Although the changing climate is making heat waves more intense and cold snaps less severe, people may not perceive the magnitude of the shift. New research draws on social media posts to reveal that people base their perceptions of what constitutes normal weather on what they've experienced in the previous two to eight years.

The research, which was led by the University of California, Davis, and included Flavio Lehner, a scientist at the National Center for Atmospheric Research (NCAR), analyzed more than 2 billion geolocated tweets from 2014 to 2016 to gauge how people's perceptions of weather changes over time.

The pattern of tweets indicated that people begin to perceive unusually hot or cold temperatures as normal within a short period, even if temperatures had actually changed significantly over time.

"Even if it keeps getting warmer, people appear to adjust their expectations relatively quickly, almost as quickly as the warming itself," Lehner said. "This goes for both heat waves and cold snaps: people today might tweet about a winter day being exceptionally cold, even if the data show that this would have been a perfectly normal temperature a few decades ago."

The study also found that people's responses to unpleasant temperatures did not change, even when they perceived those temperatures as normal. An unusually high temperature, for example, can still cause discomfort, even when expected. The authors liken this to the "boiling frog" metaphor, which describes a frog not jumping out of slowly warming water, even though the increasing heat eventually causes harm.

Lehner emphasized that the research focused only on temperatures. Other types of weather change, such as increases in severe storms and flooding, may not be readily perceived as normal.

The study was published today in the journal Proceedings of the National Academy of Sciences. Funders included the National Science Foundation, which sponsors NCAR.

See the University of California, Davis, news release.

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