How do we know that climate change is caused by humans?

How do we know that climate change is caused by humans?

This message comes from the newsletter “Human Warmth”, sent every Tuesday at noon. Every week, journalist Nabil Wakim, host of the Chaleur Humaine podcast, answers questions from internet users about the climate challenge. You can register for free here:

The question of the week

“Hello, I have a rather basic question, but I can’t find the answer in your podcasts. How do we know that it is humans who are warming the climate and not a classic variant as in the past? I’m not a climate skeptic, but it’s an argument people often throw at me. Thank you “ (Question asked by Patrice at chaud humaine@lemonde.fr.)

This week it is my colleague Ynès Khoudi, who works in the Planète du Worldwhich answers your question.

Response from Ynes Khoudi:
Hello Patrice, thank you for your question. It is true that climate is influenced by many factors. But human origins, “anthropogenic”According to scientists, current global warming is now beyond question for all scientists working on this subject. (You can find a great infographic from Les Décoders about how humans are warming the planet here)

1/ How do we measure global warming?

Scientists have various means at their disposal to measure CO levels2 or methane in the atmosphere. For example, with satellites in space or even thanks to ice, which encloses small air bubbles and eventually becomes completely isolated from the atmosphere, making it possible to analyze traces of CO2 out there (on this subject, you can read this incredible article here about how French glaciologist Claude Lorius first understood the influence of greenhouse gases on the climate). Certain methods allow us to go back even further in time, for example the analysis of paleosols, these burials, old and inactive soils, or the observation of marine sediments or tree rings.

Almost all studies published on this topic agree on the rate of current warming and its human origins.

The tilt of the Earth relative to the sun or volcanic eruptions are common arguments used by climate skeptics or the oil industry to support the idea of ​​global warming. ” Naturally “ Or “normal” (If you’re interested, I recommend the book The merchants of doubt, by Naomi Oreskes and Erik M. Conway (Ed. Le Pommier, 2012). If these factors have indeed played a role in climate fluctuations throughout history, these arguments are not serious to qualify current warming: it is happening much too fast. Since the mid-19th centurye In this century, the planet has warmed by about one degree and sea level rise since 1900 has been faster than in three thousand years. Current temperatures are the highest in a hundred thousand years and CO2 levels2 present in the atmosphere is the highest in 14 million years. Temperature records have been broken every year since 2000, both on land and in the ocean. (See how temperature records are defined here.)

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