The heat wave affecting nearly 115 million people in more than 15 states is going to intensify significantly before conditions improve. Why it matters: The heat is so severe and long-lasting that it constitutes a deadly threat in many areas, particularly across the Southwest and portions of the West. Extreme heat is the top annual weather-related killer in the U.S. and can cause harm indiscriminately and quickly. Human-caused climate change is worsening this heat wave by making it more intense, longer-lasting and more likely to occur. An initial analysis from research and communications nonprofit Climate Central ... (full story)