Lake San Antonio, California. Daniel Griffin World population continues to grow, and an exploding middle class in emerging countries, especially China, is going to drastically change our food supply and farming practices, according to the latest Grantham Mayo van Otterloo quarterly report.

The biggest problem is that the growing middle class is consuming more meat than ever before, according to the report.

Global water supply is already stressed, and raising cattle and washing and processing the meat requires more water than most crops.

More meat consumption is a huge drain on resources, but it's not the only problem.

The growing middle class and worldwide population growth is also straining soy and grain reserves. Prices of wheat, corn, soybeans, and rice are already twice what they were in 2000, the report says, and prices are expected to double again in the next couple decades.

Lloyd's 2015 Emerging Risks Report warns of even more devastating effects on grains in the next few decades:

Lloyd's Emerging Risk Report

More middle-class families will also put much more pressure on farmers, according to research from the World Institute of Development Economic Research. Right now there are about four rural dwellers for every city dweller in Asia and Africa, but according to UN projections, by 2040 that ratio will only be 2:1. That means growers will need to feed twice as many city inhabitants by 2040.

The biggest change will happen in China. Right now more than 40% of Chinese citizens live in rural areas, but in the next five years the country plans to move 100 million of those people into cities. By 2026, it wants to move 250 million.

But to provide for those cities, the rural population will need farming innovations and a big surge in productivity with fewer people working the land. This same shift is happening in other emerging countries with growing middle classes.

That's bad news since the UN estimates we'll have to double agricultural output by 2050 to keep up with worldwide population growth. But simply ramping up farming output may not be a viable solution. Climate-change fueled droughts and floods are already creating difficult farming conditions in many places, especially in Africa, Asia, and Latin America. Floods in particular speed up soil erosion — which is already happening about 100 times faster than the rate at which soil can naturally recover, according to the Grantham report.

The destructive weather events will affect some areas more than others, according to the Lloyd report:

Lloyd's Emerging Risks Report

The bottom line is that if the world continues with business as usual then it could lead to a global food crisis, according to a report from the Global Sustainability Institute.

"The results show that based on plausible climate trends and a total failure to change course, the global food supply system would face catastrophic losses and an unprecedented epidemic of food riots," the Global Sustainability Institute's report concludes. "In this scenario, global society essentially collapses as food production falls permanently short of consumption."

The good news is that we can stop this from happening, but we'll need more sustainable farming practices or a global diet change to do it.

The Food and Argricultural Organization estimates that about 30% of the food produced in North America and Europe gets thrown out, so eliminating that waste could go a long way to feeding the growing population.