Why Arbor Day is so Important Today is one of the most important environmental holidays: Arbor Day. Everybody should be informed about the importance of this holiday and why trees are necessary to sustain life on Earth. For you: We Need Trees What is Arbor Day? Arbor Day is a holiday when people are encouraged to plant trees. It's observed on the last Friday of April and has been celebrated since the 1870s . Millions of trees have been planted on Arbor Days. Why it's Important Global warming is caused when too much carbon dioxide enters the atmosphere. That causes our planet to heat. Humans and human activity increase the amount of carbon dioxide in the air. How do we combat this? Trees. Not only do trees absorb carbon dioxide; they also create oxygen which humans and animals need to breathe. Also, trees provide us with food and boost the economy . How to celebrate Planting trees is the greatest way to celebrate Arbor Day. Every tree planted has monumental impacts on our plane...