Data from the University of Maine's Climate Reanalyzer tool, that uses satellite data and computer simulations, showed the earth's average temperature reached 17.18 degrees Celsius on Wednesday.

Even though the dataset used for the unofficial record goes back only to 1979, Dr Kapnick said that given other data, the world is likely seeing the hottest day in “several hundred years that we’ve experienced.”

Scientists generally use much longer measurements — months, years, decades — to track the Earth’s warming. But the daily highs are an indication that climate change is reaching uncharted territory.