A landmark study of nearly 20,000 toddlers across six countries provides the first large-scale evidence that extreme heat directly impairs the cognitive development of young children, threatening foundational learning skills. The research identified a critical threshold of 32 C (90 F). Children aged 3-4 living in regions where average maximum temperatures regularly exceed this point score significantly lower on tests for basic literacy and numeracy. Young children are biologically vulnerable as their cooling systems are underdeveloped. Prolonged heat exposure can cause dehydration, disrupt sleep, trigger inflammation and release stress hormones, all of which interfere with normal brain maturation. The developmental harm from heat…