Monday, 3 July 2023 may have been the hottest day ever on Earth. This is what the U.S. National Centers for Environmental Prediction has said. According to data collected worldwide, the average global temperature reached 17.01°C, surpassing the previous record of August 2016, which was 16.92°C. The measurement was the highest since the beginning of instrumental measurements dating back to the late 19th century. A temperature of 17 degrees may not seem much, but let us not forget that this is an average reading, combining measurements from the northern hemisphere and the southern hemisphere, where it is currently winter. It is true that it has rained a lot in Italy, but in China there have been heat waves above 35°C and in North Africa, where temperatures have repeatedly been close to 50°C. And then Quebec in Canada, Peru, and cities in the southern United States. Even in Antarctica, where it is currently winter, 'extreme' temperatures have been recorded, with peaks of 8.7°C in early July. But what makes this situation so special? Scientists say there are two main causes: the activation of the natural El Niño phenomenon affecting the surface layers of the Pacific Ocean and greenhouse gas emissions.