Paris and other European cities have been sweltering through an unusually early heatwave this week. The scorching weather that has smashed temperature records across Europe this week shows the growing number and intensity of heat waves on the continent. Europe is the continent that has experienced the fastest warming since 1990, according to data from the US National Oceanic and Atmospheric Administration (NOAA). As cities from Rome to London swelter in the unusually early spell of intense temperatures, here are five things to know about heat waves in 21st-century Europe. Wake-up call 2003 The intense heat wave that hit Western Europe during the first half of August 2003 was a real shock in several countries. The exceptional temperatures endured in France, Italy, Spain, and Portugal led to tens of thousands of deaths: a European study published in 2007 estimated there were 70,000 "additional deaths" in 16 countries during the summer of 2003.…