Mexico and Central America could lose around a third of land suitable to grow coffee as global warming hurts conditions for the best quality beans, a study of regional farms shows.

Specialty arabica coffee, the pride of countries like Guatemala, grows inside a very narrow band of altitude and temperature making it particularly sensitive to small changes in the climate.

At the current rate temperatures are rising, there could be at least a 30 percent net loss in land suitable to farm coffee in Mexico and Central America by 2050 forcing many farmers to turn to different crops, said Peter Laderach, a lead researcher at the International Center for Tropical Agriculture.

Laderach, whose organization is based in Colombia, is leading a team of scientists who started studying 7,000 small farms in Guatemala, Mexico, El Salvador and Nicaragua in 2009 and has based his estimate on data collected so far.

The researchers map the farms with satellite positioning devices to collect data on altitude and crop production. That information is then cross-referenced with climate change models to track how different areas will be affected by hotter weather and changes in rainfall.

In San Lucas Toliman, a village nestled between two volcanoes in western Guatemala, 140 farmers from the Granja Juan Ana cooperative submitted mapping data to the project.

"We want to know what will happen to be more aware. We hope to pass the information to everyone so we can be prepared," grower Julio Morales said, whose family has farmed coffee in the area for more than two decades.

Greenhouse gas emissions could heat the earth's surface by between 2 and 11 degrees Fahrenheit (1-6 degrees Celsius) over the next 100 years, according to the United Nations, forcing farmers of all kinds of crops to change habits.

TRYING TO ADAPT

Unpredictable rainfall patterns, excessive droughts, and hurricanes caused by climate change are already affecting coffee farmers from Kenya to Vietnam. Mexico and Guatemala are among the world's top ten coffee producers by volume, according to the International Coffee Organization and shrinking coffee land will eventually affect the global market.

"We'll have much less coffee available and for those who can still produce, the price could go up," Laderach said.

Laderach's research has shown the changing weather will mean growers farming coffee at low altitudes will lose crops.

Higher altitudes, which now are too cold to grow coffee, will become farmland but higher up, land is scarce. Poor farmers in Central America, where most of the property is concentrated in the hands of a small number of owners, have trouble acquiring new land.

Many farmers between the low and high extremes will need to adapt their farming methods to continue producing coffee.

The scientists are using the data to give farmers advice on how to change practices. Some can plant shade trees to lower the temperatures over their trees, others can change to drought resistant varieties of coffee or install irrigation systems.

"If there's a whole portion of the coffee supply chain that 20 or 30 years from now can't grow as much, can't grow the same quality or perhaps can't grow coffee ... (we) want to know that now," said Michael Dupee, vice president of the U.S.-based Green Mountain Coffee Roasters Inc (GMCR.O) helping to fund the research. (Writing by Mica Rosenberg; Editing by Marguerita Choy)