Humans have always been affected by Earth’s environment. However, our risk of harm from environmental hazards may be increasing, as research shows extreme heat events are likely to intensify and occur more often across the globe. Extreme heat events are already of particular concern because of Arizona’s dangerously hot summers. Observed warming trends and the projections summarized in this report suggest that some Arizona counties may see warming of up to 4.5 °F above current temperatures by 2060. These trends could affect air quality and human health. Some models suggest that future rises in temperature may also coincide with increases in droughts, flooding, wildfires, and other severe weather events. Some of the most intense events could disrupt public infrastructure and civil services, including transportation and communication networks, energy grids and water distribution.