Extreme heat is defined from a baseline of average temperature in any given location, which varies widely around the world. So a temperature of 25 degrees Celsius (77 degrees Fahrenheit) might be record-breaking in some parts of Canada in the spring, but below average in the Middle East for the same period.  "The root of the problem is greenhouse gases that trap heat," said Martin Jucker, a lecturer at the University of New South Wales' Centre for Climate Change Research. Gases like carbon dioxide , methane and nitrous oxide they play a key role in preventing heat from being reflected or lost from our atmosphere. (Sara HUSSEIN)