 This may have knock-on effects on other parts of ecosystems as herbivores will need to eat more food to gain the same amount of protein.Studies have shown that higher CO2 levels lead to reduced plant uptake of nitrogen (and a smaller number showing the same for trace elements such as zinc) resulting in crops with lower nutritional value.This would primarily impact on populations in poorer countries less able to compensate by eating more food, more varied diets, or possibly taking supplements.