At a recent lunch, a woman asked about carbon sequestration, since she was concerned about the amount of carbon humans are responsible for pumping into the atmosphere with their automobiles, air travel, electrical consumption and other uses.

Increasing amounts of carbon dioxide in the air have been linked to global climate change. Carbon sequestration is the process of using nature or technology to suck carbon dioxide back out of the atmosphere and lock it up somehow.

One suggestion has been planting great forests, with trees that will inhale carbon dioxide from the air and store it as wood. After a little research, I concluded it would take a lot of trees.

The U.S. Energy Information Service figures that the average annual U.S. production of carbon dioxide per person is about 20 metric tons — roughly 44,000 pounds. The average African uses a fraction of that, and because we don't have as far to drive and don't heat our homes in winter, Hawai'i folks use may be a little less than the U.S. average.

You can work out your own rough production, your "carbon footprint," at sites like www.greenprogress.com/carbon_footprint_calculator.php and www.carbonfootprint.com/calculator.html. There are lots of these calculators on the Net. Try several, since they do the calculations in different ways, and can produce different results.

Let's say you planned to plant enough trees to remove as much carbon dioxide from the atmosphere as you produce.

The U.S. Environmental Protection Agency says that a southern pine plantation sequesters one metric ton per acre per year. Let's say you're frugal with your production and are responsible for half the national average — just 10 metric tons annually. You'd need to plant 10 acres of pine trees.

Another source, colorado trees.org, suggests 2.6 tons of carbon dioxide sequestration per acre per year is possible. With these trees, only five acres would more than do the trick.

Never mind whether you could afford to buy or lease five acres of Hawai'i land. Here's the problem.

There are about 1.2 million people in Hawai'i, and about 4.1 million acres of land — much of which is already forested, some of which is producing food, some is in urban use and so on.

If you forested everything possible, and assumed it all sucked up maximum amounts of carbon dioxide, there is not enough space in Hawai'i to sequester the current carbon dioxide production of Hawai'i's residents.

If you have a question or concern about the Hawaiian environment, drop a note to Jan TenBruggencate at P.O. Box 524, Lihu'e, HI 96766 or jant@honoluluadvertiser.com. Or call him at (808) 245-3074.