How will the increase in carbon-dioxide levels in the atmosphere (connected with global warming) affect plants? If more trees are planted, would this have any effect on atmospheric levels?

There used to be more trees (in 500yrs it is estimated we have lost 4 billion acres of trees) and less carbon-dioxide, therefore there must already be plenty of carbon-dioxide in the atmosphere for plants to use.

Increasing the number of trees is the only really proven way to reduced atmospheric carbon. Ice core samples haven shown that during the 13th century atmospheric carbon dioxide dropped. It happens to be during the Mongol conquest. The reason being that Genghis Khan wiped out entire towns and villages at a large rate (it is estimated he killed 17% of the entire human population at the time) and nature was able to take over again and reforestation occurred.

Increased carbon dioxide levels in the atmosphere due to global warming can have both positive and negative effects on plants. On one hand, higher CO2 concentrations can stimulate photosynthesis and increase plant growth rates. However, prolonged exposure to elevated CO2 levels can also lead to decreased nutrient content in plants and altered ecosystem dynamics. As for planting more trees, it can help mitigate the rise in atmospheric CO2 levels by absorbing and storing carbon through the process of photosynthesis. However, the effectiveness of this mitigation strategy depends on various factors such as the type of trees planted, their location, and management practices. Additionally, other factors such as deforestation, land-use changes, and climate change impacts can also influence the overall effectiveness of tree planting efforts in reducing atmospheric CO2 levels.