Policymakers on Capitol Hill got a dire warning that climate change threatens food production, safety and affordability.

That stark message came in a briefing by the American Meteorological Society to congressional staff members, climate scientists and federal regulators that linked climate change to a host of troubling scenarios involving worldwide food availability.

Wednesday's briefing drew on a peer-reviewed study by the U.S. Department of Agriculture released during the Paris Climate Conference last month. That report, "Climate Change, Global Food Security and the U.S. Food System , " concluded that the effects of climate change on food will strike urban and rural populations in wealthy and poor nations alike.

While the threat depends on many factors, its impact will increase by mid-century, according to the report. Under the least-optimistic scenario––based on high carbon emissions and low international cooperation to combat climate change––agricultural yields could fall by as much as 15 percent, and food prices could rise more than 30 percent by 2050.

"Climate change puts the world's food security at risk through both direct and indirect factors," said Margaret Walsh, an ecologist in USDA's Climate Change Program Office and one of the authors the report.

Widespread drought caused by climate change could decrease crop production, Walsh told InsideClimate News. At the same time, sea level rise could impact cargo ships' access to docks for importing and exporting food.

"There are many, complex factors that have to be considered when assessing the threat to food security," Walsh said.

Global Warming, Global Warning

Global food security––defined as people having access to safe and nutritious food sufficient to lead healthy lives––has improved over the last six years, with 200 million fewer people at risk, Walsh said. (The USDA estimates that 805 million people worldwide do not have sufficient food today.) Yet predictions of increasing global temperatures could signal a halt in the progress toward curbing global hunger.

Risks to food security will increase as the magnitude and rate of climate change increases. Even moderate changes in global warming are predicted to have a detrimental effect on global food sources, Walsh said.

USDA scientists calculated the consequences associated with worst- and best-case scenarios, based on the current level of greenhouse gases, which is around 400 parts per million.

A worst-case projection based on high greenhouse gas concentrations in the 850 ppm range, coupled with high population growth and low economic growth, concluded that 175 million more people will be at risk of undernourishment by 2080. The same socioeconomic conditions at 550 ppm would result in 60 million additional people at risk, and if concentrations drop to 350 ppm, risk does not increase at all.

Climate is the most important influence on agriculture, Walsh said. Crops are adapted to particular patterns of temperature, rainfall and the length of the growing season. When climate changes those parameters, agricultural systems are disrupted.

'Who Gets to Eat?'

Ed Carr, a professor of international development, community and environment at Clark University in Worcester, Mass., used wheat production in northwestern Europe and rice production in eastern Asia to illustrate that tenuous balance. Together, those two regions produce one-third of the world's grain crops.

The wheat and rice output has been pushed to the limits that the soil can support and the grain variety can produce, said Carr, who was one of the speakers at the briefing.

"You add climate change to that mix and you are taking a stressed system and stressing it even more," he said.

Rising temperatures mean the grains won't germinate; rain patterns are disrupted so crops are stunted and growing seasons are altered, Carr said.

"We are already in a world where we are bumping up against the limit of what we can produce so any additional stress factors can have significant consequences," he said.

Less production means price increases and a shifting of markets, Carr said. The food will go to the markets that can afford the higher prices, leaving poorer nations wanting.

"What we see are the consequences of climate change radiating," he said.

Other factors that must be considered, according to the researchers, is that climate change also disrupts transportation, storage, packaging and delivering food–– making it harder for people to get enough of the right kind of food, especially in regions already facing shortages.

One of the least recognized factors is how social and cultural norms in various communities and even households will shape food distribution and preferences during shortages, Carr said.

"If there is inadequate food available to households––who gets to eat?" Carr said. "In parts of Africa, boy children will be fed preferentially over girl children.

"So basically we don't know a whole lot about the social and cultural norms that are critical to food access, so most of our measures of food access are related to food price, which is a very partial measure of access at best."

Although the United States may be vulnerable to climate change-related disruptions in productivity, it appears likely to endure with fewer hardships than the rest of the world, USDA researchers said.