They show that in the medium term - that is, until about 2030 -the positive and negative effects on yields could offset each other at the global level, the balance after this date would be increasingly negative as climate change accelerates. The data also show that projected impacts of climate change on yields of maize, wheat and rice in the second half of the 21st century are more often negative for tropical regions than for temperate regions. However, in many locations in temperate regions, as well, crop yields may decrease (Porter et al.,