About 870 million people around the world are undernourished, meaning one in eight humans doesn't get enough food to be considered healthy. But according to a new report from charity group Oxfam, climate change could raise that number by another 20 percent, part of a "vicious spiral" of falling incomes, rising prices and declining food quality.

This warning comes ahead of the latest synopsis by the Intergovernmental Panel on Climate Change, a U.N. agency whose last major report came out in 2007. The IPCC outlines an array of risks posed by climate change, and its new overview concludes with 95 percent certainty that people are fueling the problem — up from 90 percent six years ago.

"Just as the evidence of manmade climate change is becoming stronger, so too is our understanding of how it hits people, especially around hunger," says Tim Gore, head of policy for Oxfam's GROW campaign, in a statement about the report. "We've long known that climate change will mean lost crops, but increasingly we're seeing its impacts through higher food prices, lower earnings, more health problems and lower quality food, too."

The IPCC is the world's top authority on climate change, producing periodic research summaries that cover a multitude of ways warming affects people. Oxfam's report focuses on food availability, yet still brims with dangers to human life and health. Not only can climate change doom entire harvests with floods, droughts, heat waves and cold snaps, Oxfam warns, but it poses a sweeping threat unseen in 10,000 years of human farming.

"The changing climate is already jeopardizing gains in the fight against hunger, and it looks set to worsen," the report says. "If the remainder of the 21st century unfolds like its first decade, we will soon experience climate extremes well outside the boundaries of human experience, ever since agriculture was first developed."

Australia drought

A farmer kicks up dust from his dry barley fields in Perkes, Australia. (Photo: Ian Waldie/Getty Images)

Although climates change naturally over time, the current greenhouse effect's speed and scope are unprecedented in human history. And with Earth's human population now more than 7 billion, the planet's ability to produce enough food is already stretched thin.

The number of people at risk of hunger may rise by 10 to 20 percent before midcentury, according to Oxfam, with disproportionate effects for low-income people in developing countries. But while poorer communities are less buffered, climate change is still a global problem. Disasters like the 2010 Pakistan floods or the 2011 Horn of Africa drought are increasingly matched in wealthier nations by events like the 2011 floods in northeast Australia or the 2012 droughts in Russia and the U.S. Midwest. Daily per-capita calorie availability will likely fall worldwide in coming decades, Oxfam warns.

Smaller harvests typically lead to higher prices, often compounding other economic woes festering in the wake of meteorological disasters. Last year's droughts in the U.S. and Russia, for example, cut their respective countries' corn and wheat harvests by 25 percent each, resulting in steep price increases at home and abroad. According to the U.K. Institute of Development Studies, which Oxfam commissioned to research future prices, "the average price of staple foods could more than double in the next 20 years compared with 2010 trend prices — with up to half of the increase caused by climate change."

Higher average temperatures help some crops mature faster, but without the right balance of water and nutrients, that growth may go into their stems instead of the grain or fruit. More warmth can also favor crop pests, Oxfam notes, including fungi that contaminate plants with dangerous mycotoxins. And while extra carbon dioxide boosts the growth of certain crops, it also reduces protein concentration in wheat, barley, rice and potatoes.

Even without crop failures or lower food quality, Oxfam says its work in climate-related emergencies shows that compromised infrastructure can be at least as big of a problem. "[T]he effects on transport, storage, bridges, fuel supplies and other vital food-related infrastructure can in some instances be a bigger constraint on availability, and a bigger driver of food price increases, than impacts on food production," the report warns.

Earth's food system has proved adaptable in the past, and Oxfam strikes an optimistic tone despite its dismal forecasts. "The climate change impacts on food security set out in this brief are not inevitable," the report concludes. "But a dramatic shift in political ambition and a significant scale-up in resources are urgently needed to avoid dangerous climate change, address our broken food system, and strengthen its resilience."

Citing this week's IPCC report, Gore says the specter of expanding world hunger can help put a face on the seemingly abstract threat of climate change — and help spur diplomats and policymakers to do something about it. "We want a world in which everyone enjoys the right to enough affordable and nutritious food, and we cannot allow climate change to throw us off course," Gore says. "Leaders listening to the latest findings from climate scientists this week must remember that a hot world is a hungry world."

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Russell McLendon ( @russmclendon ) writes about humans and other wildlife.

A hotter world is also hungrier, report warns
From damaged crops to disrupted economies, climate change threatens food availability for a growing swath of humanity, according to charity group Oxfam.