Hundreds of thousands of mobile phone users will receive messages from Friends of the Earth this summer urging them to set their air conditioners to 25 degrees Celsius. The environmental group has joined forces with mobile phone companies Hutchison and Sunday in a move to relieve the city of its reputation for having the coldest offices in the world. Throughout the summer, Sunday will send the message four times to remind its 660,000 customers to turn up their air conditioners, while Hutchison will send it in batches of 30,000 to its 270,000 customers. The message reads: 'Save energy and set your air con at 25C - a comfortable, energy-efficient temperature (From Friends of the Earth - HK)'. The mass messaging is part of the group's 'Don't Be Cold, Be Cool' campaign aimed at raising public awareness of 'a bizarre cultural phenomenon in Hong Kong where people turn down the air conditioner and dress up for the artificially cold weather'. A study by Polytechnic University showed 90 per cent of the city's offices averaged between 21C and 23C. Some local offices were found to be as cold as 17C. Friends of the Earth has also launched a 'Thermal Crime' campaign to urge people to report the biggest air-conditioning offenders. Complaints received to date include one from Wan Chai District Council chairwoman Wong ying-kay, who said she had been 'frozen to death' in the Hong Kong Arts Centre cinema. A member of Friends of the Earth said the thermostat at the Hong Kong Medical Association office had been set to 18 degrees. Friends of the Earth environmental affairs officer Agnes Chen Ying-hoi said: 'Friends of the Earth will publicise a list of thermal criminals during summer as an effort to redress cold indoor environments and empower the victims.'