It is in cities that the negative impacts of a warming climate will be felt most strongly. The summer time comfort and well-being of the urban population will become increasingly compromised under future scenarios for climate change and urbanisation. In contrast to rural areas, where night-time relief from high daytime temperatures occurs as heat is lost to the sky, the city environment stores and traps heat and offers little respite from high temperatures. This urban heat island effect is responsible for temperature differences of up to 7 degrees C between cities and the country in the UK. We already have experience of the potential hazards of these higher temperatures. The majority of heat-related fatalities during the summer of 2003 were in urban areas. This means that the cooling of the urban environment is a high priority for urban planners and designers. Proven ways of doing this include altering the urban microclimate by modifying its heat absorption and emission, for example through urban greening, the use of high-reflectivity materials, and by increasing openness to allow cooling winds. Buildings themselves can also deliver improved comfort and higher levels of sustainability by taking advantage of exemplary facade, glazing and ventilation designs. In addition, changed behaviour by building occupants can help keep urban areas cool. The technology to reduce the future vulnerability of city dwellers to thermal discomfort is already largely in existence, But there is a need for complementary policy and planning commitments to manage its implementation, especially in existing buildings and urban areas. (C) 2008 Queen's Printer and Controller of HMSO. Published by Elsevier Ltd. All rights reserved.