The presence of carbon dioxide in the atmosphere has contributed to the greenhouse effect. Whether this is caused by the actions of humans or is part of a natural cycle is a much debated matter. Nevertheless, all trees contribute to the production of oxygen, which is a very good thing for creatures that breathe it, like humans. Generally speaking, larger trees produce more oxygen than smaller trees. Trees also absorb and lock away carbon dioxide, according to The Arbor Day Foundation and many other bodies.
Trees provide oxygen and shade for humans and homes for small mammals, birds and insects. They look good; a wood or forest of trees is great for walking, running and cycling through. Trees provide humans with lumber for buildings, furniture and other manufacturing. The horse might be man's best friend, but the tree is a strong contender for being man's best plant friend. But whether it can save the planet is a matter of opinion.
According to a Gallup Poll, most Americans think global warming is largely because of natural causes. The rest of the world tends to disagree with Americans, but perhaps Americans are better informed than the rest of the world. If the majority of Americans are right, then perhaps no trees can stop global warming. You could demolish every human structure on the planet and plant every bit of land with trees and it might not make any difference to global warming whatsoever.
If the majority of Americans are wrong, perhaps we need to plant trees by the millions. Indeed, this is the plan of Million Trees NYC. This is an ambitious, part public, part private program to plant a million of man's best plant friend across the City's five boroughs in the next 10 years. Three-fifths of those trees, approximately 600,000, are to be planted in parks, as well as other public areas. Two-fifths, approximately 400,000, will be planted on private land.