What About Global Warming?
By Jan Scow
One of the most pressing issues in the news these days is global warming. It is an important issue, and trees play a role in it, but it may not always be clear exactly what that role is. I offer a simple discussion below for those who are interested in understanding more about the subject.
Global warming is probably a natural occurrence to some extent, and some people would have us believe it is nothing more than that. Most scientists, however, think that we are contributing to global warming through our activities, and that we are accelerating the rate at which global warming occurs. The “greenhouse effect” is widely believed to be a major factor in global warming. So-called greenhouse gases such as water vapor, carbon dioxide, and methane allow sunlight to pass through them and warm the earth. As the earth’s surface warms, energy is radiated back into space in the form of heat. Because this radiant heat has a longer wavelength, some heat is absorbed by greenhouse gases in the atmosphere and reradiated back toward the earth causing additional warming of the earth’s surface. As the concentration of greenhouse gases in the atmosphere increases, the warming effect increases.
One greenhouse gas that is increasing in the atmosphere is carbon dioxide (CO2). Internal combustion engines used in most cars produce CO2, and contribute significantly to the gain of this greenhouse gas. But there are also many other sources: Aircraft engines, coal-burning electricity-generating plants, home fireplaces, small engines, and forest fires also contribute to the release of CO2 into the atmosphere. All of these processes burn carbon-based materials (gasoline, jet fuel, coal, wood) in oxygen and release energy, along with CO2 and various other byproducts. Other sources of greenhouse gases include thawing tundra (frozen tundra decays when it warms and thaws, releasing CO2), livestock farming (methane, CO2), and vented landfill emissions (methane, CO2).
The carbon that is released in the burning of fossil fuels, wood, and wood products is the same carbon that can be “sequestered” by the growing of trees and plants. When a plant grows, it combines CO2 with water, using solar energy (photosynthesis), creating complex hydrocarbons (glucose, wood, etc.), and releasing oxygen into the atmosphere. So, in effect, sequestration is the capture and storage of carbon atoms in the production of living tissues.
When trees die and fall to the ground, they usually decay within a few years to decades, releasing CO2 slowly back into the atmosphere. By contrast, when a forest fire occurs, or when forested land is cleared and burned for agriculture, huge quantities of CO2 are released into the atmosphere very quickly. Removing a single tree and turning it into firewood will have a similar rapid conversion, although on a much smaller scale. Under the right conditions, trees in a forest or jungle may become buried or submerged and eventually converted into crude oil and/or coal. That process takes millions of years, but that is where the carbon in our fossil fuels came from.
Trees are one of the best carbon sequestration vehicles, since they are large and long lived, and they decay slowly when they die. The more trees that are growing on the planet, the less free carbon there is likely to be in the atmosphere. Think about that when you consider removing a tree. I do!
Jan is a Registered Consulting Arborist and a Board Certified Master Arborist on the Ojai Trees Board of Directors.