As leaders from more than 130 nations convene a United Nations conference on sustainable development Wednesday, new research shows how climate change will likely exacerbate a key issue: hunger.

The number of undernourished women and young children could increase 20% and affect one of every five within a decade because of climate change's impact on food production, according to an analysis by the World Health Organization and other groups. Today, one in seven or 495 million women and children under age 5 lack sufficient food, the report says, adding population growth will worsen the problem.

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Food security is a top issue -- along with poverty, energy shortages and rain forest destruction -- at this week's U.N. Conference on Sustainable Development in Rio de Janeiro, Brazil, also known as Rio+20 to mark the 20th anniversary of the initial Earth Summit. Delegates will try to negotiate commitments for spurring economic growth without harming the environment.

The WHO analysis shows that of the 495 million women and children under age 5 who are undernourished, 150 million live in Africa, 315 million in Asia and 30 million in Latin America and the Caribbean. It expects about 465 million more will live in developing countries by 2020, boosting food demand.

"Undernutrition is a determinant of poor health and it is women and children who suffer the most," Julio Frenk, dean of Harvard University's School of Public Health, said in announcing the findings. "Maternal undernutrition can continue in children, extending the cycle for at least three generations."

The report says climate change will also affect food prices. Citing World Bank data, it says those prices jumped 8% in the first quarter of 2012, partly due to extreme cold in Europe that affected wheat crops and excessive heat in South America that lower production of sugar, maize and soybeans.

Another report, published today in the journal Energy and Environmental Science, suggests several solutions to climate change and food shortages: farm efficiency, food waste recycling and lower meat consumption.

These changes could reduce the amount of land needed for farming, despite population growth, and leave sufficient land to produce bio-energy, according to the study from the University of Exeter in the United Kingdom.

At Rio+20, diplomats are negotiating an 80-page document on the meeting's goals, although they're not expected to approve financial or other aid for the developing world. Secretary of State Hillary Rodham Clinton is representing the U.S., because President Obama is not attending.

The corporate world is also active at the U.N. conference. Two dozen major companies made new environmental commitments earlier this week. Coca-Cola, for example, pledged to develop plans to protect the water sources for its 200 bottling plants worldwide.