Cut Global Warming? Not In My Backyard.

March marks 50 years of nearly uninterrupted measurements of the rising carbon dioxide levels in the atmosphere from Hawaii's Mauna Loa.

When the Mauna Loa measurements began in March 1958, the atmosphere already contained about 315 parts per million CO₂. It has since risen to 383 parts per million. That's a nearly 22 percent increase, driven by the burning of fossil fuels.

When displayed in graph form, the Mauna Loa record steadily curves upward from 1958 to the present. Within that curve, though, there are plenty of squiggles.

Those regular squiggles represent the dip in CO₂ levels that coincides with the greening of the northern hemisphere each spring and summer.

There is more land, and as a consequence, more vegetation, in the northern hemisphere. So when things are green north of the equator, there is a slight drawdown in the amount of CO₂ in the atmosphere. After things turn brown again in the northern fall and winter, CO₂ levels again pick up their upward climb.

On one hand, the squiggles remind us that vegetation, through photosynthesis, each year scrubs the atmosphere of at least some of its surfeit of CO₂.

On the other hand, the overall curve shows we still have the upper hand. Simply put, humans are pumping CO₂ into the atmosphere much, much faster than nature's greenery (and the oceans) can take it out.

Take the United States, where forests absorb the equivalent of just 14 percent of the nation's CO₂ emissions. That means those trees offset just one-seventh of the country's overall carbon dioxide emissions. So my question is this: Could more trees make a difference?

Not in my backyard.

Don't get me wrong, I'm all for trees — and for more trees. But if I look at how much CO₂ I put into the atmosphere by driving, doing laundry, cruising the internet, cooking and reading by the light of my bedside lamp, there’s no way I could offset those emissions by reforesting my modest little backyard.

Hence my NIMBYism.

The numbers tell the full story. Annual U.S. per capita emissions of CO₂ equal 20.15 metric tons, according to 2005 Department of Energy statistics. That comes out to roughly 44,425 pounds a person.

Now, if that’s the problem, let's look at the solution trees can offer. What they can do to help sop up my CO₂ emissions? The Department of Energy has a simple spreadsheet available online that allows users to figure that out.

I picked two common trees to see what they could do to offset my emissions. One species was the slow-growing white oak and the other the rapid-growing loblolly pine.

Now suppose I planted one of each in my backyard, which is about all that would fit, and left them to grow for 15 years.

By 2023, the oak would have absorbed just 138 pounds, or roughly 63 kilograms, of CO₂. That's just a tad more than I exhale in two months of breathing.

The faster-growing loblolly would do a lot better, absorbing 314 pounds, or 142 kilograms of CO₂, in 15 years. Still, that's about as much carbon dioxide I release to the atmosphere by burning through a tank of gasoline in my station wagon — something that can take just a couple of weeks.

So, should I conclude that any stab I might make at slowing, stopping or even reversing the growth in atmospheric CO₂ levels is useless? No, not if I use less.

Rather than a plant a tree every time I fill 'er up, maybe I could not burn that gasoline in the first place. Maybe I could walk, bike or ride the bus a little more than I do already.

Where can I cut global warming? Not in my backyard — just a few feet over, in my driveway.

Andrew Bridges is a science journalist and author who has written several books for Sally Ride Science, including Earth’s Precious Resources: Clean Air.