In a cafe recently, someone described their toast as "awesome." The bristling that followed wasn't about the toast - nobody tasted it - but about what the word has become. "Awesome" once meant inspiring awe: towering mountains, the vastness of the night sky, the haunting song of a humpback whale. Now it means breakfast.

"Fantastic" has suffered the same fate, shedding its fantastical origins to become a synonym for "great." And "literally" has been abused so thoroughly that it can now mean something that is, quite literally, not literal. Linguists call this "semantic bleaching": the gradual erosion of a word's original meaning through overuse.

Which brings us to another word we hear with increasing frequency: "unprecedented," the go-to adjective in climate reporting. In recent months, there has been unprecedented heat, unprecedented rain, unprecedented drought and unprecedented wildfires. Reports suggest the current El Niño will be - you guessed it - unprecedented. The dictionary definition hasn't changed: it still means something that has never happened before. And all these events genuinely represent a ratcheting up of severity. But the word is used so often it's losing its punch. The extraordinary is starting to sound ordinary, the unprecedented almost routine.

There is nothing ordinary about what's happening. Britain has just experienced its hottest summer on record, beating the previous record set only last year. When climate records keep being smashed, a question arises: what do we actually find remarkable?

In a study analysing more than 2bn weather-related social-media posts, Frances Moore from the University of California, Davis, and colleagues found that for temperature, remarkability changes with repeated exposure. Unprecedented temperatures feel less remarkable when we've experienced similar ones in the previous few years. We judge based not on historical precedents or childhood memories, but on what we've lived through recently. Something can be historically unprecedented but psychologically precedented.

Our yardstick for normal or remarkable is constantly changing. Ecologists call this "shifting baseline syndrome," originally described in fisheries, when Daniel Pauly noted successive generations of fisheries scientists accepted increasingly depleted fish populations as their baseline. The phenomenon is now recognised as widespread - applying to biodiversity loss, pollution, environmental degradation and the climate crisis.

Moore's study had a twist. Although extreme temperatures became less remarkable with repeated exposure, the negative feelings they provoked didn't fade. We may stop finding unprecedented temperatures remarkable, but that doesn't mean we find them tolerable. We're not necessarily becoming blasé about the climate crisis. We can still recognise something is unpleasant without realising how unusual it is.

You've probably heard the parable of the boiling frog: placed in a pot of slowly warming water, the amphibian supposedly fails to notice and stays put until it croaks. Here we all are, bobbing around in our family-size Le Creusets, marvelling at how balmy the water feels while complaining that we're starting to poach. That's the dangerous bit. If extreme temperatures become familiar, we may be less likely to recognise how extraordinary they are. What once seemed remarkable becomes just another hot summer, another flooded street, another crop failure. The baseline shifts - and with it our sense of what needs fixing. If the water feels normal, we may be less likely to demand the heat be turned down.

As it turns out, the old parable gets it completely wrong. No healthy frog would sit idly in a warming pan. They feel the heat and respond. When the temperature crosses a threshold, they hop out. So maybe that's the question: if we can no longer recognise how remarkable these uncomfortable temperatures are, what will it take for us to do what the frog does and respond to the heat?

One place to start is with our words. "Awesome" became ordinary because we kept using it for ordinary things - warm bread and marmalade. Climate extremes are different: the events themselves haven't become ordinary, even if our experience of them is more familiar. "Unprecedented" is in danger of becoming a synonym for "really extreme." It shouldn't. The word tells us we have crossed into territory humanity has never experienced before. It's important we retain that historical meaning.

Perhaps the most unsettling thing about a heating world is not that unprecedented weather keeps happening. It's that "unprecedented" is beginning to sound like a perfectly normal thing to say.

Helen Pilcher is a science writer and the author of Life Changing: How Humans Are Altering Life on Earth and This Book May Cause Side Effects.