More than half the world’s population was born after 1985, which was the last year the Earth was cooler than average. The shift could potentially alter younger generations’ perception of “normal” temperatures.

“Because the last three decades have seen such a significant rise in global and regional temperatures, most people under the age of 30 have not lived in a world without global warming,” said Michel Jarraud, secretary-general of the United Nations’ World Meteorological Organization.

The generational shift could have important implications for policies related to global warming. Jarraud said the global public has to be reminded more frequently that the current rates of temperature increases are unprecedented.

“Heat waves, droughts and extreme floods are more likely to trigger associations with climate change,” said Peter Thorne, a climate researcher at the Nansen Environmental and Remote Sensing Center in Bergen, Norway.

By contrast, gradual increases in temperature tend to go unnoticed and are accepted as normal. Global trends are also harder to perceive because people experience climate on a local level. Even as parts of North America experienced a very cold winter, the overall global warming trend was still evident.

The U.S. National Oceanic and Atmospheric Administration lists February 1985 as the last month when the temperature was below the 20th-century average. The U.N. Population Division estimated that the average world population in 2014 was 29.4 years old. Now half the world’s 7.2 billion population was born after the last cool month (Alister Doyle, Reuters, Aug. 6).