America sizzled through some hot nights last month, enough to make history. Federal meteorologists say the Lower 48 states in July set a record for overnight warmth. The average overnight temperature for the continental United States in July was 63.6 degrees, which is the highest in 128 years of recordkeeping. This matters because cooler temperatures overnight are crucial for people, animals and plants to recover from the warmth of daytime heat waves. In the U.S., the nighttime is warming faster than the daytime. Climate scientists say that’s a signature of human-caused global warming.