According to international environmental group Greenpeace, high temperature areas in South Korea have more than doubled in the past nine years due to climate change.

About 12 percent of South Korea's land mass saw temperatures exceeding 30 degrees Celsius from 2002 to 2010, the agency said, citing satellite data from the U.S. National Aeronautics and Space Administration(NASA). However, such areas expanded to cover 27 percent of the nation in 2011-2019.

Some 87 percent of the country, with the exception of the Taebaek mountain range in Gangwon Province,  saw the mercury rise from 2011 to 2019.

Surface heat in six percent of the country, including Seoul, rose by more than one-point-five degrees Celsius.

Greenpeace also said six out of eight of the nation's most densely populated cities saw heat waves, or the period of excessive heat at the height of summer when temperatures hover over 30 degrees Celsius, begin some ten days earlier and last longer in the 2001 to 2020 period, compared with the 1981 to 2000 period.

Heat waves began 12-point-seven days and eleven-point-five days earlier in Gwangju, and Busan respectively, followed by Seoul with ten-point-six days and Suwon with nine-point-three days in the cited period.