evidence: The relationship between atmospheric CO2 levels and climate change is often perceived as a controversial subject. While there’s no real disagreement among climate scientists – around 90% fully agree that human activity is clearly responsible for climate change – in the United States in 2016, barely 50% of the general public came to the same conclusion. Adding to the general confusion, highly active "climate-change deniers" claim that temperature has evolved independently of CO2 atmospheric concentrations through Earth’s history, and that therefore today’s rising CO2 levels are not an issue. [...] Using rocks, fossils and their chemical and physical properties, geoscientists have reconstructed warm and cold periods throughout Earth’s history. To demonstrate the link between climate, temperature and pCO2 millions of years ago, we need to reconstruct each of them independently. To do so, we use climatic recorders called "proxies". [...] On long time scales, when pCO2 increases, warming stimulates the carbon pumps, thereby helping pCO2 to decrease. This negative feedback can act as a geological thermostat. Unfortunately, it is too slow to react rapidly enough to compensate for our fast emissions. On the timescale of a decade, warming aggravates CO2 release to the atmosphere. When temperature increases, oceans warm up and release dissolved CO2 to the atmosphere. For 2.6 million years, glacial and interglacial cycles have been forced by Earth’s orbital fluctuations and CO2 was only an internal positive feedback. Today, anthropogenic CO2 leads and amplifies the ongoing warming.