Small increases in temperature may have reduced the industrial and agricultural production of poor countries, according to a study by U.S. economists. Higher temperatures may also have contributed to political instability in these countries — defined as those with below-median per capita income, adjusted for the purchasing power of the country’s currency — according to the study published in the American Economic Journal: Macroeconomics. In contrast, rich countries have so far shown no measurable economic or political consequences resulting from temperature change.