The increase has been higher in the eastern part of the country, with individual months deviating from the long-term average by up to five degrees, Gregor Vertačnik of ARSO said.

The average atmospheric temperature in Slovenia has increased by 0.34 degrees Celsius per decade. The lowest morning temperature has increased at a faster pace than the highest daily temperature on average.

The data is based on the Fifth Assessment Report by the Intergovernmental Panel on Climate Change and refers to the 1961-2011 period.

A number of environmental NGOs responded to the report, calling on the government to take immediate measures to prevent further atmosphere warming.

"The most important message of this report is that we still have a choice," Nina Štros of Greenpeace Slovenia aid, adding that the country should opt for the potential of renewable energy.

Urška Žmauc of environmental NGO Focus added that the Slovenian government was given a wake-up call. "We expect that it will immediately start addressing the problem," she said.