Hong Kong has forgotten all about the government's campaign to set air conditioners to 25.5 degrees Celsius.
A survey by Green Sense found more and more establishments were cranking their air conditioning to as low as 17 degrees.
'Refrigerator' malls and offices are back, causing long-term environmental damage and health problems, the green group warned.
It received 37 complaints in June about Arctic indoor temperatures - double the number from the same month last year.
Checks on 22 commercial locations found all had temperatures below 25 degrees, with the interior of one commercial building in Kwun Tong registering 17 degrees.
'It's so unnatural to have to put on jackets indoors because of cold air conditioning while outside temperatures are well over 30 degrees,' Green Sense project manager Gabrielle Ho Ka-po said, holding up a photo she had taken on the MTR's Tung Chung line showing two overseas tourists donning jackets upon stepping into a train. The group received four complaints about trains on that line being too-cold. It found the temperatures ranged from 20.8 to 21.8 degrees.
An MTR spokesman disputed the finding, saying all the trains were programmed to stay at 26 degrees, with sensors monitoring and adjusting the temperature.
Leung Wing-mo, assistant director of the Observatory, said air conditioning was an indirect but major contributor to global warming in Hong Kong and nearby regions. He said most air-conditioning systems in the city emitted hot fumes, aggravating the already hot summer.
'If we don't curb our energy consumption now, it will cause great damage in the future - including serious flooding, extreme weather conditions and rises in sea levels,' he said.
'This will ultimately destroy our homes and even cut our food supply.'
Physician Dr Betty Kwan Ka-mei said overly cold air conditioning could cause serious health problems, such as a weakening of the immune system, making people more susceptible to the cold.
'People used to catch a cold in the winter, when it's cold,' she said. 'Now, I've received more and more people in the summer with cold symptoms or sinus problems - mainly due to being inside cold air conditioned rooms most of the time.'
Kwan said the huge gap between indoor and outdoor temperatures - sometimes over 10 degrees - was one reason people were getting sick.