Sir, - It was encouraging to read (The Irish Times, November 14th) that the Minister for the Environment, Mr Dempsey, pointed out at an ESRI conference that climate change is probably the greatest environmental threat and a critical test of our commitment to sustainable development.The main contributor to climate change is the release of carbon dioxide into the atmosphere from the combustion of fossil fuels. the ESRI conference discussed the problems of emissions to the environment from traffic, industry and the agriculture sector. However 50 per cent of the carbon dioxide emissions is due to the energy used to heat, light and aircondition our buildings. It is surprising, therefore, that the largest contributor to climate change, i.e. the built environment, was not discussed at the conference.It will be interesting to see if the consultancy study commissioned by the Minister's Department to examine existing policies and identify additional measures at national level to limit these emissions will have considered the largest contributor to climate change. - Yours, etc.,K. H. Beattie,Dublin Institute of Technology,Bolton Street,Dublin 1.