This is the second part of a Los Angeles Times series about the problems posed by population growth. Part 1 appeared Wednesday on Page A1.

DADAAB, Kenya —

His rib cage rose and fell with tight, rapid breaths.

Saad Siyat looked shrunken beneath the hospital blanket. His wide-set eyes rolled up into his head, and his body burned with fever.

The boy was unconscious and convulsing when his aunt brought him to the hospital at Ifo camp, one of five massive camps in eastern Kenya filled with Somali refugees. The family had arrived months earlier after a nearly 300-mile journey across the desert.

Saad was suffering from pneumonia and chronic undernourishment — in particular, a protein deficiency known as kwashiorkor. The name derives from a West African term for “rejected one,” a child pushed from his mother’s breast to make way for a newborn.

Saad was 21⁄2 years old. He weighed 18 pounds.

“This child has been sick a very long time,” Dr. Ibtisam Salim said as she made her rounds in the hospital’s stabilization center, a concrete building filled with emaciated children lying on squeaky metal beds.

She felt Saad’s forehead and questioned his aunt, who was shooing away flies and using a soiled rag to wipe mucus from his oxygen and feeding tubes. The boy’s mother was at home, tending to her seven other children.

Salim gently held up one of his feet, to show the swelling, a classic symptom of protein deficiency.

“Malnutrition opens up a very big window for infection,” Salim said. “It destroys their defenses.”

She heard a gasp and stiffened.

“Excuse me,” she said, wheeling around on her heels and digging in her bag. She pulled out a stethoscope and held it to the boy’s chest.

With the tips of three fingers, she began pumping rapidly on his frail torso.

Where life is precarious

Around the world, population is increasing most rapidly in places where life is most precarious.

Across Africa and in parts of South Asia and Latin America, hundreds of millions of people live on the edge of starvation. A drought, flood or outbreak of violence can push them over the brink.

Many end up on the march, crossing borders in search of relief. Some arrive in places like Dadaab, famished and desperately ill. Millions more are displaced within their own countries.

They represent one face of hunger in a world that, on paper at least, produces enough food to feed all 7 billion inhabitants.

Somalia, a nation of 10 million, has one of the highest birthrates in the world, averaging 6.4 children per woman. Runaway population growth, food scarcity and political strife have combined to cause a mass exodus. One-fourth of Somalis have fled their homes.

Last year, during the worst of a three-year drought, shortage turned to famine. Forty percent of Somali children who reached the refugee camps in Dadaab were malnourished. Despite emergency feeding and medical treatment, many died within 24 hours.

More commonly, children live on tenuously, the effects of chronic malnutrition masked by the swelling caused by kwashiorkor. By the time their parents realize how sick they are and take them to the camp hospital, it can be too late.

An ephemeral revolution

It has been four decades since advances in agriculture known as the Green Revolution seemed to promise relief from this kind of mass suffering.

An American plant breeder named Norman Borlaug won the Nobel Peace Prize in 1970 for helping to develop high-yield, disease-resistant varieties of wheat and other grains, making it possible to triple harvests around the world.

Mankind finally seemed to be gaining ground on its longtime nemesis: pervasive hunger.

Yet Borlaug cautioned against hubris: “The frightening power of human reproduction must also be curbed,” he said. “Otherwise, the success of the Green Revolution will be ephemeral only.”

Today, with nearly twice as many people on the planet, his words seem sadly prescient.

Nearly 1 billion people are malnourished, according to the U.N. Food and Agriculture Organization. At least 8 million die every year of hunger-related diarrhea, pneumonia and other illnesses — more than succumb to AIDS, malaria and tuberculosis combined. A child dies of hunger every 11 seconds.

Enough for all — on paper

In raw volume, the world’s farmers produce enough food for everyone. People go hungry in developing countries because they can’t afford to buy food and can’t grow enough on their own. Inadequate transportation and storage aggravate shortages.

By midcentury, global food production could simply be insufficient. There will be at least 2 billion more mouths to feed, and an expanding middle class will consume more grain-fed beef, pork and other meats.

To meet the demand, the world’s farmers will have to double their crop production by 2050, according to researchers’ calculations.

Jonathan Foley, a University of Minnesota climatologist, says it’s the challenge of the 21st century: “How will we feed 9 billion people without destroying the planet?”

Most of Earth’s best farmland is already under cultivation, and prime acreage is being lost every year to expanding cities and deserts, contamination from agricultural chemicals and other causes.

Carving large new tracts of farmland out of the world’s remaining forests and grasslands would exact a heavy toll, destroying wildlife and unleashing climate-warming gases now locked in soils and vegetation.

Complicating the problem is that rivers and aquifers are running dry, and heat waves and droughts associated with global warming are withering crops. Pests and diseases thought to have been vanquished are bedeviling farmers again, often in more virulent forms.

No solutions in sight

Major international research projects are under way to develop hybrid crops to withstand these challenges. But such efforts take decades, and there is no guarantee of success.

“The easy things have been done,” said Nina V. Fedoroff, a biotechnology expert at Pennsylvania State University. “The problems that are left are hard.”

The traditional low-tech solution to hunger — mass migration — is increasingly impractical on a crowded planet.

The looming crisis is expected to be most severe in Africa, where birthrates are high and where the Green Revolution never took hold. By midcentury, the continent’s population is expected to double — to 2 billion.

Africa already is home to nearly 30 percent of the planet’s chronically hungry. About 400 million people in sub-Saharan Africa live on less than $1.25 a day, most of which is spent on food.

Increasingly, they are competing with the appetites of wealthier nations, which are snapping up some of Africa’s best rain-fed farmland to secure long-term food supplies. The U.S., China and other countries are also using more grain to fatten livestock and make ethanol, pushing up prices.

All of this leaves more and more people on the edge.