts of the infrared spectrum, even in tiny concentrations in the atmosphere. This confirmation demonstrates that even a trace of this gas can produce a warming greenhouse effect.
In 1938, a British engineer, Guy Callendar, used data from 147 weather stations around the world to show that temperatures had risen over the previous century. Similarly, he showed that CO2 concentrations have increased over the same period, and suggests that this has caused a global warming. But at this point, this effect, called Callendar, however, is widely dismissed by meteorologists.
It was not until 1962 that unequivocal proof of rising CO2 concentrations was obtained, thanks to an equipment developed by Charles David Keeling, which allowed systematic measurements of atmospheric CO2 for four years (and continuing today) at Mauna Loa in Hawaii and Antarctica. Yet these results are not enough to raise awareness of the risks.
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