Downgrades: Global warming

The announced global warming could well take place. This issue seemed to be unanimous among hundreds of experts from around the world gathered at the United Nations Intergovernmental Committee on Climate Change (IPCC) on February 19, 2001.

The temperature of the air has increased on average by 0.6 ° Celsius during the twentieth century. This may seem very small, yet only 7 ° Celsius separated the ice age of our planet 20,000 years ago, from the warmer one it experienced 7000 years ago! The first consequences of this warming are already visible: a 10% decrease in snow cover in the Northern Hemisphere since the 1960s, a decline of mountain workers, a rise of 10 to 20 centimeters in the level of the oceans during the 20th century , increased precipitation, floods or droughts, thawing of permafrost ...

Today, almost all scientists agree to attribute most of this evolution in the last decades of the twentieth century to greenhouse gases produced by human activities. The main culprit is carbon dioxide, which accounts for 70% of emissions, followed by methane . Their concentration in the atmosphere has not stopped increasing since the beginning of the industrial era: since 1750, the concentration of carbon dioxide has increased by 31% and that of methane by 150%. Some of these gases remain in the atmosphere and the rest are absorbed by oceans and plants.

If today, the state of the scientific knowledge and the models used by the climatologists do not make it possible to make fine predictions on the regional scale, they make it possible to globally predict the big evolutions which it is necessary to expect. However, the forecasts are alarmist: a warming of 1.4 to 5.8 ° Celsius is indeed expected by the end of the 21st century, the greatest increase that the Earth has known since about 10,000 years.

But make no mistake. Our planet will be warmer but it will also become more humid. The models predict that the new distribution of rainfall would further accentuate the existing inequalities: the equatorial regions would receive more water, in contrast to the subtropical and Mediterranean regions whose drought would increase and whose water resources would decrease. Finally, the most fragile countries with regard to their water resources would become even more so.

In addition, by 2100, scientists predict partial or total melting of glaciers, 98% of which are currently in decline, and an average rise in sea level of between 9 and 88 centimeters.
If nothing is done, some changes may become irreversible beyond the second half of the 21st century. The only way to slow down this development is to reduce greenhouse gas emissions.

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