Looking at that list, notice how many states with colder climates are in the top 15 happiest: North and South Dakota, Minnesota, Montana, Alaska, Vermont . . while not as far north, some pretty cold-winter and sparsely populated states (Kansas, Nebraska, Iowa) are also said to be happy places. Obviously (to me) something other than climate makes the people in a locale feel more or less happy.
Yes, North Dakota has job growth, and more people working and earning pasychecks could tend to help one's disposition. Contrast that with some of the states toward the bottom third of the rankings . . Great Lakes states like Michigan, Ohio, Illinois and Indiana that have seen their manufacturing jobs dwindle. Something else that I thinks goes along with job losses is people reliance upon drugs to deal with life, and crimes that both follow from negative emotional states and to finance both one's living costs and drug expenses.
Here in Ohio, there is a lot of drug abuse and trafficing, and a lot of violence and property crimes. Unemployed and otherwise messed-up Ohioans are robbing, burglarizing, car-jacking, pimping/prostituting, dope dealing and anything else they can think of to get money. Vacant homes are common, and any house that is vacant for long is going to get stripped of windows, doors, plumbing and other fixtures, and then fires set until there is no alternative but for the city to tear it down. Then, while Ohio has a lot of universities, young people cannot find career-type jobs here like they used to and must leave Ohio in order to pursue careers.
To me, my hometown and home state ARE depressing . . as much as anything because I remember when things were good here, and it saddens me to see how far conditions have declined. I used to think, "Why would I leave Ohio? Everything I need is right here." But now I think, "Why would anyone come to or stay in Ohio? Things just keep getting worse all the time." I especially think this every time I hear of more job loses and more companies closing or moving elsewhere. The cold weather doesn't bother me half as much as the deterioration of conditions.
Yet, I stay . . because my people, dwindling though they are, are here. And, I think places like Ohio are the microcosm of America: when my region declines, the nation declines, and if my nation is to thrive, places such as where I come from need to thrive again.