Just look at what 1.4 degrees Celsius of warming has done: higher average and extreme heat, more intense storms and more fuel for wildfires, hotter and higher seas, warmer summers and winters. Many animals and plants are shifting to new areas, seeking familiar ecosystems where they can find them. Industries and economies are increasingly facing impacts costly in damage or even lives.
This number matters because every small fraction of a degree matters. The Paris Agreement in 2015 set a worldwide aspirational target to hold warming to 1.5°C, or no more than 2°C. With the 1.5°C target out of reach and the US abandoning the pact, the global conversation is losing a unifying, simple-sounding goal — one that would have prevented hundreds of millions of people from suffering through extreme heat waves.
No one directly experiences the global average temperature. It’s a way for scientists to analyze and communicate how much energy the Earth is trapping that would have radiated into space without climate pollution. Scientists don’t compile temperature records the way you’d eyeball a thermometer. A difference so slight it would have no bearing on your decision to wear a coat in the morning—more than 1°C above the 20th century average—ends up having far-reaching climate consequences.
Scientists know that human activity is causing the world to heat up. The UN-backed Intergovernmental Panel on Climate Change confirmed human influence on the temperature in the mid-1990s and today call it “unequivocal.”
Readings from the thousands of land- and sea-surface monitors are reported as the difference (or “anomaly”) from the monitor’s own long-term record. The raw data come from weather-monitoring stations, ships, buoys and satellites. These anomalies are then analyzed, stripped of biases and averaged into the larger figure. Several groups analyze temperature records, including the National Oceanic and Atmospheric Administration, NASA Goddard Institute of Space Studies, the U.K. Climate Research Unit, Berkeley Earth and the Japanese Meteorological Agency. The European Union’s Copernicus Climate Change Service keeps a temperature record, based on past weather data run through powerful models.
The rate of warming since 1982—0.36°C per decade—is more than three times the rate since 1880. A sign of progress in the worldwide effort to cut out greenhouse-gas emissions would be a slowing of this rate of rising temperatures. The good news, such as it is: When greenhouse gas emissions stop, so will global heating.