WASHINGTON — Climate change that strengthens the El Nino weather patterns could endanger food supplies for more than 20 million people in Africa, a new study warns.

El Nino is a warming of the water in the tropical Pacific Ocean that is associated with changes in air pressure and the movement of high-level winds that can affect weather worldwide.

In the past, El Ninos have occurred every four to seven years, but many climate experts worry that continuing global warming will lead to stronger and more frequent events.

A new analysis of 40 years of African crop and livestock records shows a close association between El Ninos and variations in production of corn, sorghum, millet and groundnuts such as peanuts.

Corn was particularly affected, with yield reduced in El Nino years in several African countries, researchers led by Hans R. Herren of the Millennium Institute in Arlington, Va., report in Tuesday's issue of Proceedings of the National Academy of Sciences.

In southern Africa, crop production could be down by as much as 20 percent to 50 percent in strong El Nino years, the researchers found.

There were smaller crop reductions in west Africa, they reported, but in northwest Africa there was an increase in sorghum and groundnut production in El Nino years.

Production of cassava and wheat did not vary in response to El Nino, they reported.

For Africa overall, the variation in corn production corresponded to the amount of food needed to feed 20 million people in a year, the report concluded. Variations in rice, sorghum, millet and groundnuts amounted to food for 2 million to 3 million people.

The danger could be reduced by increasing irrigation and by changing land use, including planting alternative crops, the researchers said.

The research was funded by the University of Oslo, Norway; the World Bank and the Norwegian Agency for Development Cooperation.

Source: Associated Press