A Curious Link Between Seasonal Heat, Depression, and Mania
The effect of warm temps on depression might be more complicated than we thought.
Posted December 12, 2025 | Reviewed by Monica Vilhauer Ph.D.
Winter weather is in full effect in many parts of the United States, exciting many who love a cozy, white Christmas or snow sports, and upsetting those who miss having more daylight and warmer temperatures. For the latter group, unseasonably warm days might feel like a much needed reprieve. However, things appear a bit more complicated for those experiencing symptoms of depression or mania .
A 2025 study in the Journal of Affective Disorders by Philippa Clery and colleagues showed some surprising seasonally-dependent effects of elevated ambient temperatures. Unexpectedly, warmer temperatures in winter did not improve depression symptoms, and in some cases, they appeared to make them slightly worse!
The researchers who conducted this study used an approach called ecological momentary assessment, or EMA. Around 4000 participants with depressive symptoms and over 2000 with mania symptoms responded to questions and surveys on a mobile app. The surveys included validated clinical assessments of bipolar and depression symptoms and were linked to the meteorological conditions where each participant completed the surveys for the preceding 2 weeks.
Based on prior studies documenting an increase in psychiatric hospitalizations with elevated temperatures in the summertime, the team hypothesized that hotter temperatures would worsen depression and mania symptoms. However, they also sought to investigate several key factors that might influence this relationship. They looked at different ways to quantify temperature (average daily temperature vs. maximum daily temperature), whether the effects differed across seasons, and whether it mattered if the temperature was different from ‘typical’ weather conditions in the area at that time.
Mania spikes in warmer weather, but depression is more complicated
As expected, participants with bipolar disorder reported more manic symptoms with warmer temperatures, and the effects didn’t differ much by season. These effects also held when controlling for participant gender and other related weather effects, like sunshine and air pollution. When the researchers examined changes in heat relative to the normal weather conditions, they found the same effect — warmer ambient temperatures led to more mania symptoms.
Counter to the researchers’ hypotheses, warmer temperatures led to fewer depressive symptoms, particularly in the spring and summer. More surprisingly, when accounting for typical temperatures, the effects of unseasonably warm winter days actually showed an increase in depression.
Though this study cannot test why warmer weather causes these effects, there are some promising mechanisms — at least for why heat increases mania. Specifically, increases in temperature affect key neurotransmitters, like serotonin, which can impact both manic and depressive symptoms. Additionally, sleep is known to impact mood disorder symptoms, and there is increasing evidence for the toll that heat takes on sleep quality (Minor et al. 2022).
As for the effects on depression? Well, this is where things are much less clear. These results aren’t consistent with what most prior research has found, so it’s hard to know exactly what is going on here. A few points to consider are that the researchers are using outdoor temperature as their estimates for heat exposure. Depending on the use of indoor heating and cooling systems, and time spent indoors vs. outdoors, this may not match actual exposures.
Beyond this, most of the research that has looked at changes in mood with higher temperatures hasn’t focused specifically on individuals with depression or bipolar disorder. So the effects might be different for those with a diagnosed condition compared to those who experience subclinical symptoms. Ultimately, much more research is needed to identify what is going on, and why unseasonably warm days might not have mood-boosting benefits for individuals with depression.
In the meantime, might I recommend spending some quality time outside, noticing the natural world around us? Maybe give this exercise a try — according to a 2022 study by Passmore et al. , it seems like the mood boosting effects of noticing nature work just as well in the cold winter months as they do in warmer weather!
Clery, P., Hayes, J. F., Launders, N., Thompson, R., Kandola, A., Osborn, D. P. J., Lawrance, E. L., Jeffery, A., & Dykxhoorn, J. (2025). The association between outdoor ambient temperature and depression and mania: An ecological momentary assessment study. Journal of Affective Disorders, 379, 457–466. https://doi.org/10.1016/j.jad.2025.03.046
Minor, K., Bjerre-Nielsen, A., Jonasdottir, S. S., Lehmann, S., & Obradovich, N. (2022). Rising temperatures erode human sleep globally. One Earth, 5(5), 534–549. https://doi.org/10.1016/j.oneear.2022.04.008
Passmore, H.-A., Yargeau, A., & Blench, J. (2022). Wellbeing in winter: Testing the Noticing Nature Intervention during winter months. Frontiers in Psychology, 13, 840273. https://doi.org/10.3389/fpsyg.2022.840273
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Kim Meidenbauer, Ph.D. , is an assistant professor of psychology at Washington State University and a member of the WSU Health Equity Research Center.
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This article is part of the Bringwise Psychology Journal — daily insights on human behavior, mental health, and personal growth.