 Plants need four key things to grow. Light, water, carbon dioxide, and fertilizer. Anyone who has a farm, a garden, or a house plant knows that plants need the right balance of all these things. No amount of fertilizer will help a plant that has no water. Scientists studying the impacts of climate change on agriculture look at all aspects of the system. Of those four factors, light will change the least. But water is a big concern. Changing the climate changes where and when rain falls. Some areas become more wet, and other areas become more dry. Rain might come too early or too late for crops. Hotter air holds more water, so when it rains, it pours. Floods wash away seeds and plants. Climate change can cause problems for fertilizer because heavy rain washes it out of the fields and down rivers. A common myth ignores that fact and claims that CO2 is a plant food. This is an oversimplification. It chooses a single piece of a complicated problem and ignores the other parts. It's like saying humans need calcium, so all you need to live on is ice cream. Carbon dioxide makes plants grow faster when they're in an ideal environment, like inside a greenhouse where they have the right amount of water and fertilizer. But for the basic needs of plants, we need to consider carbon dioxide and water. It's not enough to have the basic necessities of life. Plants also have to be safe from danger. One big danger for plants is hot temperatures. Our major agricultural crops have ideal temperature ranges. As the temperature goes up, crop yields go down. Plants are especially sensitive to extremely hot days. Some other creatures love hot weather. Unfortunately, many of them are pests, like the Colorado potato beetle, the European grapevine moth, and a nasty wheat blight called FHB, or Fusarium head blight. Some pests, like FHB, even prefer the taste of crops that have grown with more CO2, and they grow faster. Many pests are migrating north as the climate warms into areas where they've never been seen before. The overwhelming consensus among agricultural scientists is that the negative impacts of climate change on crops far outweigh the small benefits that plants gain from extra CO2.