A dog in Delta K9 Academy's training program.Mike Israeli A new study from Harvard analyzed almost 70,000 reports of dogs biting humans in the US. The study showed that incidents of dogs biting humans increased in line with rising temperatures. It also increased with higher UV levels and on days when certain types of pollution were high. Dogs can be more aggressive on hot, sunny, and smoggy days, according to a new study that analyzed almost 70,000 US reports of dogs biting humans.