Too Much Rain Is Now a Major Chocolate Climate Threat

For years, the climate conversation about chocolate centred on heat and drought. A new Chocolate Climate Threat is shifting that picture: heavy rain falling at exactly the wrong moment can do as much damage to a cacao crop as a dry spell, according to researchers at Harvard and a partner university in Ghana who studied two decades of district-level harvest records.

The team found that wet-season downpours, combined with dry-season drought, explain about two-thirds of the year-to-year swings in Ghana's cacao output. That finding matters far beyond one country, because Ghana and its neighbour Côte d'Ivoire together produce close to half of the world's cocoa, and the beans they grow end up in bars, drinks and baked goods eaten on every continent.

Why timing matters more than averages

Cacao trees live for decades, and a good harvest depends on a long chain of events: flowering, pollination and pod growth. Rain that arrives while trees are flowering can batter the blossoms and help fungal disease spread to young pods, while a lack of rain later, as pods keep developing, can shrink the crop that survives. Averages hide that danger, the researchers argue, because a season can look normal on paper while containing a few destructive bursts.

In Ghana, the most damaging rains tend to fall during the April-to-June wet season, when trees are flowering and young pods are forming. The dry stretch from November to February brings the opposite risk, as too little rain while pods mature can cut yields again. The study tested those swings against daily weather records and a long list of possible causes, from average rainfall and soil moisture to temperature extremes, and the two seasonal rainfall patterns came out on top.

The pattern was not unique to one country. When the team checked two other major producers on different continents, Ecuador and Indonesia, years with heavier wet-season rain also tended to be worse for cacao. That cross-check is one reason the researchers believe the lesson travels, even though local soils, varieties and farming practices differ.

What farmers can do, and why shoppers feel it

Because cacao is vulnerable only at particular stages, protection has to be timed carefully. The researchers suggest that more canopy cover could shield flowers from large raindrops, and that keeping leaf litter on the ground could stop splashes carrying infection from soil to pods. Disease control timed around forecast downpours could help too, if warnings arrive early enough for growers to act.

Forecasting may be the most practical payoff. The damaging rains are linked to large-scale patterns such as El Niño and shifts in Atlantic sea-surface temperatures, so some bad years could be flagged months ahead. A strong El Niño now developing typically favours heavy rain in coastal Ecuador and drier weather across the West African producing belt and Indonesia, a contrast that shows why a single global forecast is never enough.

Shoppers have already felt the knock-on effects of volatile harvests. Raw cacao prices tripled in 2024, as a public radio report on the findings notes, and the squeeze showed up as higher shelf prices, smaller bars and recipes reformulated to use less chocolate. Similar weather shocks elsewhere have tested how cities cope with a changing climate, as recent storm preparations in India showed, and as urban tree planting has tried to blunt rising heat.

There are limits to what rainfall alone can explain. The authors note that ageing trees, gold mining, smuggling, fertiliser costs, pests and disease can all pull production down, and that rain gauges do not always capture the fiercest downpours, which are precisely the events that matter most. Climate models also struggle to represent rainfall patterns over the producing region, let alone how they will shift in coming decades, so the Chocolate Climate Threat will need better local data as well as better forecasts.

For growers, the message is more hopeful than it first sounds. If the riskiest weeks can be predicted, a warning issued before flowering could let a farming community prune, protect and time treatments while there is still a crop to save. For everyone else, it is a reminder that the price of a bar reflects weather in a few coastal farming districts thousands of miles away, and that even well-meant warnings only help when people can act on them. The next step for this Chocolate Climate Threat research is turning a seasonal outlook into a warning a farmer can use.