Air conditioning has been a big life saver in the United States in the past 50 years and could prove to have the same benefit worldwide, a study indicates. Researchers from Tulane University, Carnegie Mellon University, the National Bureau of Economic Research and the Massachusetts Institute of Technology took a look at heat-related deaths in the United States between 1900 and 2004 and found that days when it got hotter than 90 degrees Fahrenheit there were about 600 premature deaths annually between 1960 and 2004. They said that was about one-sixth as many deaths as would have occurred during the 1904-60 period before most homes were cooled by air conditioning, The Washington Post reported Saturday. \"It\'s all due to air conditioning,\" MIT environmental economics Professor Michael Greenstone, one of the paper\'s co-authors, said. The researchers said they found the likelihood of premature death on an extremely hot day between 1929 and 1959 was 2.5 percent. From 1960 on, it dropped to less than 0.5 percent. The researchers\' findings are under review at an academic journal, the Post said. The newspaper said the study\'s results could be important for nations such as India where home air conditioning is relatively rare. Anand Patwardhan, a visiting professor at the School of Public Policy at the University of Maryland, said he expects home air conditioning to become more common in India. \"While it is certainly the case that residential air-conditioning helps in reducing mortality due to temperature extremes, the rapid growth of air-conditioning in the past is perhaps more due to rising incomes and increasing affordability of air-conditioning,\" he wrote in an email. The spread of air conditioning has one obvious problem, Greenstone noted, since many of these units will likely be powered by fossil fuels and will therefore increase the world\'s carbon output. Andrew Steer, president of the World Resources Institute, said while \"air conditioning [is] growing in leaps and bounds in developing countries with rising temperatures,\" policymakers should explore \"ecological\" adaptation strategies that are more ecologically friendly.