The effects of climate change on food production could cause 500,000 extra deaths by 2050 compared to a world without global warming, according to a study released Thursday.

If greenhouse gas emissions continue at current rates, this would cut projected increases in food availability by about a third before mid-century, the study found.

As of 2015, some 800 million people in the world are undernourished, meaning they cannot meet daily minimum dietary energy requirements, the UN's Food and Agriculture Organization has said.

With the global population set to increase from seven to nine billion by 2050, food production will have to expand even more rapidly if all the world's people are to have enough to eat.

But global warming -- on track to boost temperatures three degrees Celsius (5.4 degrees Fahrenheit) by 2100, compared to pre-Industrial-Era levels -- is threatening to make that difficult or impossible, experts warn.

"Climate change effects are expected to reduce the quantity of food harvested, which could lead to higher food prices and reduced consumption," according the study, published in the medical journal The Lancet.

Even these grim projections may be overly optimistic, it warns, because they only count calories and fail to anticipate a likely worsening in the balance of future diets.

"Our results show that even modest reductions in the availability of food could lead to changes in the energy content and composition of diets," said Marco Springmann, a researcher at the Oxford Martin Programme on the Future of Food at the University of Oxford, and leader of the study.

"These changes will have major consequences for health."

The proportion of fruits and vegetables in diets, for example, will almost certainly decline in a climate-change-addled world, he said.

Low- and middle-income countries will probably be hit hardest, with almost three-quarters of all climate-related deaths expected to occur in China and India under a so-called "business and usual" climate scenario.

Even if the world's nations succeed in holding the rise in global temperature to 2C (3.6F), there would still be an additional 150,000 climate-related deaths due to changes in diet and calorie intake, the researchers found.

"Climate change is likely to have a substantial negative impact on future mortality, even under optimistic scenarios," Springmann said.

The study used agricultural economic models coupled with different projections for greenhouse gas emissions and development forecasts to evaluate the impacts on global food production, trade and consumption in 2050.

Experts evaluating the research said it was worthwhile, but cautioned that such projections are uncertain.

"It is very difficult to estimate exactly what climate change impacts will be," commented Andrew Challinor, a professor at the University of Leeds in England.

"Year-to-year variability of food production will become greater, which will make global food markets more unpredictable."

Extreme climate events -- such as the wheat harvest failure in Russia in 2010 -- will also become more common, he added.