Planting for Global Cooling
By Neva Knott
It’s Autumn, a time of change for trees. The growing season is coming to a close, though in walking around one can see some species are just now coming to fruit or seed. Leaves are beginning to turn and fall. As I watch colors move from green to gold and orange, I’m reminded of what trees do, how they function as part of the system of nature. Humans breathe out, and trees breathe in. It is the most basic symbiotic relationship. Trees breathe carbon dioxide and store—or sequester—it, keeping it out of the atmosphere. As I reflect on this changing season, I see a solution to climate change—planting trees.
The relationship between trees and global warming is much like shade and open areas on a hot day. When the sun is blazing, people and animals become too hot, and seek shade under a tree to cool. Same thing for the planet. The sun is beating down, and trees help with cool-down. The grass under the tree’s canopy remains green; the sidewalks of tree-lined streets are cool, and the homes there stay comfortable even in mid-afternoon. Stream-side trees keep water cool enough for fish to live. City trees invert the heat island effect—that sensation of bricks and concrete giving off warmth at the end of a hot day. While trees are working to cool things, they are also taking up carbon dioxide emitted by all the driving and industry of humans going about the day.
As trees grow, they accumulate carbon. Carbon sequestration occurs when the carbon taken in is stored in the wood, leaves, roots, and soil of the tree. This capacity for storage of carbon is an important focus of urban forestry programs like Friends of Trees.
As it stands now, the earth’s overall ecosystem is taxed by the amount of carbon emitted from driving and industry, using wood for fire fuel, and clearing land for development and agriculture. Oregon’s emissions measure about 68 million metric tons per year. This averages to about 17 metric tons per capita, in contrast with the world average of about four metric tons. Tree planting programs can help create carbon sequestration necessary to counteract climate change caused by excessive carbon emissions. For example, 20 mature trees store the amount of carbon emitted by driving a car 60 miles per day per year. And—an added bonus to the work of Friends of Trees—urban trees begin to store carbon at an earlier age than trees in the wilderness.
People and forests are symbiotic in nature. This symbiosis unites us—all of us—around the world, and creates universal hope for global cooling. As I look out my window, I see foliage that I know will be gone in a month, leaving my view barren and cold. Autumn, and then it’s tree-planting season—November through spring.
– Neva Knott is a Crew Leader with Friends of Trees and runs The Ecotone Exchange, a blog of positive stories of the environment.