Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and Mitsubishi Estate jointly developed the software that estimates warming of cities around the world. Using the supercomputer technology, the software shows the areas that tend to be hot, such as high-rise building area and shopping area, in color image. Besides the two organizations, Building Research Institute and the Tokyo metropolitan government helped the development. The development team combined the supercomputer called “Earth Simulator” that JAMSTEC uses to estimate global warming and Google Earth that is the world map service Google provides on the Internet. The newly-developed software can estimate minutely how hot it is in summer and how warm air flows depending on the direction of the wind in any cities of the world as long as data on such items as amount of exhaust heat of buildings and traffic volume are available. The development team created the moving image of an area of 3 km by 3 km of the business district in Tokyo to show the temperature change in summer. It is possible to see the warm air generated on the heated pavement flowing in whirls from any angles on the PC. The software is expected to be helpful to verification of the cooling effect of urban greening and planning of urban development with few sweltering nights.