As part of their study, Paul Della-Marta and his team compiled evidence from 54 high-quality recording locations from Sweden to Croatia.
They found that the heat waves lasted an average of three days, with some lasting up to 4.5 days compared to an average of around 1.5 days in 1880.
In a nutshell, the length of heat waves on the continent had doubled and the frequency of extremely hot days had nearly tripled in the past century, the researchers said.
"The new data shows that many previous assessments of daily summer temperature change underestimated heat wave events in western Europe by approximately 30 percent," the scientists wrote in their study in the August 3 issue of the Journal of Geophysical Research-Atmospheres.
The researchers said their study contributed to growing evidence that western Europe's climate had become more extreme. The study also confirmed a previously hypothesized increase in the variance of daily summer temperatures since the 19th century.
"These results add more evidence to the belief among climate scientists that western Europe will experience some of the highest environmental and social impacts of climate change and continue to experience devastating hot summers like the summer of 2003 more frequently in the future," Della-Marta said.
"These findings provide observational support to climate modelling studies showing that European summer temperatures are particularly sensitive to global warming. Due to complex reactions between the summer atmosphere and the land, the variability of summer temperatures is expected to [continue to] increase substantially by 2100," he added.