The Harvard neuropsychiatrist John Sharp spends a month with his family each summer on the island of Nantucket, so it was doubly problematic that year after year, halfway through, he'd start to feel inexplicably anxious and grouchy: first because a month on Nantucket isn't exactly anything to complain about, and second because he's a neuropsychiatrist; explaining bad moods is his job. It took much beach-front speculation, he recalls, before he finally made the connection to his teenage self, nervous about the new school year. Deep inside (actually, we can be more specific: in his hippocampus), he was still a frightened schoolboy. His moods were at the mercy of the calendar.

These seasonal emotional shifts – the fillip from the first identifiably warm spring breeze, say, or the sinking feeling induced by shortening late-summer evenings – are such a fixture in our lives that they can become near-invisible. We're slow to attribute our feelings to them, and even psychologists haven't studied them much, two oversights that Sharp's fine new book, The Emotional Calendar, aims to address. As a winter-lover – someone for whom that first spring breeze brings only a stomach-knot of apprehensiveness – I devoured it hungrily for evidence that I'm not a freak (it turns out I am, but that at least I'm not alone).

To those of us not afflicted with seasonal affective disorder, or severe hay fever, calendrical influences might seem like a minor thing. But in fact, as Sharp demonstrates, the progress of the seasons affects us on a multitude of levels. For one thing, there are our personal preferences for heat or cold; then there are the deeply imprinted associations between seasonal weather and traumatic or even just moderately stressful past events, such as Sharp's back-to-school nerves. ("A bit of sensory input from the present," he writes, "when cross-referenced with the brain's hippocampal formation – our encyclopedia of emotional connections based on past experience – can… instantly [prepare] us for a replay of our earlier physiological response.") The power of negative comparisons with the past can make things even worse – whither those glorious summers of childhood? – and that's all even before considering the social pressures to feel a certain way in certain seasons. Summer is supposed to be exuberantly fun, and those of us who prefer the clarifying cold can only mutter about how studies show that riots, domestic violence and murders, among other ills, reliably peak as the thermometer rises.

The phenomenon is particularly acute today, Sharp argues, because we've been lulled into thinking that we've conquered the seasons: in the developed world, most of us can be sure of warm homes year-round, bright lighting on dark nights, and summer fruits and vegetables in winter. Two centuries ago, we'd have known what emotional weather the real weather would bring, and could gradually adapt accordingly; these days it takes us by surprise, if we even make the connection at all. Sharp doesn't propose a one-size-fits-all solution, except that we could make more effort to live in the seasons: to get outside, to eat seasonally, to garden. ("Horticultural therapy" is presently, um, blooming.) And thus to reach, if we're lucky, the state of mind encapsulated by George Santayana, as quoted by Sharp: "To be interested in the changing seasons is a happier state of mind than to be hopelessly in love with spring."

oliver.burkeman@guardian.co.uk
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