Oxfam, the international nonprofit, issued a report on Tuesday estimating how extreme weather events might affect food prices in the coming decades — forecasting that the prices of a number of food staples could surge far beyond the projected increases. “We will all feel the impact as prices spike but the poorest people will be hit hardest because they often spend up to 75 percent of their income on food,” said Heather Coleman, climate change policy adviser for Oxfam America, in a statement.