The beginnings of understanding climate change date back to September 1933. That year, American meteorologist Joseph Kincer asked a disarmingly simple question: “ Is the climate changing ? » This question would mark the beginning of a long scientific quest to decipher the extent of human influence on the earth’s climate.
Five years later, British engineer Guy Callendar provided the first element of an answer, demonstrating a rise in Earth’s temperatures of 0.3°C over 50 years. He had already established a link between this phenomenon and the increase in atmospheric carbon dioxide from coal combustion. Here we are, 80 years later, and the situation is absolutely terrifying. The last two years have shattered heat records since measurements began in the 19th century, bringing us very dangerously close to the fateful mark of +1.5°C compared to the pre-industrial era. And the pace does not calm down, quite the contrary.
A dizzying acceleration of the global thermometer
The story of global warming is one of inexorable acceleration. If the first level of +0.3° C took an entire century, the mercury has since risen by an additional degree in just sixty years. Data collected by thousands of weather stations, satellites and ships converge towards the same conclusion: since 1970, global temperature has increased at a stable rate of +0.2°C per decadea maddening pace that is completely unprecedented in climate annals.
Heat records recorded over the last two years could even announce a new phase of acceleration. The climate system is extremely complex and has tipping points that we covered in this article. Crossing some of these points could thus lead to irreversible changes and an acceleration of warming.
An overall increase in temperature can also lead to other changes, such as changes in ocean currents or an increase in water vapor in the atmosphere, which in turn can also accelerate warming. A real vicious circle from which we cannot escape, despite our efforts to reduce greenhouse gas emissions.
Greenhouse gases: the big culprits
The pace of global warming today is dictated by our greenhouse gas emissions. The logic is indisputable : the more these emissions increase, the more quickly the planet warms. Conversely, their reduction slows the rate of warming, without stopping it. Only the achievement of absolute zero would stabilize global temperatures.
This mechanism explains the variations observed over the decades, in particular the slight cooling preceding 1970, caused by the accumulation of reflective aerosols from the combustion of fossil fuels. A phenomenon slowed down by policies to combat air pollution in the 1960s.
The many faces of the climate crisis
The heat is not distributed equitably across the surface of the globe. Land surfaces are experiencing more intense warming than the global average, while oceans are warming more slowly. Water has a much greater heat capacity than land. This therefore means that it takes longer to heat up and cool down. The oceans therefore act as “ moderators » of the climate, capable of absorbing temperature variations more effectively.
The Arctic, a very fragile ecosystem, constitutes the hotspot par excellence, with temperatures climbing up to four times faster than the global average.
Concerning the prospects for 2025, climatologists suggest a possible thermal lull. This forecast is based on the emergence of a well-identified natural phenomenon: La Niña. This phase of the El Niño-Southern Oscillation (ENSO) climate cycle in the tropical Pacific Ocean is characterized by a cooling of surface waters in the tropical Pacific. This cooling affects global atmospheric circulations, which can lead to a temporary drop in average temperatures on a global scale.
However, the respite will be very short-lived and the threshold of +1.5°C will be crossed now appears to us to be inevitable. The political and industrial decisions of the coming years will therefore prove decisive. Two scenarios emerge : succeed in limiting the rise in temperatures to between 1.6° C and 1.7° C above pre-industrial levels, or see the thermometer continue to rise. In the latter case, humanity will shift towards hotter horizons with more severe consequences.
- Global temperature has increased by +1.2°C since the pre-industrial era, with an alarming acceleration since 1970.
- Human emissions are the main cause of warming, and only a zero emissions target would stabilize temperatures.
- Without rapid action, the threshold of +1.5°C will be crossed, leading to irreversible climatic consequences.
