Global food prices are expected to rise in the long term as population grows, but a new study warns that severe weather events like this year's drought in the U.S. could spike prices higher suddenly. - 

The U.N. said this morning that global food prices were flat in August, easing fears of a global food crisis for now. But the future of those prices isn’t set in stone.

"That’s one of those questions, if I knew the answer to, I’d be a rich man," said David Lobell, a professor at Stanford.

Still, you can probably make a pretty good guess. "Most assessments put future prices at significantly higher than they have been in the last decade or two," he said.

More people, hungrier for more food, are part of the reason.

There are also supply issues -- among them climate change. A new study from OxFam says climate change will cause a steady increase in price among staple foods, but it could also cause dramatic spikes -- prices doubling in days -- as droughts and floods become more regular.

"The research that we did tells us that climate change is going to drive increasing weather shocks, and that those weather shocks are going to cause more dramatic price spikes in global food prices," said Heather Coleman, who's with OxFam.

And, she said quick changes in food prices are much harder for people to handle, especially in places where getting enough to eat accounts for most of a family’s budget.

Follow Adriene Hill at @adrienehill