<p>Plumes of calcite (limestone) in the air can be created to cool cities. The radiant properties of calcite are ideal for reflecting solar radiation while allowing ground radiation to pass through. Las Vegas is a suitable location since local limestone is available, the region experiences much sunshine daily, and air conditioning is extensively used. Calcite would be dispersed into the air from a ring of towers around the city. Modeling shows that the aerosol would block half the solar radiation and reduce maximum daily temperatures by 5 to 6 °C. A proposed system would save 38% on air-conditioning energy use and 15% of total yearly energy use in Las Vegas. The savings cover the costs for operation of the proposed system plus financing of the capital expense. The simple payback time of the capital expense is within 4 to 6 years. Accounting for improvements in health and tourism could result in much more rapid payback times. Carbon dioxide emissions are reduced on net if natural gas power generation is incrementally reduced. This type of project is likely to be feasible in other cities that have local light-colored calcite deposits, near universal air conditioning use for half a year or more, and dense development</p>