We've been warned that our planet will change in unimaginable ways if we don't act soon, and new research shows nearly 50 percent of 15–84-year-olds have already experienced significant change.

Seeing what lies ahead, climate scientists have been at pains to show us how climate change will intensify such that today's youth will bear the brunt of climate impacts in years to come.

Yet all over the world, people are already witnessing extreme and deadly weather events fueled by rising temperatures that once seemed unfathomable.

So just how much climate change have people already experienced in their lifetimes? And who has weathered the most warming so far?

Those are the questions Andrew King, a climate scientist studying extreme events at the University of Melbourne, Australia, and his colleagues set out to answer in a new study.

In local temperature records, they looked for a clear signal of human-caused climate change emerging from the background noise of shifting weather patterns.

As past research shows, signals of human-induced warming have emerged earlier and stronger in the tropics, while the world's oceans and polar regions have absorbed much of the heat.

King and colleagues wanted to add to those analyses by examining people's experiences of local temperature changes up to 2021 and computing those changes in a timeframe everyone can understand: their lifetime.

"It's important we understand people's experience of climate change locally to see who is most affected by the changes that humanity's greenhouse gas emissions are causing to the planet," King told ScienceAlert.

To avoid recollection bias, the researchers calculated the physical warming people have experienced in their local area, not the broader changes they might have perceived.

They also only quantified local warming, not the impacts of prolonged heatwaves, sea-level rise, storms, droughts, and wildfires – though that could be the focus of future work, King says.

"This is the first analysis that attempts to estimate the emergence of local climate change signals experienced by the population of the world, young and old, rich and poor," King and colleagues write in their paper.

Local annual temperatures have changed so much for the global population that the analysis found almost half of the world's 15–84-year-olds are now experiencing an 'unfamiliar' climate that is significantly different from when they were born.

Nearly 90 percent have experienced temperature changes that equate to an 'unusual' climate.

"We need to do more work to see if this also means they've experienced stronger changes in extremes like heatwaves and to better understand whether the worst impacts line up with the biggest climate changes," King told ScienceAlert.

As for age groups, the analysis found middle-aged people between 40 and 60 years old, particularly those living around the equator, have experienced the clearest signal of warming, accrued over their lifetime.

The signal in older age groups was diluted by their early life years of relative climate stability, while younger people's experience of warming varies greatly depending on where they live.

Those living in tropical areas have, worryingly, weathered about the same amount of warming in their much shorter lifetimes as older, wealthier populations.

"It was really remarkable to find that even with a much more youthful population in tropical low-income regions, the typical experience of warming is, on average, similar to the experience of wealthier regions with much older populations," King said.

While some of us have lived on this planet longer than others, the point of the study isn't to point fingers but to convey just how fast Earth's climate is now changing. But we know we can stabilize the climate if we slash emissions.

"It's imperative that substantial climate action is taken to avoid local climates becoming unrecognizable within human lifetimes," the researchers conclude.

The study has been accepted for publication in the journal Environmental Research Climate.