Global warming shatters records and worries scientists

© Javier Miranda/Unsplash

The beginnings of understanding Climate change dates back to September 1933. That year, American meteorologist Joseph Kincer asked a disarmingly simple question: “Is the climate changing?” train of change ? » This questioning was to 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 an initial response, 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 slow down, quite the contrary.

A dizzying acceleration of the world thermometer

The story of global warming is one of inexorable acceleration. While the first +0.3°C threshold took an entire century, the mercury has since soared by an additional degree in just sixty years. Data collected by thousands of weather stations, satellites and ships converge on the same conclusion: since 1970, global temperature has been increasing at a stable rate of +0.2°C per decade, a frightening pace that is completely unprecedented in climate annals.

The heat records recorded in the last two years could even herald a new phase of acceleration. The climate system is extremely complex and has tipping points that we discussed 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 are unable to escape, despite our efforts to reduce greenhouse gas emissions.

The graph shows an increase significant increase in global temperatures from the 1970s, characterized by an increasingly steep slope. © Ed Hawkins/National Centre for Atmospheric Science

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Greenhouse Gases: The Big Culprits

The Pace of Global Warming Is today dictated by our greenhouse gas emissions. The logic is indisputable: the more these emissions increase, the faster the planet warms. Conversely, their reduction slows the rate of warming, without stopping it. Only reaching absolute zero would stabilize global temperatures.

This mechanism explains the variations observed over the decades, in particular the slight cooling before 1970, caused by the accumulation of reflective aerosols from the combustion of fossil fuels. A phenomenon slowed down by the policies to combat air pollution in the 1960s.

The many faces of the climate crisis

Heat is not distributed equitably across the globe. Land areas are warming more intensely than the global average, while oceans are warming more slowly. Water has a much higher heat capacity than land. This means that it takes longer to heat up and cool down. Oceans therefore act as “moderators” of the climate, capable of absorbing temperature variations more efficiently.

The Arctic, a very fragile ecosystem, is the hot spot par excellence, with temperatures rising up to four times faster than the global average.

Concerning the outlook for 2025, climatologists advance 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 circulation, which can lead to a temporary drop in average temperatures on a global scale.

However, the respite will be very short-lived and crossing the +1.5°C threshold now seems inevitable. The political and industrial decisions of the coming years will therefore prove decisive. Two scenarios are emerging: managing to limit the rise in temperatures to between 1.6°C and 1.7°C above pre-industrial levels, or seeing the thermometer continue its rise. In the latter case, humanity will tip towards hotter horizons with more severe consequences.

• Global temperatures have 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 +1.5°C threshold will be crossed, leading to irreversible climate consequences.

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