Weather Affects Our Moods
I was browsing a blog the other day and saw an undated (recent?) entry suggesting that research shows that “weather has little effect on our mood.” The entry relied heavily on a recent study (Denissen et al., 2008) that shows that although a correlation between mood and weather does exist, it’s a small one (not nearly as large as conventional wisdom might suggest). The entry quotes almost exclusively and entirely from the one study.

I’m familiar with this area of research, so I found the entry’s conclusions a little simplistic and not really doing justice to this topic. There’s a fair amount of research in this area (more than the 3 or 4 studies mentioned in the blog), and I think the overall preponderance of evidence suggests that weather can have more than just a “little effect” on your mood.

Some previous research confirms the blog entry’s conclusion that weather may have little effect on our moods. For instance, Hardt & Gerbershagen (1999) looked at 3,000 chronic pain patients who came to a hospital over a 5-year period. The researchers had patients fill out a depression questionnaire, and then analyzed the results. They found no correlation between depression and the time of the year, nor the amount of daily hours of sunshine. But the researchers only examined depression, and didn’t measure how much time subjects spent outside (a factor that some have suggested might influence how much the weather impacts us).

Other research paints a very different picture.

Howard and Hoffman (1984) had 24 college students keep track of their mood (by filling out a mood questionnaire) over 11 consecutive days. They found a significant effect on mood correlated with the weather, especially with regards to humidity (a component of weather not always measured):

Humidity, temperature, and hours of sunshine had the greatest effect on mood. High levels of humidity lowered scores on concentration while increasing reports of sleepiness. Rising temperatures lowered anxiety and skepticism mood scores. […]

The number of hours of sunshine was found to predict optimism scores significantly. As the number of hours of sunshine increased, optimism scores also increased. […]

Mood scores on the depression and anxiety scales were not predicted by any weather variable.

Another study by Sanders and Brizzolara (1982) on 30 college students also found similar findings — that high humidity was a predictor for lack of vigor, elation, and affection.

But you may dismiss these studies as small, or on unrepresentative samples (college students). You’d have a harder time making that argument against Faust et al.’s (1974) study on 16,000 students in Basle City, Switzerland. Although not the most robust study designed, the researchers nonetheless found that nearly one-third of the girls and one fifth of the boys responded negatively to certain weather conditions. Symptoms reported included poor sleep, irritability, and dysphoric (depressed) mood.

If you noticed that higher humidity is associated with certain mood states, you won’t be surprised to hear there is also a good body of research that has investigated the link between heat and different types of human behavior, especially aggression (see, for example, Rotton & Cohn, 2004; Cohn & Rotton, 2005; Anderson, 1987; etc.). While there’s some debate as to how strong a relationship exists between heat and violence, this is a relationship that been undergoing research since the 1970s. At this point, it’s not in question whether a link exists, just how strong and what the relationship exactly looks like (and whether it’s mediated by other factors, like time of day).