The broad warming observed over the past decades across South Asia is likely to continue into the future. Multi-model projections indicate that mean temperature increases over the area are expected in the range of 2?3�C by 2050 compared to the late 20th century. Human perceived heat?the combination of temperatures with humidity?as expressed through the heat-index is likely to rise by significantly more, possibly 4?7�C, over the same time span. While heat is already an issue for the large fraction of the poor population that suffers from a lack of appropriate shelter and access to basic water and energy, the rapid rise in heat is likely to become an inescapable challenge. As the average daily heat-index reaches human body temperature, lack of cooling will significantly impact economic productivity and pose severely heightened health risks. Although South Asian populations have learned to cope with episodes of heat, future heat events will become relentless as the number of days of excessive heat increases and gaps between heat episodes shrink or even disappear.

Overall, the heat-season will start earlier in the year and last longer into the fall. Both daily and nighttime temperature and heat will reach unprecedented levels that are difficult to escape without access to active cooling. Daily maxima in the late afternoon can possibly be partially ameliorated through construction of simple forms of shade and through the use of evaporative cooling. For rapidly increasing nighttime minimum temperatures, however, which previously provided natural relief, there is no obvious, simple adaptive measure. A form of active but clean, low-energy cooling will be necessary to help the large populations of urban, peri-urban and even rural poor cope with the coming changes without leading to counterproductive increases in greenhouse gas emissions. Keywords: Climate Modeling and Scenario Planning; Extreme Heat; Health; Resilience and Climate Change Adaptation; Social Vulnerability