Which of the following could limit the potential for increased crop yields in a changing world?Plants growing smaller leaves as a result of increasing emissionsThe spread of crop pests and diseaseMore atmospheric CO₂

All of the options mentioned could potentially limit the potential for increased crop yields in a changing world. Here's why:

1. Plants growing smaller leaves as a result of increasing emissions: If plants grow smaller leaves due to increased emissions, they may not be able to photosynthesize as efficiently. Photosynthesis is the process by which plants convert sunlight into energy, and leaves are the primary site of photosynthesis in most plants. If leaves are smaller, they have less surface area to capture sunlight, which could limit the plant's growth and productivity.

2. The spread of crop pests and disease: Pests and diseases can significantly reduce crop yields by damaging or killing the plants. As the climate changes, pests and diseases that were once limited to certain areas may be able to spread to new areas. This could expose crops to new threats that they are not equipped to handle.

3. More atmospheric CO₂: While plants need CO₂ for photosynthesis, too much CO₂ can actually be harmful. High levels of CO₂ can cause plants to grow more quickly, but these plants often have lower nutritional value. Additionally, some studies suggest that high levels of CO₂ can make plants more susceptible to pests and diseases.

So, all of these factors could potentially limit the potential for increased crop yields in a changing world.