Image copyright Getty Images Image caption The summer of 2015 saw severe heat waves over Europe for the third time in 15 years
The past 30 years in Europe have likely been the warmest in more than two millennia, according to new research.
The study used tree ring records and historical documents to reconstruct yearly temperatures going back 2,100 years.
Scientists say that past natural variability in temperatures was greater than previously thought.
As a result, climate models may be underestimating the frequency and severity of heat waves in the future.
According to the study, Europe has seen an increase in summer warming of 1.3C between 1986 and 2015.
In this period there has also been an increase in severe heat waves, most notably in 2003, 2010 and 2015.
The 2003 event was linked to the extra deaths of thousands of elderly people due to heat stroke, dehydration and increased air pollution.
Extending the record
In 2014, researchers from the Intergovernmental Panel on Climate Change found that the period between 1983 and 2012 was likely the warmest 30 years of the last 1,400 in the Northern Hemisphere.