COLOMBA, Guatemala — For as long as they can remember, the farmers who grow coffee between the steep volcanic peaks here started the annual harvest in late September — until this year.

An erratic rainy season forced the farmers of the Santa Anita La Union Cooperative in this small town in Guatemala's highlands to start picking coffee in the final days of August.

"Instead of raining constantly and slowly, it is raining very hard for short periods of time. And the temperatures are hotter, so that means the fruit, the coffee, is ripening very fast," said Mynor Huerta, who provides technical assistance to the cooperative, as rain clouds gurgled overhead.

While this year's early harvest may prove to be a climatic anomaly, researchers say that it could be a forecast for coffee in the region.

The same conditions that have made Central America home to some of the world's finest coffees also make it susceptible to the effects of climate change. Its moderate temperatures are already rising, its predictable rainy season is becoming irregular, and pests and fungi could invade altitudes where they previously couldn't live. Although seemingly minor, small increases in temperature and slight changes in rainfall are predicted to have major consequences in coffee growing areas. While the conditions might make high-quality coffees more abundant and cheaper for a few years, the price will eventually rise as availability sinks in the long term, researchers said.

As a result of climate change, Central America farmers might have to move their crops to higher elevations, where less land is less available.

"Farmers are going to have to try to squeeze onto that land," said Rafael A. Diaz, a Costa Rican economist who is part of a four-country research project aimed at documenting the effects of climate change on small coffee farmers.

The changes could be devastating for farmers, who will eventually be forced to replace their coffee trees with another crop to survive. Coffee, the world's second-largest traded commodity behind petroleum, supports around 25 million growers and 100 million people around the globe once family members are added.

At the Santa Anita Cooperative, farmers said they have already felt a change. Climatic evidence is supporting them. The weather center nearest their farms has recorded a .5 degree Celsius increase in temperatures and a 14 percent increase in average rainfall from the 1990s to the 2000s, according to data from the country's weather ministry.

A recent study by the Center for Tropical Agricultural Research said just a 1 degree Celsius rise in Brazil's Sao Paulo growing region, for instance, would cause a drop in coffee production worth more than $113 million.

Central America is one of the regions likely to get both hotter and drier in coming decades. In the short term, that could actually help the few farmers growing high-quality coffees at high altitudes.

"As a scientist it pains me to say it, but the conditions for coffee growing in many of the highland areas, where the best coffee is grown, could be better for coffee in the coming years," said Edwin Castellanos, a scientist for Guatemala's Universidad Del Valle, who is part of a team conducting the regional study.

Governments in the region have long urged coffee growers to move to higher elevations, where finer coffee can be grown.

"The coffee grown at those altitudes could have higher yields and it's likely that the producers will be able to take advantage in the short term by growing those high quality coffees more abundantly," he said.

However, less land is available at those altitudes. According to Anacafe, the Guatemalan coffee-growing association, only 2.5 percent of Guatemalan land is suitable for growing coffee, producing some 495 million pounds of beans. About 150 million pounds of that coffee was grown at elevations of lower than 4,500 feet above sea level, lands that are likely to be hit by climate change.

The farmers at Santa Anita, which sits about 4,000 feet above sea level, consider the changing temperatures a serious threat to their way of life. "If we have to pick all the coffee in October and November, we won't have enough help because our children will still be in school," said Mariola Cifuentes, a coffee grower in the cooperative. "And if we can't pick the coffee, it will fall [off the plant]. And we can't afford that."

Cifuentes said the increase in temperatures has led to the spread of pests and of a fungus known as koleroga. As a result, the farmers — who raise Fair Trade- and organic-certified coffee — have had to spray fungicides and pesticides more frequently.

"Dealing with these changes by spraying more fungicides or pesticides, because they are organic, is already costing these farmers more," Huerta said.

Scientists said the problem could be worse in the long-term.

Farmers could combat some of the changes in humidity and temperature by using shade trees. In some cases, the trees could be trimmed to release trapped humidity. In others, more shade trees could be planted to cut down on the sun and heat that reaches the beans, Castellanos said.

But adapting their farms to the changing climate will only last so long.

"It's a problem of increased extremes," Castellanos said. "Farmers in these regions will see hotter temperatures, longer periods of drought, more heavy downfalls, which can damage crops, and more storms."