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).

Keller and his colleagues (2005) examined 605 participants responses in three separate studies to examine the connection between mood states, a person’s thinking and the weather. They found that:

[…P]leasant weather (higher temperature or barometric pressure) was related to higher mood, better memory, and ‘‘broadened’’ cognitive style during the spring as time spent outside increased. The same relationships between mood and weather were not observed during other times of year, and indeed hotter weather was associated with lower mood in the summer.

These results are consistent with findings on seasonal affective disorder, and suggest that pleasant weather improves mood and broadens cognition in the spring because people have been deprived of such weather during the winter.

So while Denissen et al. (2008) found no general ability for the weather itself to lift us into a more positive mood (contrary to both Howard & Hoffman and Keller’s findings above), the researchers did find that the weather can impact our moods negatively. And while that effect in the present study was small, it confirms the same effect found in a multitude of other studies (some of which are mentioned above).

Another way to look at it is that Denissen and colleagues confirmed prior research that showed that people’s moods and emotions can definitely be affected by the weather. The strength of that relationship varies from person to person. But a study’s design has a lot to do with trying to find this relationship in the data. And while Denissen’s design was good, it wasn’t foolproof. Its problems include the over-representation of women in the sample (89%), suggesting a skewed and biased sample, and the response rate, with participants submitting on average half the number of surveys needed by the study’s design. In other words, the data may not be the most robust in the world either (despite the large sample size).

So, sorry, yes, weather does appear to impact our moods. And that effect may become serious. Look no further for evidence of this than the very real condition called Seasonal Affective Disorder (SAD). SAD is characterized by feelings of sadness and depression that occur in the winter months when the temperatures drop and the days grow short. This specific form of depression is often associated with excessive eating or sleeping and weight gain. Women are twice to three times more likely to suffer from the winter blues than men. If SAD is merely a “culturally transmitted idea” (as the blog quotes the researchers as suggesting), then so is every mental disorder to one extent or another.

The new research provides some contradictory data to previous findings. And when such discrepancies arise, the answer is not to conclude the matter settled, but to go and conduct more research. So what Denissen’s study really shows is that more research is needed to better determine the strength of the link, and whether it affects people in different geographical regions (and countries).

So no, you’re not crazy if you think your mood is affected by the weather. Nearly 40 years of research suggests there’s a strong link. And one that, in some people, can lead to significant seasonal problems.

Learn more: Can Weather Affect Your Mood? An Update on the Research

Read the PsyBlog blog entry that got the research wrong: Weather Has Little Effect on Mood